If Warm Air Rises...

Mike T., Swampeast MO

...and radiation "radiates" and the floor-ceiling temperature temperature difference in a radiantly heated space is low then why does the ceiling loose multiple times more heat than the walls?

hr

I think

the windows are still the greatest loss area. I also feel the ceilings run more thanm just a couple degrees warmer than the floor level.

I worked on a tall radiantly heated home a few years back. An electrician was installing the trim on the light fixtures. He was sweating pretty hard. I told him it is only a few degrees warmer up there than where I was working.

He said climb up this ladder and tell me that. While I didn't have a thermometer with me, it sure was a lot warmer than I had imagined up there. Definitaly not the 2-3° you see advertised

hot rod

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Bob Gagnon plumbing and heating

???

i just bought a laser thermometer and brought it to a house i did radiant in with 18' ceilings, where the carpenter said it was a lot cooler up there, and it was 70 degrees at eye level everywhere, even the outside walls, but cooled as you went up. it was 57 degrees at the ceiling. my house with low ceilings there was no difference. bob

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S Ebels

Could be

The difference between your the two systems was how closely the floor output actually matched the heat loss of the structure. Modulating water temp based on outdoor reset typically runs a lot tighter temp wise. I see way to many radiant jobs controlled by a bang-bang t-stat with fixed water temps.

Mark Eatherton1

Could also be...

an influence of solar gain causing hot air to rise. In every case where I've used my infrared to check ceiling temps on RFH projects, they're ALWAYS cooler than near floor level temps, except where there is significant solar gain, or other air heating means heating the air currents.

ME

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rod robbins

insulation

hello
This thread made me think of a question.I am building a new home with radiant floors and the insulation has been instaled to R38.The contractor want to put a few more inches to bring the R factor to 45.Since the temps are not rising is it a waste to insulate the ceiling so heavy?
Rod

Weezbo

rod guy with the insulation question...

insulation basically slows the heat down on its journey to cold. In alaska if you say you have r-19 in the ceiling and r-19 in the walls the first order of the day is Insulate! if you are building a new home or addition foam board under the slab around the perimiter walls and on the Flat around the perimiter is a Normal building practise...and that is on the ground my ceiling has r 71:) i dont care what "they" say:) when "they" are buying the fuel oil for my home, i will make the walls out celophane oh twenty years ago we were building outside walls with r-32 on some of our jobs and there were others who went to high mass and double wall construction techniques .insulation is the most economical placement of effort and $ your guy says pump it ($'s)in the ceiling and walls and yes even the ground...better that then over and done with than many a $ wheel barrowing its way to your favorite oil company.... oh if you live in warm even Hot climates dont worry insulation works well there also....one working vacation many years back i put a roof over a roof with mucho insulation and white grey roofing in north carolina the building inspector thought my father was MAD )) well let me say insulation and ventilation work wonders on the air conditioning bills too! he was way suprised that we didnt have the air conditioner on )) gave the guy something to think about:) and as much as the inspector thought some black roofing would look better my father had to defer to my insistantce on white or grey:)in front of the inspector just to keep the guy from feeling demented.the guy figured it would make the place Hotter...must be the heat from the sun is all my dad could think of saying in the guys defence.

Rudy

Warm air doesn't rise...

Hot air rises. When you can heat a space to 70* with 75* floor surface temp how much convection occurs. Not much I would say. Cooler near a high cieling with rfh kind of makes sense.

hr

I'm not sure

an IR lazer thermometer is the best way to measure air temperature at the ceiling. Doesn't it read the surface temperature of what you point it at? If you point it at the ceiling sheetrock, for instance, and it reads 65°, wouldn't that be the sheetrock temperature and not necessarly the air temperature at that point.

I know running floor slabs at 85° doesn't always equate to 85° air temperatureat the floor level.

Seems the better way would be to hang an air sensor thermometer below the ceiling?

hot rod

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