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#1
01-04-2010, 06:12 AM
 JohnFRWhipple Bathroom Renovator Join Date: Jan 2010 Location: North Vancouver Posts: 1 Rep Power: 0
Calculating the BTU/hr rating of Electric Cable Heat

I found another website describing the heat output of cable heat electric flooring with a 3" standard spacing to be 34 BTU'S per square foot.

Rather than trusting this site the cable heat kit I'm going to use is from Warm Tiles (240 Volt DFT 2065 60-70 sq feet 3.3 Amps).

Can you covert Amps to Btu's per hour? Just found this thread here.

"Btu is a unit of energy not power, not sure why you would need Btu values. Usually things like backup power supplies are rated in Watts or kilowatts.

But here is how you would do it.

Amps * Volts = Watts
Watts * hours = watthours
watthours * 3.41214148 = Btu

So you would need to know amps, volts (usually 120 or 240), and the number of hours."

With this math I get 3.3 Amps X 240 Volts = 792 Watts
792 Watts x 1 hour = 792 Watthour
792 Watthour x 3.41214148 = 2702 BTU

With the rate of 34 BTU's per square foot I get 2210 BTU's

Which one is right? Is it possible the 19 % drop is allowed for the heat loss through the setting material and tile?

Thanks,

John Whipple
By Any Design Ltd.

"When it's perfect. It's good enough."
#2
01-04-2010, 09:23 AM
 JohnS Moderator Join Date: Dec 2007 Location: SE Michigan, USA Posts: 9,535 Rep Power: 19
Re: Calculating the BTU/hr rating of Electric Cable Heat

Quote:
 Originally Posted by JohnFRWhipple I found another website describing the heat output of cable heat electric flooring with a 3" standard spacing to be 34 BTU'S per square foot. Rather than trusting this site the cable heat kit I'm going to use is from Warm Tiles (240 Volt DFT 2065 60-70 sq feet 3.3 Amps). Can you covert Amps to Btu's per hour? Just found this thread here. "Btu is a unit of energy not power, not sure why you would need Btu values. Usually things like backup power supplies are rated in Watts or kilowatts. But here is how you would do it. Amps * Volts = Watts Watts * hours = watthours watthours * 3.41214148 = Btu So you would need to know amps, volts (usually 120 or 240), and the number of hours." With this math I get 3.3 Amps X 240 Volts = 792 Watts 792 Watts x 1 hour = 792 Watthour 792 Watthour x 3.41214148 = 2702 BTU With the rate of 34 BTU's per square foot I get 2210 BTU's Which one is right? Is it possible the 19 % drop is allowed for the heat loss through the setting material and tile? Thanks, John Whipple By Any Design Ltd. "When it's perfect. It's good enough."
You can also write the conversion from electrical data as
watt * 3.41214148 = Btu/hour. The conversion from electrical power is correct.

The 34 BTU (per hour) per sq ft is a recommendation or design goal on how much cable to install. The stated 60-70 sq ft is not entirely consistent with the above, I get 2702 BTU/h ÷ (34 BTU/h/ft²) = 79.5 ft².

As long as there is a thermostat to turn it off when the room is warm enough, it will make little difference. A little higher BTU/h/ft² will give a little faster warm-up.
#3
01-30-2010, 12:39 PM
 james goiu Guest Posts: n/a
Re: Calculating the BTU/hr rating of Electric Cable Heat

this the formula i use for lp gas or nat gas, 35 btu per squr ft, 20 btu a squr ft for a/C.
#4
04-07-2010, 07:46 PM
 Unregistered Guest Posts: n/a
Re: Calculating the BTU/hr rating of Electric Cable Heat

The voltage could be 230V or more or less, by a bit.
The cable could cover 60 or 70 square feet, give or take.

It's all in a range.

johnfrwhipple, your first post mentioned a value and referred to an unknown source, without stating whether that 3" cable was a 230V or a 115V system.... To get a handle on the issues, ya gotta be precise. (man!) Since your next sentence dealt with a 230V cable, we might assumer you got it right. Or not.

hth
-d

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