Under Floor Hydronic Heating: Money Saver and Comfort?

[velvetfoot]

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.

 

[BoilerMan]

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

 

[Dextron]

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.

 

[JP11]

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

 

[Downeast Farmer]

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....

 

[Downeast Farmer]

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....

 

[Downeast Farmer]

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

 

[nate379]

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)

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

 

[Dextron]

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.

 

[nate379]

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.

 

[Dextron]

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.

 

[StihlHead]

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.

 

[Downeast Farmer]

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.

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?

 

[BoilerMan]

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.

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

 

[StihlHead]

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.

 

[nate379]

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.

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

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.

 

[BoilerMan]

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

 

[Downeast Farmer]

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

 

[nate379]

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).
(broken link removed to http://www.taco-hvac.com/en/products/i%20Series%3Csup%3E%26reg%3B%3C/sup%3E%20Mixing%20Valves/products.html?current_category=184)

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

 

[heaterman]

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.....

 

[StihlHead]

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).

 

[rkusek]

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.

 

[flyingcow]

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

 

[Fred61]

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.

 

[Floydian]

More on the whole MRT thing: (broken link removed to http://www.healthyheating.com/Definitions/Mean%20Radiant.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