# Under Floor Hydronic Heating:  Money Saver and Comfort?



## velvetfoot (Feb 8, 2013)

...or is it mostly comfort?

I guess I could retrofit it in my 2 story house; I'd like to put in hardwood floors upstairs and I bet there's some product or system to do that, and the downstairs has basement access.

I bet it would be really comfortable to walk around, and I realize lower circulating temperature water could be used.  But, what is the economic impact?  Can a setback thermostat be used, even if only for the upstairs, which isn't used too much during the day?  My wife isn't working anymore, so it's not a question of turning it down while we're both at work.  How much of a lead time to get things back up to temp?

Just wondering if it would be for me.  I know my wife would like the warm floors.

Thanks.


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## 91LMS (Feb 8, 2013)

i used ultra fins, snake hangers and 3/4" pex on my application.  absolutely love it.  however i did double up and used two runs per bay (16 oc joist) in my family room where its a cathedral ceiling and lots of glass.  there is a noticeable differance trying to push the heat through just subfloor or hardwood on top of the subfloor.  i feel its more efficient where you mix water temp down and actually loop return water back into the floor.  seems to heat much easier that the baseboard portion on my house. how it's insulated in the bays has a big impact on performance as well.


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## peakbagger (Feb 8, 2013)

Let me start by IMHO - My observations on radiant are as follows.

On new construction it is probably a no brainer if the house is occupied 24/7, if its vacant during the day and some weekends, there may be some debate. I havent seen many radiant systems that work well with setback thermostats. So going radiant is commiting to keeping the house at the same temp 24/7.

I know folks do retrofits of radiant to older homes and some even pay contractors to do it, but I expect the hassle and cost is pretty high. As for a second floor retrofit, if you have high ceiling and dont mind cutting the doors and reworking the trim to install a signficiantly thicker floor it can be done but with a standard 8' ceiling it does eat into headroom a bit. If you have access from underneath, its probably a lot easier but few folks have that luxury unless they want to replace the fisrt floor ceiling.

Most radiant goes in new construction or major retrofits so the benefits are hard to split off from the benefits of generally more energy efficient construction or upgrade of existing systems.

Utlimately the efficiency of a system is related to how low the circulating liquid or air can go to maintain the space. Standard baseboard requires higher temps than radiant so radiant wins unless the baseboard type and area is increased significantly to handle lower temps.  If you have storage on a wood boiler, lower required temps equals much larger storage capacity. Some folks with baseboard and storage advocate just going 24/7 temp setting and run the baseboard temps lower, I dont think they can get near radiant supply temps but can definitely run lower temps throgh a baseboard if it doent need to deal with a setback.

Conventional baseboard relies on convection through a radiator and free air flow into the base of the radiator and out the top. If these paths are blocked, the heat output is lower and frequently the heat is forced up against the cold wall. Radiant doesnt really care about where furniture sits.

Some people claim that they can run a lower temp with radiant than baseboard. I am not sure of this one. Its hard to split off the benefits associated with 24/7 temp setting from the typical baseboard concept of set back thermostats. When a setback thermostat raise the room air temp it takes quite awhile for the surfaces and furniture to get up to the setpoint so during this transition, radiant feels warmer as everything is already at the setpoint.

I also have seen many radiant systems where the pumps run 24/7. This is a large phantom load for power. Depends on the design but assume 200 watts continuous is 4.8 KW per day for the entire heating season.

Fast response to changes in temp is a function of temperature and most wood floors usually have temp limits that limit the change in temp/hour. I expect some floating laminates are less fussy.

In some of the low/no energy homes designs, the designers dispense with radiant and just go with split units. If you dont already have AC and want it, I expect the savings and benefits of some split heat pumps would be equal to or better than a radiant retrofit. They are now good down to -10 degree for heating.

I expect other folks have their opinions so it will be interesting to follow this thread.


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## Downeast Farmer (Feb 8, 2013)

"I also have seen many radiant systems where the pumps run 24/7. This is a large phantom load for power. Depends on the design but assume 200 watts continuous is 4.8 KW per day for the entire heating season."

I would  have thought the pumps ran continuously in all radiant systems, though I'm just now learning about this.  If you were contemplating a retrofit from scratch of a heating system for a large old home (which will never be as  tight as new construction) in Maine, and supposing your design intention didn't allow for fossil fuel use, what would your system include?: gassifier, storage, and radiant heat?


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## Paver56 (Feb 8, 2013)

I put radiant in when I  built my house.  I love it.  It is definately comfortable.  I notice it when I go up my steps-when I walk up that steps I can feel a temp drop since I am getting away from the heat.  My pumps do not run 24/7.  I have a lot of tile and hardwood- be sure that your wood can handle the temp swings.  I used an engineered wood made for radiant heat.  I ran down and back between every joist.  I used alluminum plates in our bathroom, laundry and kitchen.  I wish I would have done the whole house with them. 
If I was to do it over again, I would seriously consider using jip-crete or another lightweight concrete.


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## Nofossil (Feb 8, 2013)

Aside from comfort, one advantage of radiant is that it allows you to get effective heat out of storage at much lower storage temperatures. This can dramatically increase your effective storage capacity. For example, assume 1000 gallons at 170 degrees to start:

Baseboards, lowest usable water temp = 140 degrees. Usable range: 170 to 140, or 30 degrees. At 8345 pounds of water, that's 250,000 usable BTU.
If your radiant allows you to use water down to 100 degrees (not untypical, though different designs give different results) that's 70 degrees range or 584,000 BTU from the same storage tank.

There's also no law against having baseboards AND radiant....


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## VT_Bubba (Feb 8, 2013)

This is a very interesting thread for me.  I had personally romanced about the comfort advantages of Radiant Floors and was very interested in the potential efficiency advantages. 

 As part of my Solar DHW research and installation, I had hoped to super size my solar design to help heat my house, and had seriously considered adding some low temp radiant to my 1st Floor where I had access for the radiant installation from the basement  After some very long, deep, soul searching, and some calculations I concluded :

1) Solar Heating did not make sense for an existing Low Mass, High Temp, Base Board house.
2) Here in VT, during Dec\Jan\Feb we have VERY Large BTU needs, with very little available Sun (BTU's).
3) Because it's only me and my wife, using set-back T-stat's is a major part of our life style, which offers real potential energy savings for us.
4) I could not convince myself of any large efficiency gains (energy savings) inherent to Radiant Heating, and certainly nothing to match the potential energy savings that I get from my set-back T-Stats with BB High-Temp Heating.  If we heated the whole house 24hrs a day then any potential Radiant Efficiency advantages might make more sense. For our life style and existing BB heating system (pellet boiler, with Oil Back-up), I concluded that Radiant Heat and heating 24hrs a day, would actually use more energy than using my set-back T-Stats.
5) I concluded that Set-Back T-Stats do NOT work well with Radiant Heat.
6) Radiant Heat makes a ton of sense if you have a High-Mass System Design (Solar, Geo, Boiler with Storage, etc...).  But my entire heating system design (Both pellet boiler and Oil Boiler) is based on very low mass, high temp, which works well with set-back T-Stats.  
7) I concluded Radiant Floor is primarily for comfort and did not have any large inherent efficiency gains, unless you had some type of High Mass, low temp, heating system to go with it.

Just My Humble Opinion here, based on my personal situation and research.  I'm hoping some Heating Professionals will join the conversation and discuss the "Inherent Efficiency Gains\Losses of Radiant Heat" in general.  Very Interesting Topic !  

VT_Bubba


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## BoilerMan (Feb 8, 2013)

As I sit in a chair on a radiant slab covered with porcelain tile. The storage point that NoFo made can be done with H.O. (read low temp) baseboard, oversized CI radiators, or panel radiators like they use in Europe.
Radiant comfort is excellant, but to make a true scientific energy audit we'd ahve to heat the same building with both types of radiation systems and see lower uses. Any low temp system will win with the same type of heating appliance, as the lower operating temps will increase efficiency slightly, staying above condensation point in non-condensing equiptment. This said, if you were going to use gas (Nat or LP) a modcon boiler connected directly to a low temp system (any of the above mentioned heat emitters) will condense all the time and get the most heat out of the gas. With a wood fired system, and storage, same as NoFo said less physical volume can store more useable BTUs. Radiant-retro is a big job and depending on the type and scope of the renovation, I'd opt for a low temp emitter first. Anyone who _*builds new*_ would be foolish IMHO to not use some type of low temp system. Conventional fin-tube heat emitters in new construction mean (to me) they cheaped out or didn't do their reasearch on modern hydronics.

As for the circulation issue.... In Europe they use almost exclusivly constant circulation with full outdoor reset. This lowers water temps as the outdoor temp goes up and in theory the heatloss of the building also lowers. This does not take wind into account or solar gain. I set up most systems with a partial-reset meaning a heatloss calculation, and slightly higher temps for margin and installing a conventional wall thermostat. Full reset has no thermostat and indoor temp is a direct function of water temp. 200watts is a good number unless smart circulators are used. If VS circs are used the total wattage from all associated (constant circulation part) would more likely be in the <100 watt range. I do not like a circulator running 24/7 no matter how low the wattage, but that is just me.

My $0.02

TS


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## dogwood (Feb 8, 2013)

Velvetfoot or anyone, considering the amount of construction work needed to put in underfloor radiant, might panel radiators be a better way to go for you? I would think you'd have almost all the advantages of underfloor with lower operating temps and increased storage capacity, plus the advantage of easier installation, less construction and construction related costs, and less of the inevitable household disruption, not having to leave the system on 24/7, and easy regulation of temps room by room with trv's.  

Before I decided to not put in-floor radiant in my own home during construction, one of the deciding factors was not wanting to have a 3/4 inch sub-floor and 3/4 inch oak flooring between the heat emitter and the space being heated upstairs. Downstairs was less of a concern since it is a slab, originally intended for radiant, before I decided against going that way. I never did figure how I could install a hardwood floor over the slab with radiant without creating a messed up situation.

I'm no expert on this, so I'd be interested in any thoughts on underfloor radiant vs. panel radiators for your situation.  

Mike


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## bmblank (Feb 8, 2013)

Radiant floor can be done two ways, and the conversation is bouncing back and forth with much confusion. One way is to staple it to the bottom of the sub floor between the floor joists. Very easy to do. Watch it if you still have nails/screws to put in. I stapled my pex to some spacers so the floor staples had no chance of hitting it. Another way I'd to put it on top of the sub floor. Many ways to do that. I've seen it stapled down and concrete poured over it. Very good way of doing it, but hard to retrofit. You sort of need to plan for that beforehand. That way would also be way better for the passive solar thing. I've also seen a track system that has aluminum track for the pex to fit into spaced apart with some sort of plywood. Basically the flooring is applied directly on top of that, but stapled into the plywood spacers.


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## maple1 (Feb 8, 2013)

Pex in the floor joists also doesn't have to be up tight to the subfloor. It can be 'suspended' a little bit, then insulated.


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## JP11 (Feb 8, 2013)

wirsbo has an expensive.. but great stapler.  It won't fire unless the two "ears" on each side are touching subfloor.. AND... pipe is in the built in U.  No chance of stapling the pipe.

my plumber let me use his stapler.. and I did the whole house myself.  Staples are about 1,5 deep.. and about 2 wide, so pipe can move laterally, but held tight to the floor.

Using this.. I used no aluminum transfer plates.  I left an inch of air space.. then used 1.5 inch foil faced hard foam between trusses.  Each truss bay is about 2', and has 3 pipes in it.  Leaving the floor above with a pipe every 8"

JP


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## bmblank (Feb 8, 2013)

maple1 said:


> Pex in the floor joists also doesn't have to be up tight to the subfloor. It can be 'suspended' a little bit, then insulated.


Indeed. Bottom line is, the closer to your feet you can get it the better, but there are tradeoffs to get there.


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## Downeast Farmer (Feb 8, 2013)

There's research out of Kansas State University that shows that those expensive heat transfer plates make a big difference, but they sure do add to the cost and complexity of installation (if retrofitting to the underside of an old floor with cut nails poking through from the hardwood floor installation above).  Are you satisfied with your installation without plates, JP?  Is yours a really tight home?  What size pex are you using?


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## Downeast Farmer (Feb 8, 2013)

And I imagine without heat transfer plates, you'd have to run your radiant floor at a high temperature.  What temperature does anyone here run their radiant floor pex?  With or without heat transfer plates?


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## BoilerMan (Feb 8, 2013)

A staple up or suspended system is referred to as a dry system.  A wet system is when the tubing is buried in a concrete or gypsum slab.  This slab can be a thin (gypsum or gypcrete) pouring over a wooden subfloor, this weight needs to be accounted for as bmblanc pointed out.  A wet system has the lowest operating temps per but given due to the surface area of the pex being in full contact.  Thin slabs, pour-overs, or gypcrete slabs are all the same thing for the scope of our conversation here.  Thin slabs are much more conducive to setback thermostats due to lower mass. 

Aluminum transfer plates under a subfloor reduce the temps needed but are expensive.  A staple up or suspended system is considered a medium temp heating system, but as JP said is very easy and fast (read lower job bid) to install.  It still has the radiant benifits but needs higer temp water due to the lack of surface area contact with the pex.  This can be accounted for with more pex runs like JP did with 8" O.C. 

Radiant floors on top of the subfloor can be done with sleepers and running the pex in the voids between sleepers with plywood on top covered with the flooring.  This is like the staple-up system but is on top of the subfloor, good for retrofits floors with a finished ceiling below the joists. There are also special cut boards that are precut for this purpose but I can't remember who makes them, Wirsbo/Uponor?  They are wicked expensive....   

Bottom line in no order:
Dry radiant
1. Staple-up
2. Suspended
3. Over subfloor installs
4. Aluminum transfer plates (also can be used as radiant wall)

Wet Radiant:
1. Tubing in concrete slab on grade
2. Tubing in gypcrete over wooden or metal subfloor (known as: pour-over, thin-slab, or light-weight-slab)

This list may not be complete as it is off the cuff.

TS


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## 91LMS (Feb 8, 2013)

i was nervous of the fact that i had to construct my hearth and nail down my flooring so opted to go for the ultra fin setup.  it does a great job imo.  also was advised that with thick hardwood flooring i might be better off with ultra fins so that i dont overtemp my floor.  do the staple up plates get much noise as the pex expands and contracts?  has anyone run into issues using staple up and having too high of floor temps in really cold temps?


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## Downeast Farmer (Feb 8, 2013)

So, Taylor, what temp is medium temp for the suspended pex?  If you can run your pex+heat transfer plates down to 110* or so, to what temp can you run the suspended pex?  Over the long run, for your own system that you weren't bidding out, would you be better off going with the heat transfer plates (after having cut or ground off all those protruding nails?).


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## BoilerMan (Feb 8, 2013)

Floor temp is directly related to the heatloss of the structure.  This is the same with all radiant types, however there may be a more noticeable hot spots in staple-up, suspended or over the subfloor systems.  The floor has to be warm enough to match the heat escaping from the building.  This is why in super insulated houses radiant floors are not noticed much, they don't need to be much over room temp to keep the place warm.

TS


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## BoilerMan (Feb 8, 2013)

Downeast Farmer said:


> So, Taylor, what temp is medium temp for the suspended pex? If you can run your pex+heat transfer plates down to 110* or so, to what temp can you run the suspended pex? Over the long run, for your own system that you weren't bidding out, would you be better off going with the heat transfer plates (after having cut or ground off all those protruding nails?).


All depends on the building's heatloss.

If money were no object I'd go with plates or a pour-over. 

Personally I hate basements, in my line of work, I've been in way too many which were musty, flooded at random times, or had expensive radon issues, these were in new and old houses.  I'd want to finish part of mine if I built one and these are all not gonna fly in a living space.  This coupled with the benifits of a radinat slab-on-grade's huge mass I built my house on a slab. 

TS


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## JP11 (Feb 8, 2013)

I did the staple up myself.  My builder and the plumber both told me not to bother going with the plates, as there was a lot of cost and labor (mine) involved.

My house had a sizeable budget, so it wasn't make or break.

The idea, as I was told, was for that air space and pipes to be the whole heat source.  My pipes on the staple up run about 140 to 145 degrees.

There's 3 zones upstairs (which is the main floor of the home)  1200 sf photo studio for my wife.  Kitchen, Laundry/half bath, living/dining, Mudroom, all another zone probably 1400sf.  Then the bedroom, master bath, walk in closet on the last.  about 1000sf there.

Works well.  I can't complain a bit.  Toughest part of running all the loops was the figuring.. figuring where to pull the end thru and from in order to not jump the trusses more than once.  I got good at it... of course about the time I was done.


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## nate379 (Feb 8, 2013)

I'm not a big fan becaues of the SLOW reaction times.


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## Downeast Farmer (Feb 8, 2013)

By which you mean, nate379, that you have to run at desired temp all the time because it takes to long to heat up?


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## BoilerMan (Feb 8, 2013)

nate379 said:


> I'm not a big fan becaues of the SLOW reaction times.


 
Please read post #16 that depends on the type of radiant system.

Also I've seen buildings spec'd for both a radinat floor and a supplemental fin-tube (baseboard) system for fast-response.  Y'all talk like the high mass is a bad thing, it allows me to fire once a day and not have "storage" as most think of storage. 

TS


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## Downeast Farmer (Feb 8, 2013)

Well, I'm not part of "y'all"; I'm sold on high mass or storage--just trying to figure out what nate is referring to.  I'm also sold on no set-back thermostats on radiant installations because they work best that way, according to VT_Bubba....Not the case?


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## velvetfoot (Feb 8, 2013)

Would running a mix, say underfloor hydronic, on the first floor, and conventional convectors on the second, be a problem?  I can see a bump in convector capacity would help.


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## BoilerMan (Feb 8, 2013)

Velvetfoot:  No problem useing fintube and radiant in the same system, just keep in mind that the high temp emitters negate the low temp benifits of appliance efficiency gains or storage-stretching.  Size the convectors to the temp used in the radiant.  Panel or CI rads may be a better option to keep system temps all low.

Set-backs can work on lower mass pour-over slabs, or any of the dry systems if high temp water is used for the rapid rise time, floor overheating then becomes an issue, especially if it's a large volume room like high ceilings. Still no where near the response time of panel rads or fin-tube. Panel or cast iron radiators generously oversized for low temp water can be the best of both worlds. If I'm gone for a few days and there has been no heat in the house, upon return and the house is in the 50's I build a fire in the wood stove for quick response and a fire in the boiler for long lasting heat.


TS


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## Dextron (Feb 8, 2013)

I used 1/2" PEX on 8" centers fastened under 1 1/8" subfloor with aluminum heat transfer plates.  I used I-Joists so I fastened foil faced Polyiso to the bottom of the flanges leaving a 1 1/2" gap between it and the subfloor.  Zoned every room separately and ran thermostat wire from each room to the manifold.  Quickly found out that reaction times are so slow that I just leave all the zones open and the pump on all the time and adjust water temp as needed.  The controller for the mixing valve has an outdoor reset function but I haven't managed to set it up to where I like what it picks for temps so I just manually set it as needed.  It really doesn't take much adjustment - I probably run most of the winter at 90 +/- 2 (degrees F).  Last winter we had six weeks of about as nasty cold as I've seen and never went over 95.  That has been a little disappointing to my wife as the floor never feels warm. This is fed by an oil fired water heater as I am still in the research/planning stage for a wood boiler. Really wish I had looked into them when I built this place - it would be a lot easier than adding one in now.  I must say I have learned a lot on hydronics browsing this forum the last few months.  I feel kind of dumb that I never looked up a lot of this stuff before as it is basic physics. I guess I got lucky with my seat-of-pants estimates as my system works pretty well.


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## JP11 (Feb 8, 2013)

Downeast..

Not that I would spend the money on one right now.... but the new fancy Nest Gen 2 thermostats supposedly "learn" how long it takes to move radiant, and will adjust accordingly.

I can see a benefit to a internet enabled thermostat.  On sunny days, my living room will overshoot a bit.  If it "knew" it was going to be sunny... it could let the temp be just a couple low letting the sun do its thing.

JP


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## Downeast Farmer (Feb 8, 2013)

Where do you live, Dextron, with that 90* radiant water keeping you warm?  I don't think there are enough BTU's anywhere on the coast of Maine to keep my place warm....


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## Downeast Farmer (Feb 8, 2013)

Those low temp CI radiators seem like a perfect answer, Taylor, if I could figure out where to put them.  I grew up with them (though high-temp then) and have missed them ever since.  Those new European valves that act as thermostats would be perfect here where the kids come and go and we can never predict how much of the house we'll need to heat from one day to the next.  I'd need to have a lot of radiator sections to run at low temperature....


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## Downeast Farmer (Feb 8, 2013)

Thanks, JP; my learning curve is getting steeper....


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## nate379 (Feb 9, 2013)

A staple up system isn't quite as bad, though it also doesn't have as good of a heat transfer either. My setup is in a 4" slab for the house and 6" for the garage.

Yeah. Takes several hours to warm up a few degrees. With using the stove it goes cold more or less so it takes 10-12hrs for the slab to get enough heat in it before it will really start doing anything.

One year, 2010 maybe, I was gone for 2 weeks in the winter and I had turned the heat to 45*. I got home late after a LONG flight, no mood to mess with the stove. Kicked on the T Stats to 68* and when to bed. Got up about 10hrs later and it was barely over 55*. I let it go just to see and it took close to 24hrs to get up to 68*, roughly 1* an hr.

The other thing I don't like is there is no between room air exchange. If I were to design my heating system I would include forced air, maybe not even do the floor heat.

I will agree that the "storage" can be nice, house will hold indoor temp at well below 0* temps outside for close to 24hrs without having power (has happened before) The downside is that it can also overheat the house if it's cold at night and warm in the day. I sorta fixed that by installing an outdoor reset.

Even when just on the floor heat, the floor isn't hot or anything.  Can't really tell it's on actually.  The floor is roughly room temp (and it should be) 



Downeast Farmer said:


> By which you mean, nate379, that you have to run at desired temp all the time because it takes to long to heat up?


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## Dextron (Feb 9, 2013)

Downeast Farmer said:


> Where do you live, Dextron, with that 90* radiant water keeping you warm? I don't think there are enough BTU's anywhere on the coast of Maine to keep my place warm....


 
I'm out on the west coast of Alaska.  As is often recommended throughout this forum I used quite a bit of insulation when I built this place.  Though I am in complete agreement with the theory of spending money on insulation before fuel I do have one thing to add - I think making the structure as airtight as possible is even more important - at least in high wind areas.

Current conditions: outside temp -8F, wind 12 to 16 with gusts to 24, inside temp 70, floor heat temp 91.


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## nate379 (Feb 9, 2013)

Why are you loosing 20* from your floor temp to your air temp?

If I set my T Stat to 68*, the floor might get to 75* in the warmest spots.  My water temps at the boiler are about 130* and usually the return temp is 100-110*, depending on slab temp.


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## Dextron (Feb 9, 2013)

nate379 said:


> Why are you loosing 20* from your floor temp to your air temp?
> 
> If I set my T Stat to 68*, the floor might get to 75* in the warmest spots. My water temps at the boiler are about 130* and usually the return temp is 100-110*, depending on slab temp.


 
I should have defined my numbers a little better.  91 is at the supply manifold.  I would have to take my IR gun to the floor again to see but your 75 sounds close for floor surface temp.


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## StihlHead (Feb 9, 2013)

My experience as far as _comfort_ is that hydronic radiant heat it is by far the best heating that you can have. Way better than burnt air furnaces, wood stoves, or wall heaters. The heat is even and does not dry out your skin or the air in the house. You also do not get the rise and fall in heat/cool that a typical forced air furnace has. It is also better if you have allergies, like I do. Depending on how the pex is routed and zones are set up, there can be cool spots if they are not tuned right, or there are kinks in the pex lines. They are not the cheapest systems to install though, and running them may or may not be economical based on the source of energy used to heat the loops. Supposedly they are 30% more efficient than forced air heating. They can be retrofitted and run off of several heat sources, such as electric or wood boilers, solar or heat pumps, or a combination of them.

The temp of the floor loop is dependent on the type and thickness of the flooring. Usually from 100 deg. F. to about 140 deg. F.? That is the temp range on the Honywell mixing value that I installed. As for floor loops running all the time, that is not the case in most systems that I have seen, and was not the case in the one I lived with and redesigned to run off of an OWB. That system was on demand and originally run off an electric boiler that came on when the standard wall type thermostat called for heat in the house. I retrofitted that system to run off of a flat plate Hx from an OWB that fed a mixing valve to feed the floor loops in the house at 110 deg. F. The floors in the house were tile and hardwood floors on a raised pier foundation. The OWB water loop ran constantly, between 160 and 185 deg. F. If we left on a trip in winter I closed off the OWB loop and turned on the electric boiler and dropped the t-stat to 50 deg. F.

The downside as mentioned above is that you need a pump to run the system, and if the power goes out your heating goes out with it. Either a generator is needed, or as we did, we used a wood burning insert in the living room and slept in there at night for a few days until the power came back on. Set back t-stats are not as effective, as the hydronic loop heats up and cools down rather slowly. However, I usually set the-stat to 68 at midnight to noon, and 72 from noon to midnight. That gave us a noticeable wood saving over time in the OWB.


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## Downeast Farmer (Feb 9, 2013)

StihlHead said:


> As for floor loops running all the time, that is not the case in most systems that I have seen, and was not the case in the one I lived with and redesigned to run off of an OWB. That system was on demand and originally run off an electric boiler that came on when the standard wall type thermostat called for heat in the house.


 



StihlHead said:


> The OWB water loop ran constantly, between 160 and 185 deg. F. If we left on a trip in winter I closed off the OWB loop and turned on the electric boiler and dropped the t-stat to 50 deg. F.


 
Stihlhead--don't these two statements contradict each other?  This is what I don't understand about these systems: do you have to run pumps constantly or as needed?


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## BoilerMan (Feb 9, 2013)

nate379 said:


> My setup is in a 4" slab for the house and 6" for the garage.
> 
> Yeah. Takes several hours to warm up a few degrees. With using the stove it goes cold more or less so it takes 10-12hrs for the slab to get enough heat in it before it will really start doing anything.
> 
> ...


 
Your system should respond MUCH faster than that.  Two stage thermostats would solve this problem.  When the second stage contacts close (you turn up the heat more than a few degrees) and the outdoor reset is bypassed and the supply to the slab goes into MAX setting ie. 130 or something depending on flooring.  This would make the system burn more fuel but only to keep you happy.  Outdoor reset is keeping the slab only a few degrees warmer than calculated to keep you at 70 or whatever the calcualtion was based on.  This is for fuel savings and con
 stant circualtion or near constant circulation.  This is how I would solve your problem with minimal hardware.  The hardest thing may be pulling thermostat wire with the extra conductor if you only have standard 18-2 wire now.  I generally pull some CAT-5 or 22-4 for this very reason.  Someday someone will want to do something that needs more conductors than the standard two. 

As for scorched air furnaces, well no comment, mobile homes come with them for a reason.   

TS


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## StihlHead (Feb 9, 2013)

Downeast Farmer said:


> Stihlhead--don't these two statements contradict each other? This is what I don't understand about these systems: do you have to run pumps constantly or as needed?


 
It depends on how the hydronic floor loop is designed. In the case of a simple electric boiler hydronic system, the floor loop is run on demand. A t-stat is set to come on and go off between a set temperature range. When the t-stat comes on, the electric boiler and pump come on and water is heated and circulated through the pex lines. When the t-stat goes off, the boiler and pump go off.

Now add some complexity to the above. I added an OWB hydronic system to run a Hx (heat exchanger) to replace the electric boiler. It was a separate hydronic loop that was driven by a separate Taco pump. That loop ran 24/7 and a separate t-stat on the boiler kept the temp in the boiler loop between 160 and 185. So when the t-stat in the house came on, it only turned on the floor loop pump and the heat was extracted from the Hx fed by the OWB loop and distributed through the house.  

So one OWB loop constantly runs to feed heat to a separate on-demand floor loop in the house that runs on demand. Two separate system loops. These can be set up to run off of solar heated water tanks, indoor or outdoor wood or coal fired boilers, or other sources of heat. There are other types of hydronic heating design loops though, and some run constantly and use mixing or tempering valves to adjust the floor loop temperature. I have only designed isolated loop systems that run off of a Hx myself.


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## nate379 (Feb 9, 2013)

I'm by no means a pro HVAC contractor, I just know how my system works and I thought it might be helpful to give my 0.02 to the others asking about it. I do realize its an in slab system so staple up will be different.

The outdoor reset runs the boiler at anywhere from 135-200* depending on the outside temps. The floor loops have a mixer connecting the primary and secondary loops of the boiler and I have it set to around 130*.

I didn't design the heating system, though it seems to be put together properly from everything I have read. When I bought the house having the floor heat was a big consideration in the purchase. Everyone said it would be so nice, barely uses nat. gas...can heat the house with a candle for a boiler, etc. 

Now having lived in the house for 4+ years I would not setup a house with just floor heat.



Taylor Sutherland said:


> Your system should respond MUCH faster than that. Two stage thermostats would solve this problem. When the second stage contacts close (you turn up the heat more than a few degrees) and the outdoor reset is bypassed and the supply to the slab goes into MAX setting ie. 130 or something depending on flooring. This would make the system burn more fuel but only to keep you happy. Outdoor reset is keeping the slab only a few degrees warmer than calculated to keep you at 70 or whatever the calcualtion was based on. This is for fuel savings and con
> stant circualtion or near constant circulation. This is how I would solve your problem with minimal hardware. The hardest thing may be pulling thermostat wire with the extra conductor if you only have standard 18-2 wire now. I generally pull some CAT-5 or 22-4 for this very reason. Someday someone will want to do something that needs more conductors than the standard two.
> 
> As for scorched air furnaces, well no comment, mobile homes come with them for a reason.
> ...


 

As far as the forced air being bad on allergies, I don't so much agree. You have air flow through the whole house, from room to room and that air gets filtered. With floor heat there is NO air circulation or filtration.
Yeah that does mean that nothing is getting blown around, but also means the air quality can get pretty poor.
Maybe "ideal" would be a filtered HRV system that is connected all around the house? I dunno.

I have lived in a few houses with forced air and I really liked the fact that I could come home to a 45* house, kick on the heat and in an hour or two the house was warm. The floor heat doesn't work great for those "a bit chilly" fall or spring nights either.


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## BoilerMan (Feb 9, 2013)

nate379 said:


> I have a mixer connecting the primary and secondary loops of the boiler and I have it set to around 130*.


 
There is your slow response problem. The reset is only controlling the boiler temp saving some fuel. The fixed floor temp is causing the slow response time. If the floor were on a reset control and the two stage thermostat, you's get different floor temps based on outside temp, and thermostat call (primary: reset temp, secondary: high temp).

A fixed temp system is good for small radinat retrofits, but a large slab  under living space (not garages or something) respond very well to a motorized mixing valve or injection control via outdoor reset controller.

TS


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## Downeast Farmer (Feb 9, 2013)

Stihlhead--
Why does the OWB loop have to run continually?  What would be the least-operating-cost way to run the radiant loop?


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## nate379 (Feb 9, 2013)

I know there is an reset type mixing valve offered, my neighbor has one on his heating system (done by the same contractor not even 6 months apart).
http://www.taco-hvac.com/en/product...ing Valves/products.html?current_category=184



Taylor Sutherland said:


> There is your slow response problem. The reset is only controlling the boiler temp saving some fuel. The fixed floor temp is causing the slow response time. If the floor were on a reset control and the two stage thermostat, you's get different floor temps based on outside temp, and thermostat call (primary: reset temp, secondary: high temp).
> 
> A fixed temp system is good for small radinat retrofits, but a large slab under living space (not garages or something) respond very well to a motorized mixing valve or injection control via outdoor reset controller.
> 
> TS


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## heaterman (Feb 10, 2013)

Shotgun radiant thoughts.........In no particular order.

The higher the mass of the system the less viable setback periods become. Rough examples: 4-6" concrete slab response time 8-16 hours. Under floor radiant with plates or without figure from 4-12 hours. Above floor radiant panel such as Climate panel or Warmboard, 1-2 hours  But ohhhh the comfort level of a high mass system.......It's like walking into a nice warm blanket when not only the air temperature is 70 but also everything in the room is that temperature also. (This is what's called mean radiant temperature or MRT.)  It's what makes a forced air system at 70 feel a bit on the chilly side when the weather gets cold and a radiant panel system feel the same all the time. A classic example is walking down the frozen food aisle in the supermarket when you are surrounded by cold glass cases, The air temp will be pretty much the same as the rest of the store but because you are surrounded by cold objects, physics dictate that heat leaves your body faster and you "feel" cooler.
But I digress.......
Back to setbacks, it can be done but you'll wind up with the heating cycles far in advance of what you would normally schedule on a hot air system and even then you will find that the warmup and cool down periods are gradual.
Energy savings from a radiant system result mainly from the ability to run a lower room temperature while still feeling comfortable due to the increase in MRT those systems offer. This is determined by the user and his/her physiology.
Typically the human body is more comfortable if the feet are warm while the upper torso and head are a bit cooler. Hot air system of any kind run the total opposite of that especially in rooms with high ceilings.

Panel rads make a good compromise because some of the heat they give off is in the form of long wave radiant energy like a true radiant system. Baseboard is nothing more than a hot air system that is convective instead of fan forced.  ...leaves me kind of ....meh.....


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## StihlHead (Feb 10, 2013)

Downeast Farmer said:


> Stihlhead--
> Why does the OWB loop have to run continually? What would be the least-operating-cost way to run the radiant loop?


 
There are several reasons for running the OWB loop continuously. You want to mix the water in the OWB tank and water loop to keep them uniform so that the boiler is better controlled by the t-stat in the boiler which controls the OWB damper. Shutting off the loop would cause hot and cold spots in the lines and uneven temps in the boiler and lead to more erratic conditions. Keeping the loop temperature up and uniform also makes the heat in the lines available on demand for all the devices plumbed to draw heat. We had more than just the hydronic floor loop connected via the Hx. We also had a water heater connected to it on a smaller Hx that had a passive loop run off of convection. No pump required for that, the heated water heated in the Hx rises from being less dense, and cycles water through the hot water heater. If you cool off the Hx in the boiler loop the convection flow stops. The only loss for a boiler loop running all the time is the electricity of the Taco pump (which is small), and line losses which were about one half a degree F. per loop run (it varied with outdoor temps).


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## rkusek (Feb 10, 2013)

I'm going to throw in my 2 cents because I don't see anyone mention what I've witnessed over the past few years.  I have decided to abandon my desire for radiant heat which would have been staple up with plates on main floor and radiant walls in basement (hot rod posted a link on this awhile back).  I also liked the euro rads that Heaterman has installed and would consider CI rads if it wasn't for my wife.  I no longer think any of this is worth the cost to install (upwards of 3-5 grand with pex, insulation, plates, rads, pumps, controls, labor).  My plain old air source HP (need the AC in Nebraska) is not the scorched air I have lived with in the past or that most of what you guys are familiar with I'm guessing.  Our 2009 stick built ranch is well insulated but not super insulated (2x6 R-19 walls, R50 ceiling -R19 batts with blow in on top) and we have decent Pella windows.  The HP throws out the usual "lukewarm" heat and still works down to 0F abeit with some shots of resistance heat during the defrost cycles.  It does run considerably more than a gas forced air but you don't have the hot-cold-hot-cold feel and the air doesn't get dried out.  I do have the built in humdifier which may help some.  I will say that in a poorly insulated or older drafty home this may not work.  I added the water to air HX myself fed by my EKO 40 and this also delivers surprisingly good results.  Since the HP keeps the tstat exactly at the setpoint (ie. turns on at 69 if the setpoint is 70 and then shuts off before it hits 71) I simply added a 2nd tsat for the wood side set a couple degrees higher than the HP one.  The wood tsat is a simple single stage made for resistance heat so it also maintains the setpoint to the degree and I use it to run the blower and circulate water through the HX.  I usually run the wood at 69 and the HP at 67 or so.  When my boiler runs out of wood and the underground loop between the barn and home cools below 89 degrees, the aquastat will stop the blower & circ and the home will need to cool a couple more degrees before the HP kicks in.  Even when it is 0 F outside, the water fed HX can maintain the setpoint until the water hits the 89 degree cutout.  When the boiler and loop is hot 170+ (no storage hooked up yet) the air handler will cycle much less and it probably functions more like a typical forced air gas furnace.  When my 1000 gal storage is actually operational, I'm thinking of only adding heat to the primary loop from storage to maintain it at no more than 120 or 130 degrees when the boiler is out.  I see no reason to send 150-180 degree water underground to the house.  In fact, even though the EKO connects to the primary loop now I wonder if it would be more efficient to sever this connection and go straight to the storage tanks making it easier to get them up to maximum temperature.  Having the house always at the exact setpoint makes it very comfortable for us.  None of us seem to get colds anymore either compared to our previous 2003 FA gas furnace 2 story home that always had uneven heat.  One thing I wish i had was the more sophisticated air handler fan that varies it's output.  Some of them run on as little 95W on the lowest setting.  http://www.greenbuildingadvisor.com/community/forum/mechanicals/20709/swapping-ecm-psc-fan-motor
I'm actually looking at buying one of these ECM retrofits above.  One of them can run on 120V making an backup battery/inverter setup a doable option during a power outage.  If we didn't have the huge AC demand in the summers spending money on radiant would make more sense but I can't justify it now.  Incidently, January electric bill was $188 on our 4400 sq ft home.   I only had about 2 cords of good dry wood this year so I have only been burning during the colder days & nights (<25 F) to keep my barn in the 40's.


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## flyingcow (Feb 10, 2013)

Downeast Farmer said:


> And I imagine without heat transfer plates, you'd have to run your radiant floor at a high temperature. What temperature does anyone here run their radiant floor pex? With or without heat transfer plates?


 

I have staple up wirsbo w aluminum plates. 120/130ish water temps


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## Fred61 (Feb 10, 2013)

heaterman said:


> But I digress.......​


 I think it,s called "putting things into perspective". People go through life with all these things happening around them and don't even question them.
.
I have staple up radiant from Radiant Floor Co. of Barton Vermont and used the annealed plates throughout. The whole house is a rework and the floors ended up being 2.25 inches thick so the combination of plates and 140 degree water work fine. I can still heat with water temperatures down to 100 but thats because of the low demand of a well insulated house. It has mixed benefits. The thick floor acts as storage so there's a greater amount of time between cycles but the room temperature will overshoot a little because of the latent heat.

My floors are either tile or hardwood.


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## Floydian (Feb 10, 2013)

More on the whole MRT thing: http://www.healthyheating.com/Definitions/Mean Radiant.htm#.URe7UaU0V8E

Great piece from Mr. Bean and mandatory reading, IMO.

Just another great reason to build better enclosures and yet, somehow, standard construction still rules the day. Shame.

Noah


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## heaterman (Feb 10, 2013)

A quote from "the Bean".

"I say, if building codes dropped the reference to controlling air temperatures and switched the requirements to controlling mean radiant temperature, building performance specifications would have to change overnight.
Bad buildings have low MRT’s in winter and high MRT’s in summer; this contributes to large differences in the vertical air temperature; creates excessive drafts and increased radiant asymmetry. Bad buildings also have uncomfortable floor temperatures and are challenged to maintain reasonable levels of humidity." Bean, R., The Big Picture, Beyond the Benchmarks: Better Buildings, August 2011

He is dead on. If you can hit a MRT of 65-68* you will be fully as comfortable there, probably more so, as in a house with a MRT in the 50's and an air temp of 72+.


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## ihookem (Feb 13, 2013)

Hey Stihlhead, Aren't you Windthrown on another sight????? Gotta be you. Anyway I have hydronic in my living room and Hx in the rest of the house. I have some questions about this cause most is over my head. Does hydronic use less energy by 30%? Also, How can I find out how to design a hydronic system? Is there anywhere on the net I can design a system for my house. I ask cause my plumbers fried said he would do it but he charges 90 bucks an hour. Not exactly bad for a guy who know what he is doing but he is 1 hour each way. How do you all figure out the pump sizes, mixing valves, ect.??


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