Garn 1500 Arrived - Can't afford to hook it up

[Jim K in PA]

I did not see a model/part # on those labels, but based on the data tags, age of the install (3+ years) and your sketch, I would guess it is not a mod-con, but that should be confirmed. Can you give us a Burnam p/n to look it up?

Also, let's not rush to judgement just yet on the original installer. What is the operating range for the furnace now? He may have set it low and varied the output of each zone by coil density alone, rather than by coil density and temp.

Also, even if the water were hotter than desired, you should not be burning that much more propane, as the stats will just cycle the pump and zone valves on/off more frequently. Do you have issues with the room temps running above the T-stat setting?

If he has the Burnham running at low temps (130-150?), you can add a single mixing valve to your existing manifolds to keep things as they were, or use a mixing valve on the GARN side of the house loop. Lots of options. First, let's get your Burnham propane unit figured out.

As to your updated sketch, you got it about 99% to what I was describing. You do not want or need to have a dedicated cold water feed to the primary loop. The GARN is an unpressurized system. Some folks (like me) plumb a feed line up to the manway collar due to access issues, but you can just drop a hose into the manway for filling. Water loss is minimal and can be checked during your biannual (biennial?) water testing. I am adding a vented boiler sight glass to my tank to have a visual on the water level, but that is just me.

 

[rvtgr8]

The boiler is a three year old Burnham - Series 2 (Model B) Gas - Fired Boiler. I have been unable to find any part numbers or serial numbers. It appears that the temperature is set at 168*, which to my uneducated eye seems a little high.

 

[slowzuki]

I don't know if you're thinking the same as me Jim but if its a mod-con it could easily and efficiently handle the low return temps the current install would give. Looking at the numbers though the efficiency seems low for a condensing unit. Robert does you boiler have metal vent or PVC? Model number is the best way to tell of course.

Jim I also agree they may have used high water temps by design. It can work in thick slabs with wide tube spacing. Not so good in thin insulated slabs due to striping and excessive localized temps.

Another option is to use a variable speed pump on the HX instead of mixing. I just don't like using tons of pumps as you start using a lot of electrical power which can be avoided by careful design.

How many direct tappings are there on the Garn? The loop can be avoided when you have direct access to the storage and loads that need high temp like those he has shown. Circs with integral flow checks on a large closely connected manifold could also be used to eliminate the loop with no ill effect and it would kill off the two pumps that will use the most power.

EDIT Just saw your post Robert, definitely not a condensing model. The low return temp is likely not been a problem due to the cast iron high mass style construction but it could lead to problems.

 

[rvtgr8]

I also would like to say that I am not upset with my plumber. There is not a nicer guy on the planet. I am just pointing out that he is no longer available so that I might ask questions of him. I am upset that I did not do my homework up front. I am the one responsible for any of this. I had an engineer offer to do the layout initially, but as is the case with tight budgets, I took the less expensive path. My bad. He would have installed it anyway I asked. :red:

 

[slowzuki]

I'm guessing the high price you were quoted may have involved work to change the existing installation too which Jim is getting at. If it was designed for the high temp water, it will make the connection of the Garn dead simple, but you will likely want to add features to protect the propane boiler from the low return temps or you will want to replace that boiler with one which has a stainless hx once the cast iron one dies. It may last a long time depending on how the controls on your system are setup.

Even as the garns water temp fall, the Garns thermal mass may be able to keep the return water preheated even if the gas boiler has to come on to make up load. This may protect it and extend the life.

 

[rvtgr8]

I am pretty certain that the Burnham is not a condensing unit. The vent, dampener (automatic), and flue are all metal. Thank you again for your interest.

 

[rvtgr8]

I also type with the speed and deftness of a glacier so I am not able to keep up with you very well.

The radiant is placed in 4" reinforced concrete at 12"o.c.. The slab is insulated from the ground with 2" of poly-iso close celled foam. He took the design from ones he had been installing in the Anchorage, Alaska area. He said he had done many of these, had never experienced any problems, and was certain we would be happy with the performance. The speed and skill with which he plumbed the system was proof enough to me that he was not blowing smoke up my very large skirt. What's the chance the patient will survive?

 

[Eric Johnson]

Not to butt into this highly informative and technical discussion, but it's my understanding that cold water returning to a gas/oil boiler that is not running (as in idled for the season) does not pose a corrosion risk. Seems to me that anyone with a Garn wouldn't really need a backup except for times when they're out of town for days and no one is around to tend the boiler.

Am I wrong on the low return water temp issue?

 

[Jim K in PA]

Slowzuki-Ya, I was thinking that he might already have issues with low return water temp into the propane furnace. I am curious as to what his return temps actually are, since I don't think the house is that big, despite the number of zones. If he is running 168 as the high set point, and assuming a 20 degree spread, his low set point should be 148. Given the "seat of the pants" design, delta T across the load side could be 10, 20, 30 or ? But, I imagine that his return temps are probably not causing an issue unless Robert is seeing rusty water disharging from his boiler drain(s). I personally am not familiar with the HX corrosion issue due to low return temps. Is water side corrosion, or combustion side?

With respect to the GARN keeping the return temps up, he could certainly mix the house side of the HX flow to keep that end of things happy. The GARN will not care about return temps on it's side. But, given Robert's budget constraints, maybe he could go simpler at first and omit the mixing valve. As to the high number of pumps, I like that approach primarily because it is discreet, and gives complete, seperate control over the districts. Three speed pumps will give him a degree of control without the expense of variable speed controllers/pumps, but then again, the delta T pumps from Wilo(?) apparently are not that much more expensive.

Eric - your input is never an interruption. I am still a newbie, but I have caught on pretty quick (I think ;-) ) You are correct - Robert's Burnham will have to be reset to a lower cut in temp so he can take advantage of the lower temps his slabs can use and the larger temp spread of the GARN.

OK - Robert - as Slowzuki said it is clear that you do not have a Mod-Con boiler. I guess at this point you have some decisions to make as far as design approach. Hopefully Slowzuki can take you in a cheaper direction than I did with the full-on P/S setup. Also, what kind of thermostats are you using? If you are using setback T-stats, in my opinion you should set them all to a consistant comfortable temp and leave them alone. With radiant the response time is not quick, and you really gain no economy with the setback. The thermal mass of the concrete slabs is slow to change temps. There may be a period of experimentation that you will have to go through to see if you can get by with lower water temps in your slab. If you can, this will give you more time between burns in the GARN. You can experiment without doing anything more than adjusting the Burnham's set point to between 130-150 and keep your T-stats at whatever temp you like (but constant). If you are still comfortable (and more importantly, your WIFE is still comfortable), then you can design a system that will use lower temps (mixing valve).

 

[rvtgr8]

The house is approximately 2,700 s.f. It has a steel frame with 8" cavity walls blown solid with cellulose. I sheathed both inside and outside of the walls with 5/8 OSB. The roof is concrete tile and there is a real wainscot of granite encircling the house. I have 39 dbl pane windows (low E) and have installed dbl walled polycarbonate interior storm windows on each. We have a Vermont Castings Reliant wood stove which we use to augment the home heating. We keep the thermostats at 60* year round. They are standard Honeywell (no frills) units. The house is incredibly efficient, not quite as efficient as our strawbale guest house, but pretty good nonetheless. We have Ponderosa pine firewood for free from our sixty acres. We are at 7,300 feet, with temps between 90* and -15*. Snows are brutal when they come and many years we have 160". We average between 1,400 and 1,500 gals. of propane for the entire year. Winter takes about 800 - 900 gals. of the total amount.

 

[rvtgr8]

I believe the settings are 128* to 168*. This is the gauge on the front of the Burnham with the boiler not firing. I believe the high end pressure is 30p.s.i.

 

[trehugr]

All I can say is WOW. What a beautiful place. If i come out to help you get hooked up, is there some good backcountry skiing nearby....duh...

 

[rvtgr8]

Tree.

Thank you for such a nice complement. My wife and I are retired school teachers and were only able to afford to buy such pristine land as a result of building everything ourselves. It is pretty sparsely populated and if we get a three foot snow, the cross country skis and snowshoes are the method of transportation of choice.
We love it here. We are greenies to be sure. We have the state's first bio-peat filtration system on our septic system. We are into ethanol production from switchgrass. We built a hybrid strawbale house for guests and are currently about to install a 24'x48' greenhouse (passive solar until the boiler comes into play) which we hope to irrigate with rainwater. I hope to invite people here for a chance to see what can be done with little money and a lot of hard work one day. More on that in the near future.

Robert

 

[rvtgr8]

Jim

I am not seeing any rust from my boiler, but if I wanted to do a more thorough check to see if I am getting internal corrosion, what would you suggest that I do? In terms of finance right now, I am hoping to buy and install this U-boat now for somewhere between $2500 and $3500. Is that unrealistic?

 

[slowzuki]

Hi Robert,
I think it is entirely reasonable to achieve what you want to do on the budget, the question will be how fancy to get with it, and how many of the other toys you want to hook in immediately. I've got a few questions for you about your current setup so we can help you more.

When it is cold out, do you know roughly what percentage of the time your circulator runs or zone valves run? Since you have basic thermostats I'm assuming it is wired to open the zone valve and start the pump or it may be wired to run the pump continuous and the t-stat just runs the zone valve.

Being its cold up there it may not be a problem, but if its warm, say from your stove, and no zones are calling for heat, do you have noises when a zone calls for heat? Some times happens when there is no relief valve between the manifolds from the zone valve slamming. This would be more common in shoulder seasons.

Once we figure this stuff out we can try to solve the plumbing.

I don't think you'll have a terrible problem with your gas boiler since its a high mass unit (cast iron hx) and you probably aren't using it to capacity. We just would like to do what we can to protect it. I assume right now you get your hot water off it with a coil?

Thanks,
Ken