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Air-to-Water Heat Pump to Replace Boiler

ineffable | Posted in General Questions on

My 20-month-old oil boiler has failed (Buderus g115/ws3), and the labor to repair it under warranty is twice what it cost to install it new. In light of how awful my experience with the boiler has been, I am looking at other options.

Are there are air-to-water heat pumps that I could ‘drop in’? I have conventional baseboard, 1900 square foot home in central CT with a 75,000 BTU heat load on design day per my calculations. Generally, even on cold days the boiler only ran a max of 25-30% of the time.

There is no natural gas available, and I cannot run ductwork, install minisplits, or install radiant floors (house construction is unusual). Baseboard and valance heaters can be added or replaced with higher output if needed.

If such products exist, tips on installers would also be appreciated. Those I have spoken to here do not sell air-to-water units.

Thank you!

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  1. paul_wiedefeld | | #1

    Shocking for a boiler like that to only last 20 months. What happened?

    Use the fuel usage method to determine your heat loss, as your calculation of 75,000 Btu/hr actually exceeds the capacity of the G115WS/3, which you say runs only a fraction of the time on the coldest days. So I expect the true heat loss is ~30-40kBtu.

    This can be accomplished but is a bit difficult, as this is a niche product in the US currently. You'll have lower temperatures produced from an Air-to-water heat pump, so a balance needs to be found between a combination of backup heat, higher output radiation and reduced heat loss as you'll want heat load/linear feet of baseboard to be about 300btu/lnft or lower.

    Brands include SpacePak and Nordic. A great resource is Caleffi's Idronics journals, they have advice for exactly this situation.

  2. walta100 | | #2

    Did you get a second opinion?

    Did you contact the manufacture?

    In general boilers tend to have a longer service life than other types of equipment It would be interesting to know that failed and why.

    Consider photovoltaic panel, net metering and an electric boiler may not be a bad combination if you get enough sun.

    The “heat pump boilers” are almost a rare a hen’s teeth, prices as if made of gold plus well-trained technicians are rare as the market niche is so small and forget about a warehouse full of parts in your town.


  3. ineffable | | #3

    Thanks for your comments! :-)

    I keep my house at 60 so I may only need 30-40kBtu at that temperature. But not everybody is as warm-blooded as I. The house is not a paragon of efficiency, being from 1978, although the small windows of an A-frame may help reduce loss.

    Sun is a challenge due to 100+ foot tall pine trees and a mountain to the southwest.

    The seal between the boiler sections sprung a leak and creates a pool of water in the combustion chamber. It won't burn right with water in the chamber. Basically a manufacturing defect.

    Buderus will replace the block only for a $200 processing fee, but installation of the block is estimated to take 4 days and cost $6000. This is on a boiler that cost $1600 new (plus about $1000 in parts); I have already spent $1100 diagnosing the problem plus was required to spend another $500 to have a tech come out and wait for Buderus to call to repeat what he had already found.

    I'll pull my oil bills and see how much fuel I have burnt.

    1. paul_wiedefeld | | #8

      20 months ago is very different from today’s prices. $6k just might be the market rate now.

  4. nynick | | #4

    I know propane is considered expensive, but Combination Instantaneous Boilers might do the trick for you. They're efficient and dependable.

    In central CT, wood is also easily available. A wood stove might help cut the cost of the propane.

    I would also take another hard look at minisplits. They can go almost anywhere and would eliminate your baseboards and provide AC to boot.

  5. ineffable | | #5

    Thanks, Nick. I may be able to get a new propane boiler for free.

    Minisplits won't work because my house is an A-frame (actually two) and structural post-and-beam so there are no wall spaces that work. Also I can't breathe in forced air or A/C. (But if I do a hydronic heat pump I could get A/C of sorts ... Sigma makes valance heaters with condensate drains.)

    1. paul_wiedefeld | | #6

      There's often a misconception about radiant heat being "radiant": mostly it's convection and baseboards are a prime example of this. They function nearly the same as a furnace/ductless minisplit minus the blower (some even include the blower) and they don't have the filtering capability of a forced air system.

      A combination propane boiler cannot be expected to be more reliable than a standard efficiency oil boiler like you already have (excluding this one manufacturer defect).

  6. nynick | | #7

    Paul is right, but I didn't think you were considering another oil fired boiler. That's the easiest thing to do.

  7. walta100 | | #9

    Can we assume they have tried a few different brands of stop leak additive?

    Can you document a service call for the leak before the labor warranty had expired?


  8. ineffable | | #10

    I haven't tried stop leak, anything I could.

    I reviewed the Buderus warranty. They do not cover labor under any conditions, even in the first year.

    I don't know what the purpose of a warranty is when repair under warranty costs about twice as much as a new installation did.

    1. Expert Member
      NICK KEENAN | | #12

      The warranty is a sales and marketing tool for the manufacturer. Some manufacturers value their long-term reputation and honor their warranty obligations, and some don't. I'm sorry to hear about your experience with Buderus, I had thought they were a reputable company but I guess I was wrong.

  9. walta100 | | #11

    Seems to me most reputable contractors do cover labor for some amount of time and list that fact proudly in their bid.

    Seems to me if you can show there were repair attempts for the leaking problems happened before the labor warranty had expired, they could be convinced to repair the unit at no cost.

    I am not suggesting you add stop leak I am suggesting a professional would have tried a few before recommending a system replacement.

    Seems to me before you drain your wallet a second opinion would be money well spent.

    I understand the people on the forum are very knowledgeable about boilers.


    1. Expert Member
      NICK KEENAN | | #13

      Usually if contractors offer a warranty it's relying on the manufacturer's warranty. If the manufacturer is stiffing the customer it's probably stiffing the contractors too. If that's the case the contractor probably wants nothing to do with the service because it's a no-win situation for him.

      I interpret the $6000 price tag as a signal that the manufacturer isn't going to honor the warranty and the contractor wants nothing to do with the whole situation. Even the $200 "processing fee" is ridiculous. This is a boiler where the installed cost was $1200 and the manufacturer wants $200 to replace a part under warranty? The manufacturer's cost for the entire unit can't be much more than that.

    2. user-6623302 | | #15

      Yes, do this. Maybe you just have a bad contractor and replacement is not necessary.

  10. gusfhb | | #14

    Wow, just saw this
    I have had Buderus boilers for 18 years, I am really surprised that they are treating you this way.
    It really has lawsuit written all over it.
    I would pop over to to see what those guys have to say.
    This, IMHO should have been replaced at now cost to you one way or another

  11. user-6623302 | | #16

    How about a Youtube video about how these boilers are crap and the warrantee is worthless. Might get their attention. Let the folks over on heating know the story.

  12. Jud_Aley | | #17

    You should definitely post this problem at heating

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