DHW Heater as heat source?

[M&S]

Wondering if anyone out there has seen any information about using a standard, or high efficiency, LP domestic hot water heater as a heat source for a small radiant heating application? We have an application where a customer needs a temporary heat source for a small addition with a heat loss coming in at 28Kbtu's. There will later be a central boiler on site but the addition will need to be heated in the interim. We are thinking a 50 gal. high efficiency LP water heater, closed loop, providing no DHW (feeding the radiant only) may work. With the radiant loop containing only 7 gallons of water and most LP units coming in around 40kbtu input it may be doable but looking for input.

We are trying to avoid a small HE boiler for such a small space and a temporary setup.

Thanks, Mark

[Ned Flanders]

it works great, I have set up a few of them. I have always wanted to put wheels on an on demand hot water maker to have a portable heating system. I like a primary/secondary loop setup, but where you are temp you might be able to skip that.

[M&S]

Thanks for the reply, So by primary/secondary you mean run the DHWH at a higher temp. and pull the radiant off with a thermostatic mixing valve at a lower temp? I had considered this as an option if the DHWH only has a low limit of say

100deg. F (too hot for radiant). This would surely be the way to go if the DHWH was providing potable hot water in addition to supplying the radiant loop or perhaps to boost recovery. I am thinking where the heater will have a relatively high return water temp. the recovery will be much higher than the 40gal/first hour most call out when using city 50 degree city water.

Thanks again for the input, Mark

[Ned Flanders]

I do it also to make more efficient use of my circulator. you can use ball valves instead of a mixing valve for your temp application.