Quote:
Originally Posted by Porsche-O-Phile
I've seen PEX used to do fairly long runs of heating water from heat pumps to area heaters - my understanding is that it affords very good insulation to the fluid inside - for this reason I don't think it would necessarily make a very good "radiator" to transfer the heat from the fluid to the slab (through the wall of the tubing). Maybe there's a way this is dealt with in those particular applications but I'm not familiar with it (would have to check). I've dealt with heated driveways which always used metal or copper piping and typically would introduce corrosion/failure loci at the penetration points (although there are probably ways to detail this to prevent it from decaying in those areas)
You might be right though - if you have a well-insulated living area and are relying on a heated slab, the cost might be less to run the associated water heater or heat pump than to run a furnace - it costs a lot (and is inefficient) to heat up a lot of air to blow around - but it is also easier to control space-by-space which is why it's typically done in large installations (VAVs, etc.)
I'd have to see a comparative analysis but my gut feeling is it'd probably be a toss-up with respect to operating cost versus a "conventional" forced air system which throws it back in the court of construction cost - probably a lot cheaper to do a ducted forced air system than a heated slab (especially if you're talking about more than one floor!)
If ya got the money though... I love the idea of radiant flooring. The quality of the heating is awesome.
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I have had both a Wirsbo (hot water) system and an electric cable system in a poured basement slab. I had them built in both cases.
The electric cable ran $1 per square foot, installed plus the extra washed sand and rigid foam insulation around the perimeter to create the thermal mass. It was on a seperate box and meter, and our electric company had a special rate for off-peak (and even had a rebate program that almost paid for the system). It would kick on at 6pm (if needed) and run until 6am (if needed). It was toasty and took the temperature of the slab (not the air). It cost about $15 per month during the winter months and made the basement (esp the bathrooms!) much more liveable.
The hot water systems are more mainstream. They are straightforward and easy to install. They can be run with hot water heaters, or specialized heavy-duty hot water heaters, or dedicated boilers. Since PEX is designated for potable, the entire system could be integrated with your regular hot/cold plumbing. Even after going through the heating loop the returning water was still warmer than from the street, cutting down the energy needed to generate more hot water. Incorporating a geothermal heat pump and/or an auxillary external wood (or whatever) boiler can really save.
Also, if you have tall ceilings or great rooms or large vaults or open staircase, heating the floor (rather than the volume of air) makes sense.