gas hot water heat for hydronic floor heat


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Old 06-10-24, 04:16 PM
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gas hot water heat for hydronic floor heat

I have used an outdoor boiler for my heat for over 20 years but i am going to convert to gas as i am getting older. My old Out door boiler was open to atmosphere and produce very little to no pressure
I am going to use a gas hot water heater and am wondering if i need to lower the city supply line to 10 or 20 psi when filling the system or adding water to it?
 
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Old 06-11-24, 06:06 AM
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You need a valve like this or equal
https://www.supplyhouse.com/Taco-329...RoCPZoQAvD_BwE

You will also need an expansion tank and relief valve
 
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Old 06-11-24, 06:08 AM
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What is the rating of your tubing?

Assuming that your hydronic floor heat uses HE-PEX tubing:

​​​​​​​PEX tubing has a standard hydrostatic pressure rating of 160 psi at 73℉ (this is a 630 HDB rating, which applies to all PEX tubing sold in the U.S.). At 180℉, it has a pressure rating of 100 psi. However, there are different types of PEX tubing made by various manufacturers.
 
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Old 06-11-24, 04:33 PM
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A small circulator pump is needed too.
 
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Old 06-11-24, 05:06 PM
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my pipes are uponor pex pipes and 3/4 inch soldered copper m y old system was open to atmosphere (home made outdoor boiler)
This will be a closed loop using a gas hot water heater using the same circulating pump and all pipes from my old system in the house (just eliminating the pipes outside in the ground and the old stove)
I would have the new hot water tank and expansion tank and was thinking i read somewhere else that 20 psi was a running pressure for boilers so thought maybe i should run this system at that? If it is safe to stay at my house pressure (i am on a well) 30 to 50 psi then i will leave it, other wise i would change the pressure relief valve and put a regulator on the fill pipe to the desired psi

my system includes a few floor loops and a water to air heat exchanger in a furnace plenum and a home made water to water exchanger
 
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Old 06-11-24, 05:51 PM
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The boiler will have a 30psi pressure relief valve so you'll need to stay below that.
15-20psi would be fine for your system.
Typically a higher pressure is used when hot water needs to be pumped up to a 2nd or 3rd story.
 
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Old 06-11-24, 06:24 PM
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thanks everyone for your thoughts, You have all been quite helpful.
 
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Old 06-12-24, 06:37 AM
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Are you using a standard domestic hot water heater or a boiler? The former will work (and can be used at normal house pressure) but will deliver a much lower output than a boiler. Typically a water heater can provide 30-40,000 BTUh (similar to a wood stove) vs. 70-150,000+ BTUh for a boiler. The capacity you need is determined by the heat loss of your house. A radiant system will run longer (or constantly) at a lower water temperature and a boiler will provide higher but shorter bursts of heated water in response to air temperatures in a space controlled by a thermostat.
 
 

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