[CAUT] FW: Re: crack

[Ron Nossaman]

Fred Sturm wrote:
> On Jun 26, 2009, at 10:36 AM, Ron Nossaman wrote:
> 
>> Whatever it's called, the coils in the floor aren't radiant heat. It's 
>> convection, like the old also mis named radiators. Cold air sinks to 
>> the floor, is warmed by the floor, and little thermals break loose as 
>> the air warms, and rise up as more cold air pours in behind it from 
>> windows and walls. Radiant heat is just that. It's a heating element 
>> that isn't intended to heat the air directly, but warms everything in 
>> direct line of sight with it, which then warms the air secondarily. 
>> They are often used in large buildings, like hangars and auto shops, 
>> where there is a large air volume enclosed and big doors open 
>> periodically. You can stand 50 feet away from a radiant heater and 
>> feel it, even in below freezing air
> 
> 
>     I'm not an expert on the physics of heat transfer, but I know a wee 
> bit. The way I understand it, any material body that is "warm" emits 
> infra-red rays - radiates heat. That's how those night vision goggles 
> work: they pick up on those radiated infra-red rays.
>     Yes, the way a radiant heated floor gets the air in the whole room 
> warm is through a process of convection. But the air close to the floor 
> "picks up heat" due to radiation (it is warmed by absorbing infra-red 
> rays from the floor). It then travels up and is replaced by cooler air, 
> which repeats the process.
>     You could feel the radiant heat from a steam radiator, or from a 
> radiant heated floor, from 50 feet away, if the source were hot enough. 
> It's a difference of scale. Those industrial radiant heaters are awfully 
> hot and put out a lot of energy in the form of infra-red. So is a hot 
> wood stove. I believe the radiators or coils in the floor are usually 
> limited in temperature to around boiling (old steam radiators) or well 
> below (floors).
>     Maybe there is a physicist out there who wants to set us straight on 
> this.
> Regards,
> Fred Sturm

Air is heated in these systems by contact with a warm surface. 
A warm wall panel, floor, iron mass, or heat exchanger in a 
forced air system. A correctly named radiant heater doesn't 
try to heat the air, it directly heats distant objects by 
infrared radiation.

http://www.reverberray.com/
Ron N