Supplemental heat to wood boiler heating radiant floors
Last Post 08 Dec 2018 01:16 PM by hambone. 3 Replies.
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hamboneUser is Offline
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07 Dec 2018 10:56 AM
I have a 1400 sq. ft. apartment in central Maine in a renovated barn with radiant floor heating. The floors downstairs are concrete and upstairs wood. A Tarm gasification boiler with 820 gallon storage tank is used to heat the floors and DHW. This system was designed by professionals and the total heat load is 40kBTUs/hr. It is a passive solar design so when the sun shines it helps but it doesn't shine a lot in the winter. I have been very happy with the system but I would like to leave for a week or two and I'm looking for a back up system, any recommendations would be appreciated.
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07 Dec 2018 07:07 PM
If you have a big enough power service a 12 kw electric boiler could deliver the full 40 KBTU/hr. It would require a dedicated 70A/240VAC breaker (and suitably fat wiring) to support the boiler.

A load of 40K seems like quite a lot of load for a 1400' apartment even at -10F (or whatever the local 99% outside design temperature is.) Current code-min houses would usually come in at half that or less, but perhaps the high peak load due to excessive glazing for the passive solar(?)
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07 Dec 2018 08:46 PM
My concern would be not having the HR system freeze while away. Using propylene glycol in the system could mitigate that concern. If, as Dana suggested, an electric boiler is an option, you might want consider using a NextGen boiler which is actually a fully automatic plug & play HR appliance that contains everything necessary to fully operate your HR system (e.g., control system, differential pressure valve, expansion tank, and pump). You could just plumb the NextGen so it could be isolated from your existing manual system. Cost is about $1,200 and you would want their NextGen-12 model (12 kW or 40,956 Btu/h) if your numbers are correct, but perhaps you don’t need that much while away (i.e., perhaps you don’t need DHW and as high an indoor temp setting).

http://www.nextgenboiler.com/
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08 Dec 2018 01:16 PM
Thank you for your replies. I like the idea of the simplicity of a plug and play electric boiler. I will try to address the questions about the 40K heat load. You know when you build you research and research and then pick a plan. Well when we were deciding on insulation under the slab we thought the way to go was with the bubble foil insulation and then right after the pour we realized that we should have gone with the tried and true rigid foam insulation. We tried to save ourselves by insulating the perimeter with rigid R13. Our other numbers are downstairs concrete floor R2 and upstairs R14 wood floors. Ceilings, downstairs R10, upstairs R30. Walls R11, spray foam in full 2x4 studs. And yes I would say the south side passive solar is a heat loss at night even though we have shades. It is about 40% windows. Anderson windows R3.
The average BTUs/sq.ft. is 27. Outdoor design temp:-8deg.F. and located in cold central Maine. Again thanks. Hambone
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