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When do Indirect water heater's pencil out?

nickh1nickh1 Posts: 16Member
I have an old house with a natural gas forced air furnace/ground source geo combo.

I added a garage last fall with an mudroom/porch to attach it to the house. I installed radiant pump at the time, but not a heat source. I recently put an HTP boiler in my shop and am happy with it, so I'm probably going to hang one in the garage as well. Heating off the existing furnace is not feasible due to layout.

One option I cam up with was to put the boiler in the basement and install an indirect water heater. On one hand, my current tank water heat has a date of 1994 on it, so I'm sure I'm running on borrowed time. But I looked at my natural gas bill's and the gas only portion of the bill, (exluding the fixed customer charge) ranges from $5-12 in the non heating months (we have a gas stove as well).

So let's say I use $200 of ng to heat my water. If I raise my efficency from .6 to .9 I'm only saving $70 per year. I would also have to assume that $10-20 of that would go to pumping cost. So if I save $60 per year and it cost me an additional $1000 to install, it takes 16 years to break even. Not to mention I have another $300 in materials to get the hot water out to the garage.

I think I'll hang the boiler in the garage and see how long my 22 year old rheem will run. Now to get rid of that condensate water....


  • BobCBobC Posts: 4,956Member
    It's very hard to beat a gas fired tank hot water heater if you have modest hot water needs. When I installed my boiler a few years ago I looked into it and it just didn't make sense.

    Smith G8-3 with EZ Gas @ 90,000 BTU, Single pipe steam
    Vaporstat with a 12oz cut-out and 4oz cut-in
    3PSI gauge
  • HenryHenry Posts: 888Member
    HTP S/S indirect will be around when your children won't be around. I installed this summer a HTP condensing PH55-100. My first two gas bills showed that I paid more for the meter than the gas consumed. You cannot look at just the efficiency rating but the system efficiency specifically the benefits of modulation. My gas bills were 47% lower than the previous two years just of the new tank. BTW we cook and BBQ with natural gas and our habits have not changed.
  • nickh1nickh1 Posts: 16Member
    Maybe I'm looking at this backwards. Perhaps, instead of justifying an oversized boiler by also heating water with it, I should justify an oversized water heater (phoenix) with a heat exchanger to heat the radiant load. My first look says that is cheaper.
  • EBEBRATT-EdEBEBRATT-Ed Posts: 5,727Member
    No need to oversize the boiler to heat DHW. Just do DHW priority
  • njtommynjtommy Posts: 1,102Member
    edited December 2016
    Some times if not about ROI. It's about comfort, and what makes the most sense for your heating needs. Sure it's hard to say I'm going to spend a lot of money with almost no return. I would honestly take an indirect over any other style of water heating.
  • nickh1nickh1 Posts: 16Member
    I wasn't oversizing the boiler on purpose, more a matter of availabilty. My heat load depending on realistically how warm I keep the garage is around 30k btuh on the high end. The UTF-80 modulates down, but is still kind of overkill for the load. Add in the fact that the mudroom which I'm more concerned about is only 9k btuh, The unit would be short cycling to death most days unlesss I run both rooms together.
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