2 domestic HW htrs to be replaced by 1 indirect or direct vent?

Ed Palm

I am considering purchasing one indirect domestic HW heater to replace two gas units, what do you think?

I would heat with hot water coming from an additional zone that I would put on my Burnham RV7 Direct Vent gas boiler used for heat, which is just barely able to maintain heat in the house on the coldest days here in Brooklyn, USA. I have two seven year old, gas, 50 gal(40.9 gal/hr recovery) domestic HW heaters for my 2 unit house, one of which is always sufficient for one unit, the other is not, on occasion, for my larger portion of the house with a family of 4. Each unit has a front loader washing machine.

My other option is to purchase a single separate Direct Vent HW heater, which I actually already have all the separate external venting set up for. I'm wondering if a separate Direct Vent HW heater would be more efficient than an indirect coming off the boiler, since the RV7 for heat is so much larger a unit to heat up than a separate HW heater? When heat in the house is not being produced (such as in the summer), wouldn't an indirect be much less efficient than a separate direct vent domestic HW heater? Or, is the efficiency of those closed tanks in an indirect system enough to make it more efficient over the course of a years usage, particularly due to the boiler being in use in the winter?

Final question: what should the new units capacity be considering the usage?

Thanks very much for your thoughts

Al Letellier_9

indirect vs. direct vent

An indirect is much more efficient than a regular water heater and will last a lot longer and deliver a lot more hot water....but.....if your boiler is just able to keep the house warm at design temps, how will it ever make any hot water when its cold outside. True, most of the time it will be OK, but. I'd have a pro look at your system to determine the best options. Too many variables to make that kind of a decision with this little info.

Ed Palm

indirect would have a 'priority' valve on the boiler

My sense is that the efficiency is so high on the indirects that on the coldest days in the house, they wouldn't be draining so much heat from the boiler trying to heat the house that it would be noticed, even if it was struggling to keep the place warm. Also, if they're given a priority valve setup, they would get the heat first, so hot water shouldn't be an issue.

I realize an indirect coming off a boiler is much more efficient than standard HW heaters, but is it also much more than a direct vent? I would think which one is more efficient would change greatly depending on whether it's the heating season or not?

Al, thanks very much for having read and responded to my issue.

Larry Weingarten

Direct vent...

... heaters are not much different efficiency-wise from conventional atmospheric heaters. Check the energy factor (EF) ratings. An indirect will be far more efficient if your boiler is a condensing model.

Yours, Larry

Ed Palm

Thanks Larry, I'll check EF ratings

OK, I'll look at the EF ratings and see how the indirects compare with the direct vent heaters. My "boiler" is actually a Hot Water "boiler", so I guess since that's what's in place, I'll look very closely at the indirect units available.

Thanks for your help, Larry.
Ed