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Old 01-14-18, 11:44 PM   #1
Mukiwa
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Default Help me plan my DIY wood stove water heater

We are building a house with an insulated and hydronicly heated concrete slab as our floor and heat source. It will be heated with a propane boiler but I want to be able to hook it up to my woodstove in the future. Unfortunately the woodstove is not located beside the mechanical room so I have to run water line through the slab from the woodstove to the mechanical room. I will not be hooking up right away but I have to have the pipe in the slab before because once we pour the concrete I wonít have access to install a pipe later (obviously). What type of pipe should be used in the slab?

A few options:

Pex - Iím worried pex will melt with the heat of the woodstove,
Steel - I donít really want to have threaded fittings where I canít access them if they start leaking or something
Copper - $$$$$$

What would you use? And what size should the pipe be?

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Old 01-15-18, 04:41 AM   #2
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Pex. I think it's rated to something like 150įF at 100psi.
You could always make the first 5 or 10 feet out of copper incase of a rush of really hot water.
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Old 01-15-18, 10:47 PM   #3
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I wasn’t worried about the water temp but more the steel a loop running thru the woodstove conducting heat to the pex connection. How far away from the woodstove would the pipe get hot enough to melt pex... i am looking at the Hilkoil retrofit coil if anyone on here has any experience with this type of water heater.
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Old 01-17-18, 01:08 AM   #4
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Quote:
Originally Posted by Mukiwa View Post
Pex - Iím worried pex will melt with the heat of the wood stove,
I think your concerns are well founded regarding PEX and your wood stove. PEX has a maximum temperature rating of 180 F. After that it's bursting strength drops. I have seen photos of burst PEX that was used for solar collectors.

Your gas boiler probably has built-in precautions to make sure the PEX temp doesn't get to the danger zone. I have no information about what water temperature you will get from your wood stove. But you should be aware of possible problems. In my experience, the heat from a wood stove can vary quite a bit.

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Originally Posted by Mukiwa View Post
Steel - I donít really want to have threaded fittings where I canít access them if they start leaking or something
Steel buried in concrete will eventually have problems. History is on your side!

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Originally Posted by Mukiwa View Post
Copper - $$$$$$
Copper buried in concrete is not good either because of corrosion.

Best of luck,

-AC
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Old 01-17-18, 04:30 PM   #5
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So all my ideas are a no go lol.. Maybe some conduit buried under the slab with copper pipe inside... I would probably be ok with a copper-pex connection under the slab after 10-15’ if it was in a 3” conduit that I could pull out and fix if there were any issues.. I’m thinking 7/8 or 1” Copper depending on what size it come in. I don’t know if pex goes that big so I may even have to use polly
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Old 01-17-18, 04:34 PM   #6
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I’m pretty sure you only need 15-20 PSI for hydronic so I think over heating and bursting would be less of an issue but no one wants issues. I also don’t have endless funds and large diameter Copper isn’t cheap.. I probably have to go 25-30’ from the woodstove to the mech. room which isn’t ideal but it is what it is.

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