Radiant electric floor heat - DIY Chatroom

chatroom3542 · 10-19-2009, 05:34 PM

Does anyone know the cost per hour of running those mat type floor heaters under tile bathroom floors. I know it depends on the size of hte room and the local utility. Guess I'm asking if I leave it on for several hours if I'll need a second job to pay the utilities. Is there anything else effective for the $$

Thanks
Laura

poppameth · 10-20-2009, 12:19 PM

From what I recall, most of them claim to cost only pennies a day to operate. They are mostly low voltage systems now. Warm Tiles says 1 cent / sf / day is the average cost. So a 50 SF bath would be $0.50 / day to heat.

warmsmeallup · 10-24-2009, 09:22 PM

It's not the square footage, it's primarily the wattage output of the element you use. It's a simple calculation:

If the product output is 15 watts psf and you cover 100 square feet you are using 1500 watts (or 1.5 kilowatts) of power per running hour. Take what you pay per kilowatt hour and multiply the total kilowatts (1.5 in this example) times what you pay:

1.5 x $0.10 = $0.15 per running hour.

Any other questions...don't hesitate to ask!

Daniel Holzman · 10-25-2009, 12:18 AM

I don't think I understand the comment by warmsmeallup that "Its not the the square footage." The power output stated of 15 watts per square foot is consistent with other manufacturers, and the mathematics showing that you multiply the area in square feet by the power per square foot to calculate the number of kilowatts per hour is correct, so obviously the critical factor in the cost is the total number of square feet you are heating, the cost per kilowatt hour where you live, and the percent of the time you are running the system.

In my house, the system runs about 30 percent of the time in the winter. I live in the great state of MA, which has about the highest electric cost in the nation, at about 18 cents per kilowatt hour. I have 140 square feet of floor area. So, 140 sf x 15 watts/sq ft = 2.1 kw x 18 cents/kwh is about 40 cents per hour x 7 hours per day = a little less than $3 per day. I happen to like the heat on my feet in the kitchen, but this is far from the pennies per day advertised, unless you think 300 pennies per day qualifies.

warmsmeallup · 10-25-2009, 10:31 AM

Hey Dan:
15 watts is not a standard. We install systems with variable voltage outputs thus, varied wattages psf. We install floor warming systems that only need to generate 8 watts psf to warm the floor while primary systems can require 12-15. We just completed a bathroom that required 21watts psf. Whatever works! Thus, the varied costs to run psf. Yes, the cost of electricity + running hours adds to the calculation but the variable in cost per running hour is the watts psf required.

I completey agree that you have one of the highest rates in the nation. Sorry to hear that. I would never say that a professionaly installed heating system (of any kind) costs pennies a day. That's some of the manufacturers words. In your application, I would not recommend an electric system as primary unless you had no other choices.

What type of insulation do you have under your radiant? 7 running hours a day is relative. What temperature do you set your tstats to? We have 3 separate systems in my home and our kitchen is 180sf. My system only runs 3-4 hours a day with floor temps of 78 ($0.16/Kva) but we turn it down when no ones around. I installed a reflective barrier 1" off my subfloor between the joists below with R-13, 1" below that with a cold basement.