My 2 story house has a heat loss 0f 43,000. Trying to decide which route I want to go, either something like a Tarm, a Varm, Vigas or Garn. Which set up, Garn vs others, would work better for my heat loss and using a forced air heat exchanger? Just curious if one of these type of units would work better than the other for those of us not fortunate enough to have baseboard/radiant heat. I'm planning on putting either unit in a boiler room in my detached garage, about 30' from the house. Thanks for your input.
Best boiler for forced air application
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maple1
Minister of Fire
I think generally the Garn is said to be better optimized when heating low temp radiant or the such due to its open design & need for heat exchangers, and I think also its tendancy to not stratify as well (not sure about that one). So interpolating that, it may not work as well as a pressurized boiler for doing a W-A HX for forced air. Aside from that, likely not much variance among the pressurized ones.
Coal Reaper
Minister of Fire
yeah, garn shines when its able to be used down to low temps. the problem with forced air and a garn unit would be if you let the supply temps fall for any reason, then you have to heat up the whole unit before you are able to get usuable heat for air exchanger. a boiler system with seperate storage will allow you to send heat to the house before it worries about bringing the storage back up to temp. after lighting, its a 10-15 minute response times vs. hours...
When my hot water temps get much below 150F with our forced air system the struggles to keep the house warm. In fact my pump cutoff temp is 155F. In our 5th year running without storage and love it, but I'm sure we'll love it more when our storage comes on line. For me installing and learning how to run the boiler in stages has been a blessing since as a DIY'r I had so many problems my first 2 years. I considered installing a Garn vs adding storage, but being stuck with forced air I got all the same advice as above. Your first 3 candidates have many happy owners here, but I'm surprised not to see Froling in the mix. My only 2 cents is to confirm that with forced air I need to run higher temps because of long duct runs etc.
I think you're going to see similar stories from us forced air guys regardless of brand of boiler. Plumbing does matter in these cases as you want to get the hot water to your loads before your tanks, if possible, when those tanks are cold. Other than some kind of measure of "time to achieve useable temp" I don't see how any brand would be better than any other when it comes to forced air.
For what it's worth you really can't compare a Garn to any other boiler operating without storage when talking about things such as useable temps and whatnot. Apples and oranges.
For what it's worth you really can't compare a Garn to any other boiler operating without storage when talking about things such as useable temps and whatnot. Apples and oranges.
As mentioned your ability to heat is limited to the 140 - 150 range. When you pick / size a water to air coil you want it oversized compared to sizing for standard system, so you can heat with these lower temps.
Coal Reaper
Minister of Fire
Would it be possible, after sending water through air exchanger, to then go through staple up in order to get more btus out before water goes back to storage?
Anything's possible, basement is unfinished. However, wouldn't I have a big temperature difference between the first and second floors?
So, in trying to heat with the boiler and forced air, are we burning more wood than our counterparts who are radiant or baseboard heat?
Coal Reaper
Minister of Fire
I havent a clue, something i know nothing about, just speculating. I want to figure out someway to add heated floors to my system. I have thought about a buffer tank on the return that radiant can pull from. Wouldnt know how to balance that with the baseboard or in your case forced air. I wouldnt look to heat the whole zone with that, just supplement.
Coal Reaper
Minister of Fire
No i dont think so. Btus in = btus out. Forced air is just not effective at lower temps so you will have to fire more frequently. If you storage were to drop lower you could go longer between fires but would need to have a bigger one to charge tanks all te way back up.
By saying more frequenty, are we talking maybe twice a day during the coldest days or more often than that?
Buzz Saw
Minister of Fire
You could then zone your forced air system. Zone down stairs and a zone upstairs. I think in order to zone you would just need to run a thermostat line upstairs and install the actual zone dampener in the duct work.
Buzz Saw
Minister of Fire
Coal Reaper, any clue what something like that would cost? Or what to use? I've been thinking about the same thing for my "new" 100 year old farm house I'm going be be buying.
Huh, I seem to recall some guys that had a forced air unit in their garage/shop and radiant for the house. FWIW based on advice here and in the Taco pump datasheet it was recommended to size the water to air HX for a ~30 degF delta T for in and out. The HX vendor gave me a HX thickness that fit in my plenum and just about nailed that 30 degF delta. During the recent vortex stuff our boiler was going wide open, never idling without storage. So in my case there just wasn't any excess energy to spread around. Someone would need to do some math to add up all the zone loads to size the boiler.
Coal Reaper
Minister of Fire
the extent of more frequently depends on the heat loss of the house as well as boiler size and storage. once you figure out how many btus your house needs per hour at design temp, then you can compare this to the size of storage you are thinking about with regards to the "usable" btus, i.e. 160?-190*. then i think most guys cut that btu/hr number just about in half to have an idea about what most of the winter might be like. nov/dec/jan i averaged 120#s/day of wood, but the few days when its below 10* that jumps to 220#s or more depending on the wind and clouds. i get 60-70#s in my boiler on a full load.
forget the second floor, you still have the forced air. i am thinking for applications where it is easy to access the first floor from the basement.
what it would take? i was thinking about a 100gal or so buffer tank that the return water flows through before going back to storage. a mixing valve (outdoor reset perhaps) and a pump would pull the appropriate water from this tank and circulate it through radiant loops. likely not the optimum system, but should be easy enough to do. i am interested in this not so much to actually heat the house, but to just warm the floors. my tiled kitchen is over the garage, wood floor living and dining room over unheated utility room (oil tanks, well tank, service, and pantry type storage), and tile/wood play room over finished part of basement that we keep at 60*. house is warm, floors are chilly. i would try to do three 300' loops i think. i could just rip the baseboard out but i think once in a while i would miss how quick they are to respond vs. the radiant. plus that would be a lot of patchwork with the floors and walls. again, havent really planned much of this out. i remember the post tennman is referencing, but i dont recall of anybody actually following through with such a setup. i am plenty open to suggestions and problems.
forget the second floor, you still have the forced air. i am thinking for applications where it is easy to access the first floor from the basement.
what it would take? i was thinking about a 100gal or so buffer tank that the return water flows through before going back to storage. a mixing valve (outdoor reset perhaps) and a pump would pull the appropriate water from this tank and circulate it through radiant loops. likely not the optimum system, but should be easy enough to do. i am interested in this not so much to actually heat the house, but to just warm the floors. my tiled kitchen is over the garage, wood floor living and dining room over unheated utility room (oil tanks, well tank, service, and pantry type storage), and tile/wood play room over finished part of basement that we keep at 60*. house is warm, floors are chilly. i would try to do three 300' loops i think. i could just rip the baseboard out but i think once in a while i would miss how quick they are to respond vs. the radiant. plus that would be a lot of patchwork with the floors and walls. again, havent really planned much of this out. i remember the post tennman is referencing, but i dont recall of anybody actually following through with such a setup. i am plenty open to suggestions and problems.
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