Hydronic Heat Equipment Question

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Hello everyone!

I live in a raised ranch in Northern Illinois. I recently had to replace the concrete slab in my lower level and when doing so, I installed 2 loops of 1/2” PEX-C in the slab to act as a secondary heat source.

There is forced air heat, but with the thermostat being upstairs the 2nd floor is comfortable but lower level will be cooler. I figured radiant floor heat would be a nice luxury and help keep both floors comfortable.

I’m starting to do my research and designing for how I want to get this stuff operational for next winter.

I’m limited on space to add a separate hot water heater in the utility closet due to the furnace and 40 gallon NG HWH taking up the majority of the real estate.

I am also thinking that I want to stay away from my hydronic heat water and potable water being in the same system (open loop I believe is the term?). Stagnant water seems like a bad idea to me.

In a perfect world I would like to be able to use my current HWH to heat the floor using a plate heat exchanger or something similar.

What I don’t know is if the HWH can be set low enough to not be scalding but be warm enough to heat the slab effectively through the loss through the exchanger and anything else.

Does anyone have any suggestions or advice?

Another option I am considering is finding an engineering firm to draft up a plan for the system. The money spent on a proper design will be offset by the savings of a DIY install and probably cheaper than just picking components and hoping they work. Can anyone suggest a company that I should look at? I know some suppliers online will design a tubing layout if I buy the tubing from them, but I’m past that point.

Thanks in advance!
 
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Sorry for the late reply, I didn’t turn on notifications.

I wrote down the exact number at home, but it’s in the ballpark of 500’ total
 

Fitter30

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500' 1/2" pex is 15k btu's. 40 gallon water heater 34k btu's. Couple problems using a tank water heater there's no way to run the heating system and have dhw a priority. Heat exchanger would work with injection or three way valve to keep loop temp down. Combi boiler / water heater wouldn't work because the btu's needed for dhw would make the heating side way oversize. Possible small boiler for heat and a condensing water heater would fit. Also have to look at the size of the has line.
 

jadnashua

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You're over the maximum recommended length of a loop of pex for hydronic, so depending on how it is run, you may not get as even a heat as you desire. The other thing on how even it would be is how far apart the loops are. But, it is what it is.

Did you install any insulation underneath the slab or a moisture barrier? That can affect the efficiency and comfort of the installation.

It can take days to initially warm the high mass of the slab, and hydronic in a thick slab doesn't respond well to the use of setbacks with the thermal mass. You want the slab to be fully cured before applying heat to it, and then, crank it up slowly.

With the use of a mixing valve, you should be able to temper the output going into the slab to whatever value you need. Mix the return water into the hot from the heat source to temper it.

And, yes, you really don't want to be pushing potable water into the hydronic heating loops, so a heat exchanger is a good idea if you're planning on using a water heater. Most WH aren't designed for the duty cycle a hydronic system may call for, though.
 

Fitter30

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You're over the maximum recommended length of a loop of pex for hydronic, so depending on how it is run, you may not get as even a heat as you desire. The other thing on how even it would be is how far apart the loops are. But, it is what it is.

Did you install any insulation underneath the slab or a moisture barrier? That can affect the efficiency and comfort of the installation.

It can take days to initially warm the high mass of the slab, and hydronic in a thick slab doesn't respond well to the use of setbacks with the thermal mass. You want the slab to be fully cured before applying heat to it, and then, crank it up slowly.

With the use of a mixing valve, you should be able to temper the output going into the slab to whatever value you need. Mix the return water into the hot from the heat source to temper it.

And, yes, you really don't want to be pushing potable water into the hydronic heating loops, so a heat exchanger is a good idea if you're planning on using a water heater. Most WH aren't designed for the duty cycle a hydronic system may call for, though.
He has two loops total 500' #3 post
 

jadnashua

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Yes, but I've been told 200' max loops is preferable with 1/2" PEX.
 
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I thought it was over 300’ was max loop for 1/2” pex. At any rate, I have 2”xps foam and 10mil poly. Tube spacing is 12” and remesh was pulled up when concrete was poured to get tubing near center of 4” slab.

Thanks everyone for the replies so far.
 

John Gayewski

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Your water heater isn't good enough to do both. Get a small boiler then you can use the heat exchanger to heat your domestic water. There's actually many ways you could do this, but just buying a small wall hung anything will likely be the easiest just find a different spot for it or add a closet.
 
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