DIY hydronic heating with a domestic water heater

This setup in our barn combines one water heater for hand-washing/dishes/kitchen use and also hydronic heating for the slab in this small, well-insulated room.

A small circulation pump drives hot water through about 100' of PEX in a serpentine loop that we placed before pouring the slab. There's a 3" layer of spray foam beneath the slab to isolate it from the ground and so far it seems to work nicely.

Because this setup is seasonal it is configured to be easy to purge the slab loop with compressed air in the spring so that we can continue to use the (outrageously oversized) water heater for domestic hot water without breeding bacteria in the stagnant loop.

[johnmeye]

VERY helpful---love your simplicity! It's all good....

[bimibericaMEP]

Awesome!!
If the HW system is heat pump sourced it's even cheaper to run.
I wonder if a retrofit solution could work with a PEX HW COIL in an exchange chamber with a fan to circulate the warmed air through a duct system. The recirculating pump would not be necessary.

[paulquesnel]

Interesting...We just equipped our new home with all propane appliances and heating system in 2016, however Canada's Liberals have now declared war on fossil fuels even though we are at 1.5% of world carbon emissions. My bad, getting side tracked. We are considering tapping into our in floor on demand boiler circuit with an Electric HWT to save on the now ridiculous cost of propane. Have your hydro bills gone up a lot using the electric tank ?

[portlandlocalchurch]

That is pretty much exactly what I plan on doing in my garage, I have a newly poured slab with pex in it and insulation foam board isolating it. Now i need a pump and valve install to warm it up..

Hows your little system working so far?

[joedean]

how efficient is this? What were you using? How many sqft? Electricity saving vs fuel?

[teejay]

Isn't it dangerous to mix your domestic hot water with hydronic system water? I thought that could lead to Legionnaires Disease or something?

[fenderbender]

genius 230 degrees circulator temp btw

[jeromewelch]

Did I hear you correctly? This is a dual use or purpose installation, domestic hot water and radiant loop heating? That's never a good idea! What's with the T&P connected to the gray water system? That's a potential cross connection. I don't see any pressure control in your design anywhere? These two systems appear to be operating at the same pressure? If you want to do this, I highly suggest you use heat exchanger allows for loop Isolation…. Peace.

[richardsayers]

scary, you should never let the hydronic heating water mix in the same tank that gives you domestic hot water, the bacteria could be bad, if you start getting sick for no reason think of that. easiest fix is to have two tanks.