Radiant Boiler vs Hot Water Heater

Chip_2

Loking for your thoughts: Should I be looking into a Boiler or Hot Water Heater to heat the radiant system? Any preference to brands?

Backround:
I'm in the process of constructing a 2 story out-building, with a footprint of 12' X 24'. The 1st floor will be used as a shop, 2nd floor as an office.
1st floor radiant piping (1/2", Zurn PEX, 250')will be laid in the poured concrete floor.
2nd floor radiant piping (1/2", Zurn PEX, 250')will be attached to the underside of the floor, using reflective plates.
Fuel will most likely be propane and thinking of using a Tekmar256 outdoor air reset controller.

Loads:
The load calc (by Zurn), says total room loads are 8,510 Btuh and boiler output should be 10,366 Btuh.

hr

That's a fairly

small load. I have, and probably will continue to use water heaters in certain low load applications.

Keep a couple things in mind. Code issues in your area. not all code officials allow water heaters used this way.

Manufactures warranty. There may not be any Seems most water heaters are not listed to be used in closed loop heating applications, and doing so will void any warranty.

Efficiencies claims, for basic tank style WH's, range from 45-75%, depending on who you believe

That being said, I'd bet 10 of thousands of water heaters as used a raduiant heat sources. Wish the WH manufactures would step to the plate and decide on a listing to cover this application

Of course price drives a lot of WH decisions!

I'm dying to try a T-50 Munchkin for this exact application. It would give you the dual temperature ability, modulating, and high efficiency. It loves those operating temperatures. Although they are a bit more than $200, which buys a WH

I've used a bunch of Polaris WH's. The 50 gallon tank capacity handles the oversized BTU output fairly well, when controlled. Still not listed for closed loop applications, even though many contractors and online radiant companies sell them for this purpose, in both open and closed loop applications.

You can find some small output copper and cast boilers, but even the smallest would be twice the output you need at design day, and quite a bit oversized on mild weather days.

How's that for a confusing answer.

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Chip_2

Boiler vs Hot Water Heater

Thanks so much for your response!
Ok, I'm sold on the idea of using a water heater rather than a boiler. Simpler, cheaper. Took a look at the Polaris @ www.americanwaterheater.com.

Couple of things.

The Polaris is said to be a combination heater. I'm assuming domestic and radiant. I will not be using for domestic - still a good choice?

How do you pick the right size for a water heater? With a boiler, I think I would have chosen based on Btuh output. Not same with a WH?

Would like to use an outdoor reset controller (the Tekmar 256 looks like the right one). What are your thoughts using one of those guys with a WH?

hr

Remember

The Polaris is not an inexpensive water heater.Probably close in price to a small condensing boiler. You might still price the Munchkin.

Polaris shows the combo systems because the unit is not listed to be used as a closed loop heating devise.

Most, but not all of my Polaris installs use the 50 gal tank to supply the DHW. Then I use a small flat plate HX to isolate and supply the radiant. Now you are getting even more expensive for the hx and stainless pump to drive it

This gives you a high efficiency hot water heater, and your radiant, from the same appliance.

Polaris and other condensing tanks usually start at 100,000 inputs. While it may be large for your load, the 50 gallon capacity acts as a buffer and eliminates short cycles.

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