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04-19-2010, 02:48 PM   #1
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## Electric radiant heat energy costs?

I'm thinking about doing tile with electric radiant heat in my kitchen remodel.

Is there any formula or rule of thumb for estimating the electricity costs to operate this?

04-19-2010, 04:44 PM   #2
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Very simple to compute the cost of electric radiant heat. Different companies supply different wattage per square foot, typical is about 10 watts per square foot. Assuming you have a 10 watt per square foot installation, the energy use per hour (in kw-hr) equals the area of the floor in square feet multiplied by the watts per square foot. So for example, if you have a 100 sf kitchen, you will use 1000 watts per hour, which is 1 kw per hour.

To figure cost, you need to know the cost per kilowatt in your area. I pay about 18 cents per kilowatt hour, but then I live in MA, very expensive power. Suppose you pay 10 cents per kilowatt hour, then it will cost you 10 cents per hour to heat that room. If you run 24 hours per day, it will cost you \$2.40 per day to heat the room, or about \$72 per month. If you run the heat 8 hours per day, the cost would be \$.80 per day, or about \$24 per month.

 04-19-2010, 06:50 PM #3 Member   Join Date: Sep 2009 Location: St. Paul, MN Posts: 91 Rewards Points: 75 Thanks for the reply, Daniel. The kWh * cost calculation is straightforward. What I'm more curious to know is what kind of wattage is required to heat a square foot of tile into the "comfort zone" in a room that's 65 degrees F. Many of these systems are thermostatically controlled, so they don't run 24/7. Also, even though I understand electric heat to be rather cost inefficient compared to natural gas, there would have to be some (minimal) reduction in gas usage with the radiant heat on. Any thoughts?

 04-19-2010, 06:58 PM #4 Member   Join Date: Jan 2009 Location: South of Boston, MA Posts: 17,248 Rewards Points: 2,000 My bathroom & hallway outside are heated by electric radiant I have 15w per sq ft to heat the area Most times I keep it at 65 & it does not go on that much We do kick it up to 72-4 when giving our son a bath There is an unheated basement (55-63) below & house is heated to 67-70 normally If this is located on a slab that will take a little more heat to keep the slab at a constant temp So wattage used will vary depending upon the installation & conditions
04-19-2010, 07:42 PM   #5
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Quote:
 Originally Posted by TomServo there would have to be some (minimal) reduction in gas usage with the radiant heat on.
100 cubic of NG = 100,000 BTU of energy = 29.3 kwh of elec. energy.

 04-19-2010, 08:42 PM #6 Tileguy     Join Date: Feb 2007 Location: Troy, Michigan Posts: 5,860 Rewards Points: 422 Many people keep referring to them as radiant heated floors. The heat mats or wires, are not made to heat space, they are made to warm the floor. No way they can keep a room warm. That's why they're correctly called warming mats. Jaz __________________ TILE GUY - retired- TROY, MI - Method & Product suitability consulting. MARBLE from ITALY & GREECE -PERLATO-PERLATINO-BOTTICINO-THASSOS-SIVEC-VOLAKAS-CALACATTA- NAXOS-Slabs-Tiles-Custom containers shipped to you - MARMO.SICILIA@yahoo.com
 04-19-2010, 08:46 PM #7 Member   Join Date: Jan 2009 Location: South of Boston, MA Posts: 17,248 Rewards Points: 2,000 I dunno about that I turn my bathroom up to 76 I guarantee you the room temp goes up And electric radiant heat IS used to heat rooms, large areas I have 15w per sq ft....at lower wattages it will not heat a room
04-19-2010, 10:14 PM   #8
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Quote:
 Originally Posted by Scuba_Dave My bathroom & hallway outside are heated by electric radiant I have 15w per sq ft to heat the area Most times I keep it at 65 & it does not go on that much We do kick it up to 72-4 when giving our son a bath There is an unheated basement (55-63) below & house is heated to 67-70 normally If this is located on a slab that will take a little more heat to keep the slab at a constant temp So wattage used will vary depending upon the installation & conditions
Did you notice an increase in your electric bill after installing the heating?

My kitchen is over a heated (but cool, 60-63ish) basement. The room is around 100 square feet, but I would only need to heat around 60 square feet due to cabinets and appliances.

 04-19-2010, 10:36 PM #9 Member   Join Date: Jan 2009 Location: South of Boston, MA Posts: 17,248 Rewards Points: 2,000 Our electric rates have gone down since the installation And I've replaced almost all lights with CFLs Plus we have a hot tub that we use in the winter Changed over to electric WH from oil fired after installation Added a larger pool pump And after it was installed our son was born, so house was kept warmer (oil heat) So very hard to answer that...too many thing have changed Nuheat has a calc to show cost to run per day: I have a different system but I used this to see approx cost, maybe 24c per day if I am heating ~56 sq ft @15c per kwh http://www.nuheat.com/sustainability...at-source.html 34 BTU's per sq ft is min needed to heat a room - 10w per sq ft I went with 15w per sq ft & 51 BTU's
 04-20-2010, 01:39 AM #10 Member   Join Date: Sep 2009 Location: St. Paul, MN Posts: 91 Rewards Points: 75 Yeah, I know its always tricky to determine usage of any one item without metering it specifically. \$0.24/day doesn't sound bad, though. My purpose is more to heat the tile to a comfortable temperature (maybe 12 hours a day, 6 months of the year), rather than actually heating the room. Maybe its not worth doing for that purpose. We have [unheated] tile in the main floor bathroom, and that doesn't bother me.
04-20-2010, 05:14 PM   #11

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Quote:
 Originally Posted by JazMan The heat mats or wires, are not made to heat space, they are made to warm the floor. No way they can keep a room warm. That's why they're correctly called warming mats. Jaz
So, not... correct.

The way to find out if you can use electric radiant as primary heating is to first complete a heat loss calculation for the space you want to heat. Once you have this figure in either btu's or watts, you compare it to the wattage (or btu's) the system will produce.

As an example: your room loses 5000 btu's of heat and hour. If you install a system that produces 4000 btu's, it will do a nice job warming the floor but be useless as a primary heat source. Conversly, install an 8000btu system in that same space and you have a primary heat source that will not only work efficiently, but recoup quickly. Then you do the math on cost efficiency and what it would take to do the same job with another heat (or radiant) source. Keep in mind that electric radiant doesn't cost anything to have if the tstat is not calling for heat. It also reacts faster because it can be closer to the surface and, there's no consideration for weight support, no maintenance...

That said, we don't recommend using line voltage elements or mat systems because of their use life. Though the system may produce all the heat you need, it would suck if in 11 years, it stopped functioning and your only recourse was to tear up the tile (or whatever flooring you have installed) just to replace the element. We recommend low voltage system with a 25 year warranty on the element...not prorated.
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04-20-2010, 08:06 PM   #12
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Electric radiant heat as a primary heating source is not typically cost effective in most of the U.S., as the cost per kilowatt hour of electricity is typically two to three times the cost per kilowatt hour for natural gas, and electricity is generally twice the cost per kilowatt hour than fuel oil or propane. The discussion gets confused because of differences in efficiency, and the fact that different fuels are measured using different units (i.e. gas is usually quoted in therms, and fuel oil in BTU's per gallon).

When you cut to the chase, electric heat is going to cost more than any other commonly used system. That said, I really like the heat in the kitchen, makes the tiles feel warm to the feet, and the cats like to sleep there when the heat is on. But of course we noticed an increase in the electric bill, you don't think the power company supplies free power?

Its all about your objective. If you want to save money, skip the radiant heat, invest in insulation. If you like warm floors and are willing to pay for the heat, go for it.

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