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Community and Q&A

Leaking indirect water heater and inefficient AC

ranson | Posted in General Questions on

I’m buying a house near Worcester, MA, (zone 5). The house has two floors and a walkout basement. It has leased solar. It’s heated by an oil boiler with an indirect water heater. The boiler and water heater are from 2015, but the water heater was installed with some slight leaks and has corroded to the point of needing replacement.  Additionally, the house has an AC system in a conditioned attic. The AC is a 10 SEER Goodman unit from 2018.

I’m trying to come up with a 5-year strategy for HVAC improvements. I would like to stop burning oil. I’m also planning on insulating the basement, which will mean moving the existing radiators. I have a bunch of different potential plans.

1. Do nothing but repair what’s already there. Replace the indirect tank with a like unit. Replace the basement radiators with like.

2. Prepare for an air-to-water heat pump. In the short term, replace the indirect tank with one that is compatible with a heat pump. Longer term, replace the boiler with an air source heat pump, and replace/retrofit the attic unit with a ducted hydronic coil. Use the radiators for primary heat. Use the attic unit for cooling and backup heat. Install a fan coil in the basement for heating and conditioning.
2a. As above but convert the attic unit to an air source heat pump for backup heat.

3. Prepare to move away from hydronic heat. Replace the indirect tank with a heat pump water heater. 
3a. Eventually: Install a new ducted air-source heat pump to heat and condition the first floor and basement. Replace the attic unit with an air-source heat pump to heat and condition the upstairs.
3b. Eventually: Use minisplits everywhere to heat and condition the house.
3c. Eventually: Use minisplits on the 1st floor and basement, but replace the attic unit with an air-source heat pump.

What should I take into consideration when planning this out? Am I missing better ideas?

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  1. Expert Member
    Akos | | #1

    The indirect needs to go no matter which route you take. Most air to water heat pumps can't make water hot enough so you need a resistance tank in series to boost it. When you look at the cost of materials and actual COP it makes no financial sense.

    Replace the leaking indirect with a HPWH now and enjoy the cost savings. Most likely the savings in oil usage will pay for the HPWH in a couple of years.

    Air to water is still in its infancy in north America. Unless you DIY it, I doubt it can be made to work. Your best bet is to replace the rads and go for plan 3a. I would make one change and only replace that attic AC when it dies. In the mean time the bedrooms can be heated during the day by the air handler in the main floor if you leave the doors open and during the night by a couple of plug in panel heaters or baseboards.

  2. paul_wiedefeld | | #2

    If I’m understanding correctly, the existing AC isn’t ducted for the first floor, just the second?

    Air to water would be the ideal solution, but it’s extremely niche still. You’ll probably receive significant contractor pushback for installing a plain old heat pump, so bump that up more for air to water. 3a will likely be the easiest, but it involves abandoning the radiant system.

    An easy first step is to track how much oil you burn this winter. You’ll be told that heat pumps don’t have enough capacity so having those receipts can go a long way.

    No particular reason to keep an indirect - it’ll be expensive to heat with oil and a HPWH will be about as efficient as a air to water heat pump. There’s a reason most Americans don’t use indirects.

  3. DC_Contrarian_ | | #3

    Definitely go with the heat pump water heater.

    I'm less quick to ditch the existing heating system. Does it keep the house comfortable? I think you should at least do a thought experiment. Read this article on how to calculate your house's heating load:

    Since you're going to insulate the basement you have to estimate how much fuel that's going to save you and adjust the calculation. Alternately, you could do the basement insulation and wait until you have a year's worth of fuel bills.

    Next step is to see if your existing radiators can do the job. You need to figure out their BTU ratings when they are derated for the water temperature you'll see with heat pumps, which is typically about 125F. Compare that total with the total heating load you got from the heat bill. If the existing radiators are sufficient, you're good. If not, all is not lost. You can replace the existing AC with a heat pump that does heating and cooling and pick up some heating capacity there. You know the capacity of the existing AC. Does it keep you comfortable?

    1. DC_Contrarian_ | | #4

      I recently installed a Chiltrix CX-34 in my house in DC. I'm waiting for a little more experience before reviewing it for GBA but so far I've been impressed. It was just under $5k for a 24,000 BTU unit. Which isn't too bad if you can get away with one unit but quickly gets unreasonable if you need multiple units. I would say DIY installation is possible but is an advanced project. If it pencils out to keep your existing radiators then I would say this is a viable alternative.

  4. ranson | | #5

    I've closed on the house and have had some time to look it over and plan. Things of note:

    a. The plumbing in the house, including hydronic, is a combination of poorly done and corroding.

    b. The basement could be legally finished if it didn't have the hydronic pipes overhead and obstacles along the walls.

    c. There's very minor water damage to the main electrical panel because of item a. The electrical panel is 100a.

    d. The wiring in the house is mediocre.

    e. At least the second floor bath needs to be gutted due to poor workmanship on the shower. The first floor bathroom is a small dated half bath below it. Neither have fully functioning toilets.

    f. A portion of the basement was finished without any thought about moisture management.

    g. The attic air handler has ducts to the 1st floor.

    So here's my plan, in rough order.

    1. Measure the static pressure across the air handler in the attic. Look up the specs on the air handler, and figure out the flow it's operating at.

    2. Given the above info, replace the air handler and AC with a modulating heat pump that will work the existing ducts.

    3. Rip out all plumbing in the house, including hydronic and the water heater. Gut the basement and bathrooms. Remove the boiler and oil tank.

    4. Rough plumb the house.

    5. Replace the electrical service with 200A, rough wire the bathrooms, and add a 2nd floor subpanel.

    6. Insulate the basement with rigid rigid foam, and install drywall and a floating floor. Insulate the bathrooms.

    7. Finish the bathrooms.

    8. Finish the basement plumbing including a heat pump water heater.

    9. Install a mini split in the basement close enough to the slop sink for a condensate line.

    Is this sensible? It hinges on the attic ductwork being adequate

    1. paul_wiedefeld | | #6

      The airflow needed depends on the heat loss, so you’ll need that first. Use the oil receipts if you can. A heat pump can work even if the airflow is too low because you have the option of supplementing with electric resistance heat for the coldest days.

    2. Expert Member

      That sounds like $100K worth of renovations! If you're already rolling up your sleeves to gut the plumbing and electrical, I wouldn't let the existing ducts be a determining factor here. Rip those out too if needed, and go the way you want.

      In for a penny, in for a pound.

  5. walta100 | | #7

    Seems to me before you start buying equipment you need to do the unglamorous work of sealing up the air that is almost certainly leaking uncontrollably out of your old house.

    Once your house is tight enough to keep warm air inside. Only then should you think about buying insulation to keep the heat from radiating thru the walls.

    Only when the existing equipment has failed to the point that repair is a poor option does upgrading make economic sense. The water heater sound like it is ready for an upgrade.

    Has the Mass saves program worked on this house? If so they may have gotten the low hanging upgrades.


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