The best way to heat concrete?

August 17, 2007 8:20 AM

What is the best way to heat a 600 square foot concrete slab?

I need to install a heating system for a exposed concrete slab that will be in the living room of a new house. I've heard of both electrical and water systems but really know very little about each. I'd like to know the pros and cons of each system including cost, efficiency, and installation difficulty.

posted by CaptMcalister to home & garden (10 comments total)

If you use water then you can heat the water with whatever fuel is cheapest, and which likely is not electricity.
posted by caddis at 8:22 AM on August 17, 2007

The "This Old House" guys are constantly installing radiant heading systems. If you're pouring the slab (i.e. it's not already existing) then you can even have that built in.
posted by RustyBrooks at 8:26 AM on August 17, 2007

(That is, they are installing hot-water-based radiant heating)
posted by RustyBrooks at 8:26 AM on August 17, 2007

Hot water radiant flooring using PEX or another flexible tubing, there are lots of warm-floor style choices.

I would totally use a passive-solar-water-heater as well, should do you VERY well, and they're free after install.

Here's a good link: Water Heating

That site also has an excellent ebook available for download that tells you everything you need to do. Lifehacker just had an article yesterday from Instructables about a DIY PSWH system, although you would need more volume than that.

I would recommend indirect heating, meaning the water/glycol in the heater is closed-loop, and the heat is transferred to the floor water/glycol via conduction, so that the water in the closed loop remains as hot as possible for as long as possible.
posted by TomMelee at 8:33 AM on August 17, 2007 [1 favorite]

One word of advice about radiant heating. Put in a heat barrier between the floor and the ground! A friend didn't realize you had to do this, and his radiant heating is much more useless now that he's essentially heating the entire earth. (This should go without saying but apparently didn't.)
posted by salvia at 9:55 AM on August 17, 2007 [1 favorite]

HomePower magazine and the Journal of Light Construction have each done a few articles on radiant floor heating. They're both worth tracking down, even if you're not going to be doing the work yourself.

As Caddis said, use circulating water, then heat the water however you'd like. Electric heat is hilariously inefficient, and even with the discounts that power companies give to entice you to go this route, it's not cost-effective.

If you can possibly work a rooftop collector into the plan, solar water heating is much more cost-effective than solar photovoltaic, and since a radiant floor doesn't require a high temperature, you don't even need the expensive evacuated-tube collectors. Although a solar batch heater for the domestic hot water would be awesome too, and if you have any degree of concern for natural resources, I encourage you to investigate this avenue.
posted by Myself at 11:32 AM on August 17, 2007 [1 favorite]

Electric heat is hilariously inefficient,

Just to clarify, this statement is correct but you have to look at the whole process including generation of electricity. Most electric generating stations which use fossil fuels have an efficiency in the mid thirty percent range, with some new ones being perhaps a few percentage points higher. Almost two thirds of the energy in the fuel is thrown away as waste heat. Some plants recover some of this heat for industrial uses etc. but the vast majority just put it into the air or water. The actual conversion back into heat is nearly perfectly efficient, with some transmission losses etc. Nevertheless, you wasted most of the heat in the fuel creating electricity. Most fossil fuel based hot water boilers have efficiencies in the high ninety percent range. So if you burn the fuel yourself you waste much less of it. Of course, for most people the decision is based on economics not overall fuel efficiency. Nevertheless on a per btu basis, delivered to your door, fossil fuels such as oil or natural gas are typically much cheaper than electricity. Bottom line, if you are using electricity to heat you are doing the environment, and likely your pocketbook, no favors.
posted by caddis at 12:11 PM on August 17, 2007 [1 favorite]

Our own jdroth's website has been running a series from a man local to me about a housing renovation. In part four he promises that the subsequent week's Saturday post will be about a radiant floor heater. So you may want to check get rich slowly tomorrow.
posted by phearlez at 12:58 PM on August 17, 2007

. Most fossil fuel based hot water boilers have efficiencies in the high ninety percent range. So if you burn the fuel yourself you waste much less of it.


Genuine question, not snark: what about losses in transporting coal/fuel oil to you (private individual, individual delivery presumably using a fossil fuel drien vehicle) vs to a power plant?
posted by lalochezia at 3:00 PM on August 17, 2007

Thanks for the plug, phealez. That series is actually by one of my readers, a reader who -- in addition to remodeling his home -- is planning for his wedding. Translated: he hasn't submitted part four (about radiant floor heating) to me yet, so I'm not sure it'll be up tomorrow!

However, I'm confident that he will get me the info sometime soon, and the post will go up some Saturday in the near future.
posted by jdroth at 5:08 PM on August 17, 2007