Adding hydronic floor heating to existing slab with no height constraint on a budget

linkss56

Hello, I've read so many things about overpouring on top of an existing slab but all of them I have read have some height limit.

What I've got is 3 separate rooms for a total of 800 sq feet. The existing slab is 4" thick with a moisture barrier under it.

I already have 1000s of feet of 1/2" pex, concrete mixer, and 3 brand new grundsfos pumps.

Im thinking I need to put down some insulation on top of the existing slab to reduce heat loss going down into the existing slab, not sure what the cheapest thing to put down is or how thick it should be and if I should put a sheet of plastic down between the existing slab and the insulation?

Then for starters just using my hot water heater at first then adding a solar tank and solar heated water to offset water heating cost or a outdoor wood boiler if nessasary down the road. What else would I need ? The finished floor can either be bare concrete that I would finish or tile on top really I could do anything the main thing is cost and I would be doing one room at a time. I have access to any equipment needed.

I've also considered a hybrid geothermal setup also so I feel hydronic is the way to go over electric because of all the options to add extra heat sources.

After reading hundreds of things where they've done it 100 different ways I'd appreciate some input on this. I live in the Midwest climate zone 5.

Thanks so much in advance and sorry if this is such a redundant topic.

GroundUp

Definitely want insulation of the XPS foam variety, 2" thickness 25+ PSI. Is the pex you have o2 barrier? Using the same WH you use for DHW is an invitiation for illness (Legionella) and I would suggest avoiding that at all costs. A separate "heat only" WH can do what you need, but may not be up to code in your area as water heaters do not have an H stamp for space heating like boilers do nor is the efficiency anything to be proud of unless electric fired. Doing this right is not going to be cheap- you can pick one or the other

linkss56

I've got lots of extra water heaters that are electric so I can separate from my dhw heater no problem. Is there any other down sides to using non o2 barrier pex? What size water heater would be the best to use for now? So 2" foam board then wire mesh on top with pex wired to it? How far should my loops be spaced? Is there anything else I would need. I'm a jack of all trades and used to be an electrician by trade until I became a disabled veteran in the Army. Do I need anything between the old slab and foam board? I live in the most lax county in the state when I moved here I called about building permits and stuff and they said I didn't need any and could build a power plant in my yard if I wanted with no permits so I don't really have any issues there. Thank you for the advice, it's greatly appreciated.

Alan (California Radiant) Forbes

Downside is that you will have to pay more for bronze or stainless steel pumps because cast iron pumps won't tolerate the oxygen.
Spacing is determined by your heatloss. The higher the heatloss, the tighter your spacing.
Slantfin has a heatloss calculator. Go there and do the calc's and then we can have a better discussion.

http://www.slantfin.com/slantfin-heat-loss-calculator/

nibs

Look for deals on insulation, you can sometimes get good insulation from a roofing tear off, I have found roof mate 4" thick in good condition at a good price.
IMO no need for mesh, just add fiber into the mixer for strength, and staple the pex directly on the foam. pressurize the pex 100 psi is usual. Use a super plasticizer to reduce water content.

HomerJSmith

If height is not a problem, then put down insulation on top of the 4" slab. If you use insulation high density, etc., then you don't need a bond breaker barrier under the over-pour. The thickness of the insulation will be dependent on what you think your backloss will be which is based upon the coldest day of the year. The thickness of the over-pour should be 1 1/2" with the pex on the insulation.

Your layout and design will also be based upon the coldest day of the year. The max length per circuit of 1/2" pex is 300'. All circuits lengths should be within 10% of each other.

If you use a DHW heater for you heat source, then plan on having two circuits, one DHW and the other heating. Separate the two circuits with a flat plate heat exchanger, so there is no intermingling of water.

If you aren't using 02 barrier Pex then use all copper, bronze, or stainless steel components in the heating section. China makes cheap array of manifolds and such out of stainless in terms of cost.

To be successful you need to know what you are doing, so see, Caleffi's Idronic series on YouTube or read the magazines.