Cold rooms over the garage. Already insulated as best can reasonably be done. Thinking about adding radiation to the rooms above.

Garage is a two-car "tuck under" built into the side of a hill. It's got two concrete side walls (24Lx8H, 8" thick, poured) and a concrete floor (~24x24, unknown thickness, probably 3-4"). Third wall adjoins an unheated basement.

The frost line is 4 ft, so ~half the height of the walls would be below frost line and presumably at least slightly above freezing. The floor is technically below the frost line, but since it abuts the lower grade, I assume there's an above-frost-line component that is effective some distance into the garage.

The question is how to treat this space for heat loss calcs so I can size the radiation appropriately. I'm presently using Slantfin's HE2 software and specifying the heat loss for the rooms over the outboard 12 ft of the garage (bedroom, closet, small bath) using floor insulation criteria that amount to ~R30 since that's what's there. I get a total design heat loss of ~6000 BTU/hr for these rooms. Presently have ~8500 BTU/hr of radiation, so obviously there's something missing from the loss calc.

Any insight appreciated. Thanks.

 

You have radiation with a capacity of 8.5K but how much are you getting out of it? Is the stat in an area which is overradiated? Is the calculated heat loss based on "over an unheated crawlspace"?

 

Stat is in an area that has radiation comparable to heat loss. Rest of the zone works fine based on that stat. Seems like we're just not putting enough heat into this space. FWIW these rooms are only the second and third pieces of element on this loop, so the supply temp is still pretty high.

Heat loss calc is based on "over unheated space" and actually I've done it with "over exposed space" (which in slantfin-speak makes it 0.01 more "lossy") with the intent of overestimating loss, if anything.

Thinking here that with near-constant circulation, and xx more BTU/hr radiation to be determined, the room gets closer to input=output because presently it feels like it's running a deficit. These rooms were previously lightly used so we just kept the door closed and didn't care about the temp. Now they see heavy use and the underheating is readily apparent.

 

"...presently it feels like it's running a deficit."

I'm sure you have actually measured the temperature in the "cold" area. Do the fins have an adequate gap to the floor covering? Can you measure the temperature drop thru that run of baseboard?

 

Lately, it's 2-3F colder in this area compared to the rest of the zone. It should get worse as winter progresses, if memory serves. Fins/gap/etc. all nominal. Even vacuumed/brushed them the other day. Will measure deltaT tomorrow.