any one have experience using the new condensing waterheaters rated for radiant heat vs using mod/condensing boiler except  2000 less in building budget.  we have a heat load need of 48 to 75k btu depending on garage heat use  I plan to use plate exhanger for dhw. 

Another issue we are working with is the radiant floor heat radiating thru steel joists and concrete  acting as ceiling radiant.  our basement and main living area will have radiant floor heat and concrete ceiling with radiant in it (the floor above)  Do you think we will have issues of overheating or heat balancing.

current project Faswall ICF, speed floor suspended concrete floors with radiant.

Scott Dual
Dualpurpose Construction

Please list Condensing water heaters rated for radiant heat.

Each floor must be isolated by insulation to control temperature.

Not my post, but how do you feel about a Polaris being used in a closed system?

works, but not much cheaper and not as reliable as a good mod/con.

the Phoenix looks like a pretty good unit. Pretty hard to think that running it at 140 (safe DHW temp for storage) it's going to be as efficient as a mod/con which can go down to 80 or so in a concrete/ICF type situation pretty easily.

If you had a lot of low mass zones, that's another story, but still... even so... you are limited by DHW temp. Even 120, if you don't care about bacterial amplification, is much higher than many radiant systems need to be run at.

some that I have used for dhw but say are also rated for air handler or radiant rininia, noritz, and navien cc240, the most exspensive for any of these is 1500.00 not 2800 + for wall mount boiler. (I do not have rinnia(sp) and noritz model # right off hand been using the navien lately)

my system is designed to run at 110 to 120 so do not need higher boiler temperture

I wander if it has to do with market distrubitiion Boilers are from HVAC and Boiler trade and on-demand are marketed thru plumbing

Just curious.

I am not aware of any tankless water heaters approved by the manufacturer or local codes for heat only application. Much of my work is involved in replacing these "cheap" alternatives with purpose-built Mod/Con boilers featuring outdoor reset, warranties and factory design support.

People always ask me why their fuel bills are so high.

If your system is indeed designed for the temperatures you mention (you would have to do a proper heat load to determine this) then your unit will provide the same temperature all season that it is designed to deliver for a week or so (during the coldest week of the year). Higher fuel bills, more cycling, room temperature control problems.

Boilers and water heaters are marketed to and by plumbers primarily. Easy access and price should be the last criteria for wise purchasing, but seems to be more rare every day.

Oil as a fuel source combined with high efficiency could be a limiting factor as well.  Is there even such a beast.