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Posted by S. Barker on April 3, 2008, 1:15 pm
BUT, only one thing wrong with this statement about the cold floor.
Insulating the floor will not make it warmer, 'cause the 'cold' does not
come from below. The only way to make a floor warmer is to put heat UNDER
it. Heat rises, cold falls. can't change that.
s
>> Yes, but insulating a floor never pays back. It's a waste of time and
>> money.
>
> Based on what time and energy cost assumptions are you basing that
> particular gross generalization? I'd imagine that floor insulation
> life would be on the order of several decades, and unless you've got a
> Mr. Fusion cranking away to keep you warm, I doubt that energy costs
> are going to go down in the foreseeable future. There's also the
> issue of comfort. A warmer floor is more pleasant to walk, keeps your
> whole body warmer, regardless of time and money invested, and cuts
> down on drafts - a major source of heat loss and discomfort.
>
> R
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Posted by dpb on April 3, 2008, 1:19 pm
S. Barker wrote:
> BUT, only one thing wrong with this statement about the cold floor.
> Insulating the floor will not make it warmer, 'cause the 'cold' does not
> come from below. The only way to make a floor warmer is to put heat UNDER
> it. Heat rises, cold falls. can't change that.
...
Except it isn't so...warm, _still_ air rises, not heat.
Heat conduction is independent of anything except h, A, and dT and knows
nothing of direction--at a given delta-T, the same amount of heat is
conducted out a wall or ceiling of the same area and w/ the same overall
effective heat transfer coefficient and temperature differential. And
the temperature differential is dominated by the effective k which is
insulation value.
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Posted by RicodJour on April 3, 2008, 1:43 pm
> S. Barker wrote:
> > BUT, only one thing wrong with this statement about the cold floor.
> > Insulating the floor will not make it warmer, 'cause the 'cold' does not
> > come from below. The only way to make a floor warmer is to put heat UNDER
> > it. Heat rises, cold falls. can't change that.
>
> Except it isn't so...warm, _still_ air rises, not heat.
Why do you say that it's only still warm air that rises? Any body of
warm air rises and induces convection - sailors have been relying on
it for millenia. Since convection is a more efficient heat transfer
mechanism, it seems a bit misleading to say that heat doesn't rise.
R
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Posted by dpb on April 3, 2008, 2:46 pm
RicodJour wrote:
>> S. Barker wrote:
>>> BUT, only one thing wrong with this statement about the cold floor.
>>> Insulating the floor will not make it warmer, 'cause the 'cold' does not
>>> come from below. The only way to make a floor warmer is to put heat UNDER
>>> it. Heat rises, cold falls. can't change that.
>> Except it isn't so...warm, _still_ air rises, not heat.
>
> Why do you say that it's only still warm air that rises? Any body of
> warm air rises and induces convection - sailors have been relying on
> it for millenia. Since convection is a more efficient heat transfer
> mechanism, it seems a bit misleading to say that heat doesn't rise.
Because in a circulating system the circulation pattern is generally
stronger than the convective force...
But the point is it isn't "the heat" that is rising, it is that warmer
air is less dense and hence does tend to rise. But, as the assertion
made here again is also misleading at best, it's important to note that
it isn't "heat" that's moving somehow magically out the ceiling that
leads to the perception that floor heat loss is somehow magically different.
--
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Posted by dpb on April 3, 2008, 3:13 pm
dpb wrote:
> RicodJour wrote:
...
>>>> ... Heat rises, cold falls. can't change that.
>>> Except it isn't so...warm, _still_ air rises, not heat.
>>
>> Why do you say that it's only still warm air that rises? ...
And, I didn't say "only", I simply emphasized "still" owing to the
effect as noted earlier being most significant when forced convection
isn't in play.
And, of course, while convection is effective in heat transport within
the room, once it gets to the wall/ceiling/floor surface, except for
undesirable leakage paths it becomes a conduction problem for the most part.
Hence, except for the probably relatively small (in general) temperature
difference in a well-regulated room between the ceiling and floor the
heat loss is pretty much dependent on how cold the other side is and the
effectiveness of the insulation.
Of course, there's the sensitivity of bare skin to hard floorings issue,
too, that is a localized heat transfer effect, particularly to bare feet. :)
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