Gas Instantaneous Water heater and Radiant floor?...BP

Boilerpro_2

Client is thinking of replacing an electric water heater used to supply heat to a small 1950s slab radiant floor (rest of house is scorched air) with a direct gas fired instantaneous unit. Wondering how well this works, what to look out for, and recommendations? Thanks all for all you do!


Boilerpro

Dana

I think you'll have temperature control problems. The instantaneous gas sytems fire by way of a flow valve and modulating gas valve. I'm not sure you could get enough flow through the unit with a circulator to even fire it. And if it fires it would probably hit temperature pretty fast and shut down. Maybe with a storage/buffer tank you could do it.

Bill Riordan_3

Flow

I agree, I've seen many installs where correctly sized circulator on the radaint loop produces G.P.M. too low to ignite burners. Trying to raise G.P.M. will cause radaint loop to perform poorly. Just my thoughts.

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Boilerpro_2

Those were my concerns too

Sounds like a small gas fired tank may be the way to go. Anything out there like the combicore, without some of the reliability problems I've heard about?

Boilerpro

Michael B

I just

saw something come over my desk from Triangle-tube. Let me see if I can find something on the web...

Michael Bleier
Able Distributors
www.abledistributors.com
"The Supplier Who Works With You"

Michael B

here is the

link to Triange tube combi units

http://www.triangletube.com/redirect/frdirwaterheater.htm

good luck,

Michael Bleier
Able Distributors

Boilerpro_2

Thanks, I'll have a look. NM

Josh M.

Hold up

I have used a Rinai instant hot with a modulating gas valve in small applications before. The problem is you can only go up to something like 7-8 GPM. The unit only needs about .5gpm to fire. If you need to increase the GPM through your radiant zone obviously you can do that on your secondary loop. I have found these units to be actually a much needed product for condos and cabins. It is great because it modulates between 19-180 btuh/hr giving it about 87 percent efficiency.

hot_rod

I've heard 6 gpm

max on the Rinnai, with the highest head pump money can buy

Also there was an issue with the burner modulating back when it started seeing warm return temperatures. The dealer here said a special "radiant application" board was in the works to correct this. Maybe it is available now.

It's the pressure drop through the HX that limits most instantanous/ radiant. Also the code approvals in some areas.

hot rod

Unknown

> I think you'll have temperature control problems.

> The instantaneous gas sytems fire by way of a

> flow valve and modulating gas valve. I'm not sure

> you could get enough flow through the unit with a

> circulator to even fire it. And if it fires it

> would probably hit temperature pretty fast and

> shut down. Maybe with a storage/buffer tank you

> could do it.



Definitely either buffer tank or make sure you get a unit specifically made for radiant. Using a lot of instantaneous water heaters for radiant will instantly void your warranty as well as damage the unit over a relatively short period of time.

As others have noted, definitely check the numbers again what you're designing for as well for GPM required, pressure loss, output, etc.

Boilerpro_2

Thanks, guys,

I haven't run a load because I haven't been back there to measure, but I can't see it being over 30,000, and likely alot less. As for code approvals, who knows. Here in Illinois there are no licensing requirements,etc. whatsover for heating contractors, so just about anything goes...prety scary!

Boilerpro