Please help a novice: need new water heater, want to add hydronic over slab

doctaiam

Hi - we're buying a house with a 50-year-old A&O PermaGlas water heater, which we're replacing. It's in the utility room off a daylight basement on a concrete slab. The rug on the slab has got to go, and the forced-air registers for the basement are in the ceiling or the top of the walls. If it doesn't cost a fortune, we want to put in a hydronic system (and a cork floating floor.) The area is about 950 square feet including a hallway, 2 bedrooms and a bathroom (currently tiled.) The climate is rainy, though winters are mild, and I am told the slab is cold underfoot all year.

I spoke to a plumber who proposes installing a standard 50 gallon Bradford White heater. I spoke to a radiant floor heating contractor who suggested a high-efficiency condensing water heater and mentioned the need for a flue. He discussed a heat-exchange system for the space-heating side of the system (which I understand has to be separate from the domestic hot-water system.) He said Warmboard+labor usually costs equal to or a little more than a site-built system+labor, but he can build a sleeper system that will be slightly thinner so we'll lose less headroom in the hall. What's advisable, please? I read that high-efficiency water-heaters are often high-maintenance as well. I need simplicity, dependability and a system I can afford: serviceable, not deluxe. Thanks in advance.

GroundUp

Firstly, I would find a new heating contractor. Water heaters are for heating water, not space heating. Sounds like you need a new water heater anyway, would a combi unit be an option? If headroom is an issue, maybe consider radiant walls or ceilings and keep the floor where it is

doctaiam

Thank you. I'm confused - it seems like the discussions on the board often talk about the pro's & con's of using a combination water heater unit for radiant hydronic, and a lot of people come down on the side of using a water heater plus a heat exchanger - because it's simpler, and if one part of the system breaks down you don't need to replace both.

We definitely do need a new water heater. So sure, a combination unit is an option. I just don't know what's wise.

But since headroom is an issue, I don't think radiant ceilings would help! And unfortunately, the corridor is kinda narrow.

hot_rod

Radiant walls may be an option?

Those over slab installations really need some insulation R value 1" or more, but that ends up eating into the headroom. Ceilings can be done with 1/2" of dry board system, same for walls.

Start with a heat load calc first to see how much heat you need to move into the space.

While controversial, conventional water heaters have been used as stand alone radiant heat source.

Adding a flat plate HX to a DHW is an option for small loads and you can size the HX exactly to the load and the tank buffers small loads nicely, probably low 80% efficiency unless you buy a condensing water heater.

Danfoss used to offer a nice packaged HX assembly, ZCP just for water heater add ons. It came with the HX, pump and control in a nice powder coated enclosure.

doctaiam

Thank you very much. If you wouldn't mind, please tell me what you see as a non-controversial radiant-heat source. I want to keep things simple.

hot rod, Sounds like you feel a unit like the Danfoss heat exchanger is a non-insane set-up. But does this whole concept mean we need to size up the new water heater? If we need 50 gal for household use, and want to suck heat out for space heating, do we need more gallons? More BTU's????

I'll figure out how to calculate the heat load. Already I figured out all the initials except "ZCP." (Zero- something-something?) Again, if you please, tell me what it means that the tank buffers the load. I am a no-kidding novice... and I appreciate you guys for offering your time and expertise.

hot_rod

Some are of the opinion that a heat source for low temperature hydronics must have a ASME "H" stamp. In some cases the inspectors may require it.

Personally I believe the heat source can be safe and efficient regardless of the ASME stamp. I know some manufacturers sell tank type hydronic heaters that are not stamped. Conventional water heaters are use in combined systems like the State Apollo. Not my favorite application mixing potable and heating water. Perhaps with a short run to a fan coil and elevated temperature operation it could be safe from legionella potential?

Check and see if they are still available and the cost, the Bradford White CombiCor is a tank with a coil inside for hydronic, they have a 65 or 75,000 BTU burner. It is one way to get DHW and hydronic from a single unit. They have conventional vent and sidewall options, at least the did.

HTP also has some tank style combo units that are condensing and high efficiency.

Really a flat plate HX and a pump can turn any water heater into a combi unit. Tee into the top and bottom of the water heater, a stainless pump to circulate thru the HX. Pipe the radiant to the other side of the HX, pump, expansion tank 30 psi safety, air purger, etc.

Yes define the heat load to be sure you have adequate BTU to cover DHW when heat is at design.

I don't think those Danfoss ZCP (zone control panels) are still available. I do recall seeing other brands, built in Canada I think. I'll try and find info.

doctaiam

Thank you!

Gordy

Have you decided on what floor coverings will be used after the renovation?

Radiant ceilings, and walls can offer great comfort. You are already insulated up there (I hope), and the build up is far less than a worth while radiant floor done correctly with proper insulation. Plus you don’t have to deal with radiant friendly floor coverings.


You deffinetly need to do a heat loss calculation FIRST. Anyone telling you they can do it this way, or that way with this heat source, or that with out a heat loss walk away.

Radiant ceilings, and walls can run a higher temperature than radiant floors. This can give you two benefits. Less tube density than a radiant floor because you may be able to run hotter SWT. This cuts down on the panel cost. Or same tube density as radiant floor this would lower water temps, and benefit a high efficiency heat source.

None of this is a known until your heat loss is performed. This dictates water temps, tube spacing, heat plant sizing.

This is a case where if someone is offering a non asme stamped appliance for heating, or dual purpose, the installer needs to be aware whether it is, or is not code compliant by the local authorities.

.

doctaiam

Thanks, this is great information. Very helpful. We're planning on cork tile. Radiant walls are not really an option due to the kind of walls. I'm still working on getting the heat-loss calc. Haven't closed escrow yet - planning ahead.

hot_rod

Thin cork I hope as it is not a great heat transfer material. They used it for freezer wall insulation years ago.

Ceilings are a fairly easy retrofit and with higher surface you may not need as much square footage And no cork up there.

I like panel radiators with TRVs, ultimate adjustability many choices