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# Radiant infloor and baseboard heat

Member Posts: 2
edited February 13

I’m looking at building a tuck under garage style cabin on the Canadian border in Minnesota. 24x50 foot print of living area with a 16*50 lean to garage adjacent to it sharing the common wall. The grade level with thickened edge slab will be half living quarters half garage with radiant in floor heat . Second level will be all living quarters and planning on using hydro baseboard heaters up there . My question is does having the constantly heated area below change the btu calculations for the upper level. Im having a hard time finding anything on this . The garage area will have 1.5” foam on the undeside for insulation which is approximately 1/2 the grade level square footage . Appreciate the help.

• Member Posts: 7,818
edited February 13
When you have the Load Calculation completed for heating a particular room (whether it be Manual J or Hydronics Institute Form 22) the walls and floors and ceiling all need to be entered based on the fact that they are exposed to a conditioned space or not. If the wall or floor or ceiling has a conditioned space on the other side of it, then that surface is not considered as a surface that loses heat to the outdoor temperature. If the wall or floor to ceiling is exposed to a non conditioned space that that surface is considered as a surface that will lose heat to the outdoor temperature

So depending on how you calculate the heat loss the answer is yes or it might be no

I’m sure this is as clear as mud now

EDIT. Was a load calculation completed for the original home less the garage?

Then there may be some changes to the amount of heat needed for the rooms attached to the garage.

Also, are you going to heat the garage to the same temperature as the home?

Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
• Member Posts: 912
edited February 13
If the lower level will be continuously heated to the same temperature as the upstairs there will simply be zero heat loss through the floor of the upper level when you calculate the heat loss for that zone. The upper level heat loss will be just the walls, windows, roof and infiltration.

I assume though that the garage will be maintained at a lower temperature, in which case you would calculate the heat loss through that portion of the (well insulated!) floor of the upper level using the temperature difference between the garage and the upper level when occupied.

The same principles apply when you calculate the heat loss for the lower level; if the upper level will always be heated to the same or higher temperature there is zero loss through the ceiling.

Bburd
• Member Posts: 7,818
@tjohnsoncoatings said: I’m looking at building a tuck under garage style cabin on the Canadian border in Minnesota.

You want to be careful based on how close you are to the border. You may get some metric measurements and temperatures may be measured on Celsius on that radiant floor tubing based on where you get your material and documents. "Aye, Don't cha know"
Edward F Young. Retired HVAC ContractorSpecialized in Residential Oil Burner and Hydronics
• Member Posts: 23,272
Completely aside from the calculations... I'd have more insulation under that slab, and be sure to have perimeter insulation. Assuming it's not already built...
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 2
Thanks for the help it makes more sense now .
• Member Posts: 157
Why do we see so many houses with radiant first floors and baseboard on the second floor? Bite the bullet up front and put radiant on the second floor, use a propane fired mod-con and condense 100% of the time. If you insist on having baseboard on the second floor, put in enough to run low temps so the boiler can condense.