tankless for radiant heat?

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Old 11-01-07, 11:29 AM
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tankless for radiant heat?

I would like to retrofit my old house with an under-the-floor radiant heat system. I am getting both "yea" and "nay" for using a tankless hot water heater with the system. It would be heated with propane.

Can a tankless keep up with the demand in Central Illinois winters? Or would a bigger tank style be better, like say 80 gallons? It would only be used during cold weather, and I already have a 50 gal. electric tank for my regular hot water supply.

I'm looking for an economical approach here, so I'd rather not have to get a whole-house boiler type of system.
 
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Old 11-01-07, 01:33 PM
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That is a tough call. If you go tankless, your unlimited on capacity, but if you have a BIG load, it could take quite a while to overcome it. You would need to size it right and make sure you get one that has a large Delta T. If you get one with a small one, you could be shooting yourself in the foot.

Now, having a big water heater is nice because you'll always have capacity readly made in the form of 80 gallons of hot water. But, under a big load, your house could start to get cold since the recovery time might be a while.

Do your homework and make sure you double check your numbers!!
 
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Old 11-03-07, 02:13 PM
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This will sound very opinionated but I think that using a tankless for heat is pretty hackish and shortsighted for two major reasons. The heat exchanger is restrictive and it lacks proper controls.

The heat exchanger works great with your home's water pressure of 40 to 75 pounds but when you're circulating heating water through using a pump, your gonna need something specialized to pump enough GPMs through such restrictive passages. Price a Taco 014 and compare that to a 007. And unless it's a closed system, those pumps need to be bronze or SS.

So how are you going to control the tankless to heat the house? A good modcon will have built-in outdoor reset and on a single zone system just needs a t-stat and would be far far more efficient on fuel.

I'm not saying it can't be done, but the savings aren't as big as they might seem and it may create issues when you sell or if your insurance company finds out that you're heating with an untested/unapproved device.
 
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Old 11-06-07, 06:23 AM
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Thanks to both of you for the input. Great points all, and a lot to think about.

I suppose a small boiler, like the Munchkin types are a good choice for radiant heat, but they are so high priced and from what I have read online, don't last as long as they are supposed to (no one seems to get the 20 years they claim, and repairs seem to be a problem). If I'm going to replace the water heater every 10 years anyhow, I might as well get the traditional big tank type and save the $1500 or so I'd have to spend on a boiler. It's only for use 4-5 months per year anyhow, and I'd be supplimenting the heat with a corn or propane stove--partly for heat, partly for atmosphere.

Thanks again.
 
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Old 11-06-07, 06:43 AM
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Better check code in your area. You may not even be allowed to use a domestic water heater for home heating.
 
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Old 11-06-07, 12:29 PM
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The tough part is that modcons are still relatively new for North America so their prices are rude. In Europe they are far cheaper. Once it becomes more of a commodity product the profit margins can come down to reality.
 
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