Condensing gas tank water heaters?

[Wayne Whitney]

Hello,

Has anyone used a 90%+ efficient gas tank water heater (a condensing unit)? E.g. the Polaris line by American Water Heater Company, . Know of any others?

Thanks, Wayne

[HeatMan]

I didn't click on the link, but that looks like the one I installed for my FIL about 10 years ago. Okay unit, first ignitor lasted 6 years, now it eats one every 2 years. Even the one that I special ordered from the factory at 2X the price of the exact one from the local supplier.

Are you just going to be using it for domestic how water production?

[Wayne Whitney]

Well, I need to replace my gas furnace and gas water heater. I had been looking at a 45K BTU/hr input condensing furnace and a 150K-199K BTU/hr input tankless water heater.

So one option would be to get a 34 gallon 150K BTU/hr input Polaris condensing water heater and use an air-water heat exchanger on a potable hot water circuit for the forced hot air. I assume this would be more efficient, because the tankless water heaters aren't condensing units? It would also provide the option to use radiant floor heat in parts of the house I'm remodeling.

Does a condensing storage water heater have any trouble condensing the exhaust gases, if the storage water is kept at 140 or 160 degrees F? I guess I don't know what temperature a air/water heat exchanger circuit typically requires. Or does the condensing storage water heater only fire when water is being demanded and use the incoming cold water to help condense the exhaust gases?

Cheers, Wayne

P.S. As a general rule, is it OK to drain the condensate into a sump with a pump to a backyard drywell?