# radiant infloor heat??



## StackedLumber (Apr 15, 2010)

With radiant heat on a concrete slab, a friend was telling me that the air gets significantly cooler as it gets higher up in the room.  This person was justifying (arguing) not having adequate insulation (R-26 instead of R-38) in the attic b/c the air was getting cooler at it reached the ceiling.  He said it was like thermal stacking in a water heater.

I don't buy it . . . heat rises and in my pea brained mind, the more insulation up there helps keep the heat down in the building and keeps the cold out of the building.  Looking for some help from the experts


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## Hunderliggur (Apr 15, 2010)

Yes, heat rises.  Radiant heat heats the objects (the floor and furniture) not the air.  You will feel the warmth through the floor.  You should have adequate ceiling insulation regardless of the type of heat.  He may be loosing a lot of heat at the ceiling causing the coolness.  The air will circulate downwards eventually.  I have radiant throughout our house (both floors) and have not noticed it being cooler when I stand up!  My storage tanks straify but it is the hot on the TOP, not the bottom.


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## jharkin (Apr 15, 2010)

Agreed.  You are right.


Your friend can believe what he wants but it wont change the laws of physics.  Warmer air is less dense which is why it rises  - the exact same effect that causes draft in your flue.  If he has limited ceiling insulation the ceiling may feel cooler than the floor, but that is cooling the air which will fall back down to the floor to be warmed again and then rise back up - causing convection currents.


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## Hunderliggur (Apr 15, 2010)

You can also feel radiant cooling.  If the ceiling is cooler the "air" will feel cooler.  If you have an IR thermometer you can measure the floor, wall, and ceiling to see the difference.  My IR Thermo doesn't work after it went through the washer :-(


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## benjamin (Apr 16, 2010)

Yes, of course it will be cooler higher up, so when you sleep naked clinging to the cieling fan you won't be very comfortable.  

I've heard people who complained about their feet getting too hot working in workshops without enough insulation, the floor feeling cold if there is too much insulation, and the whole radiant infloor heat thing being unnecesary in a well insulated building, but I have never heard anybody say that the air temperature variation was a weakness of infloor heat.

Or is he saying that you want it to be cooler higher up? Cooling the cieling will cause the floor to maintain a higher temp to keep the average the same. If you want bi-level heat that may be the simplest way to get it, but I agree that it's not worth it.  Is this guy a full bearded nudist or what?

If he's saying that you don't need the insulation because the cieling will stay cool, he's partly right, but when the cieling is cooler than the floor it's because there is a lot of heat loss keeping it cool, if it's well insulated/sealed there won't be as much difference in temperature between the floor and cieling.


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## ihookem (Apr 16, 2010)

I know that  you get a draft in a poorly insulated house because the cold ceiling might be cooler than the floor on the ground. Then you get cool air sinking and warm air rising. It feels drafty and can feel cooler air moving and cold spots. This is why good insulation is so important. It makes the house much cozier and can even feel as warm when the room temp is a few degrees cooler.


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## dave11 (Apr 16, 2010)

Sorry to have to disagree, but there is some truth to the idea that rooms heated via radiant floors do not need the same amount of ceiling insulation to be comfortable. 

The radiant heat coming up from the floor will travel in straight lines until it hits something with more density than air. That would be furniture and other solid items in the room, including people. Those solid objects are heated radiantly, not by convection, and they will feel warm because of the floor. It's true that a cold ceiling can make the room feel colder, same as a cold window will do, but because it is so much farther away than the floor (unless the ceiling is very low), the effect is much less. 

Incidentally, the more furniture or people in the room, to absorb the radiant heat before it gets to the ceiling, the better efficiency he will have.

Of course, higher R value in his ceiling would help retain some slight additional heat, but it probably would take 50 years to recoup the cost of that insulation. 

Incidentally, only hot air rises. Heat itself moves in all directions equally, from warm to cooler.


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## StackedLumber (Apr 16, 2010)

I don't think he's a full bearded nudist or anything, I just think he's the type to get out of spending money on stuff that in his mind he shouldn't have to.  You ever meet those kind of people, buy every thing cheap over and over and over again, instead of buying it right the first time?   

I just can't seem to understand the reasoning that he says and his exact words are "the heating experts say" that the cooler air weighs down the warmer air to keep it near the bottom.  Full of bull if you ask me.  He also said that w/ radiant floor heat the ceiling is the coldest part of the room . . .again I don't buy it, but some may argue against it.  

Sometimes the proverb is true-if you argue w/ a fool . . . .


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## dave11 (Apr 16, 2010)

StackedLumber said:
			
		

> I don't think he's a full bearded nudist or anything, I just think he's the type to get out of spending money on stuff that in his mind he shouldn't have to.  You ever meet those kind of people, buy every thing cheap over and over and over again, instead of buying it right the first time?
> 
> I just can't seem to understand the reasoning that he says and his exact words are "the heating experts say" that the cooler air weighs down the warmer air to keep it near the bottom.  Full of bull if you ask me.  He also said that w/ radiant floor heat the ceiling is the coldest part of the room . . .again I don't buy it, but some may argue against it.
> 
> Sometimes the proverb is true-if you argue w/ a fool . . . .



The reason the ceiling is, in fact, colder than the floor, is because the heat is coming through the floor, in the form of radiant energy. It does not heat the air. It travels, like light, upward toward the ceiling. If it contacts a solid surface first, that object will be heated. That's the difference between radiant heat and convection heat. But because at least some radiant energy will hit the ceiling, and be lost to the attic, the ceiling should be insulated. More is better, but there comes a point where the money is not recovered. But it's true that the ceiling will always be the coldest part of the room.


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## benjamin (Apr 16, 2010)

StackedLumber said:
			
		

> the cooler air weighs down the warmer air to keep it near the bottom.
> 
> He also said that w/ radiant floor heat the ceiling is the coldest part of the room . .
> . . .



At first I thought he wanted it cooler near the ceiling, now I get it.  

I don't know if the "air weighs down" but the air circulation isn't that big of a deal because the temp difference isn't that big, also because the air temp is typically lower for the same comfort level. 

I disagree that the ceiling should be the coldest part of the room, typically there is far more insulation in the ceiling than in the walls, and it's not because hot air rises, it's because it's cheaper to add extra insulation in the ceiling than to add insulation to the walls or windows.

The extra cost of going to R-60 in a typical attic is so small ($.20 /ft) that it will pay off in a short time even if you burn wood, unless of course the rest of the house is so bad that the attic is already an insignificant part of the heat loss. 

His facts are correct, but I don't agree with the conclusion.


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