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Community and Q&A

Replacing Propane Boiler with Heat Pump

remodeler2000 | Posted in General Questions on
Hi all
Just moved into a house in Sonoma county and trying to get some idea of heating options as we are planning to install Solar and have the option of cheap electricity 🙂
3200 sq ft
Propane boiler/furnace (new 2 years ago) supplying the following
* Hydronic underfloor heating
* Hot Water
Dont think we need AC as the house is up on a hill and gets a nice breeze.

Wondering if it is as simple as replacing the furnace etc with a heat pump that can supply both the Hydronic underfloor heating and Hot Water system? Or maybe keep the existing system in place for backup and add minisplits?

Existing house insulation etc

We moved in 6 weeks ago. House was custom built 28 years ago. Limited opportunity to add insulation due to the design (second floor bedrooms in what would be attic space, with dormers) That said, there are some smaller loft crawl areas that are all well insulated. House also has good double pane windows everywhere.

People we purchased from seemed to spend money on a good quality build.
House has large overhangs – so seems to stay cooler in the summer. Larger bank of west facing windows – Hope it will capture heat in the winter as the sun sets, we can already feel it in the summer.
Hydronic System
7 separate zones, should mean we can only heat want we need.
Existing Boiler
Supplying domestic hot water and hydronic system is a high efficiency (and modulating) Lochinvar boiler (From what I can tell this is a higher end make) it was only installed 12 months ago at great cost by the previous owner ($30k)
Backup propane generator
Previous owner put in a Generac whole house backup generator (2 years ago) – This is useful in norcal where power sometimes is turned off during wildfire season. This also means completely removing propane from the house is not an option.
Propane usage
Based on previous occupants – They were using 1300 gallons of propane per year
Heat Pump for hot water
It’s an option but there is no space close to the existing installation and would have to be right over the other side of the house/garage. Which is the furthest from most hot water usage (Master bathroom).
Addition of mini-splits
This seems to be a good idea. Use them to limit the propane usage. Not sure how many yet. We would also get the benefit of cooling, which we dont currently have.


Welcome any advice and guidance

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  1. paul_wiedefeld | | #1

    You can add an air-to-water heat pump to cover the floors and domestic hot water. It’d excel in that climate and the low temperatures needed for in-floor heating. Unfortunately, they’re not common in the US at the moment, so finding an installer may be challenging. You could easily keep the propane boiler as backup. Surprisingly perhaps, with the state of heat pump technology, no gas boilers are truly highly efficient anymore.

    An air to water heat pump can do cooling as well, but that requires ductwork or ductless heads.

    Be very careful if you could the ductless minisplit route - multi splits (one outdoor unit to several indoor units) can turn into a huge mess quickly. One to one units are better.

  2. remodeler2000 | | #2

    I would love to do that but as you say very limited experience with air to water heat pump in the US. Options and installers seem very limited.

    1. paul_wiedefeld | | #3

      You’d be one of the first in NorCal with one that’s for certain. Air-to-air (ductless, ducted, both) will be more much familiar to contractors. If possible, duct as many rooms as you can.

    2. Expert Member
      Akos | | #4

      You might have better luck with a heat pump pool heater. With near freezing design temperature a unit with defrost should be able to carry the place. There is not much difference in heating a 300 gallon hot tub or large buffer tank in the basement. The max temperature is about right for heated slab.

      Hot water is best handled with a separate heat pump water heater or if you have excess PV capacity, a standard resistance tank is a reasonable choice.

  3. walta100 | | #5

    You may want to do the math and consider installing enough photovoltaic to run an electric resistance boiler and domestic water heater.

    This would get you off propane except for the back up generator.

    The solar with resistance heaters would have zero moving parts and should be the most reliable system.

    Given that you have fuel records you will know your heat load numbers and can size it perfectly.

    The big question is net metering and solar cost numbers.


  4. charlie_sullivan | | #6

    An air-to-water heat pump would be a great solution for you, and the right one could do your hot water as well as your floors.

    Whether it's worth pursuing that despite the difficulty in finding a contractor willing to learn it depends partly on your objectives. Do you just want an economical way to make your house comfortable, or do you want to help the green building movement, not just by making your house greener, but by helping introduce contractors to new technology that they could be beneficially applying more places?

    In any case, the first step is to estimate your heating load. One way to do that would be to monitor propane use closely this winter; you could possibly even measure water flow rate and temperature to get the actual output of the boiler not just the input.

    What is the zoning system? Seven pumps or one pump with seven zone valves? Either way, some old schemes for that consume 3X to 10X more electricity than modern, efficient options.

  5. joshdurston | | #7

    IMHO, we're still a couple years out in North America from having mainstream AirToWater Heat pumps. Many of the big players have the products globally, but not in NA, or a very limited offering. I want one, but am in a holding pattern as the NA market matures.

    So I would wait a couple years, or do an immediate Solar boost setup.
    Solar electric components are mature and fairly low cost. The challenge is working with a system designer who can integrate the solar and boiler while respecting the limits and efficiencies of both the solar and boiler.

    Lochinvar generally offers pretty good control flexibility on their boilers. You could have a electric boost mass tank/resistance boiler after the boiler, but place a boiler system temperature sensor after the electric discharge, so the boiler could compensate for any short coming. The boiler has the capability of resetting it's target SWT based on what the system temperature is doing.

    Agree that zoning with valves is the way to go. I have Grundfos delta P ECM pump serving some rads with TRVs and it never goes over 20watts, but I've seen houses with an oversized 100w circulator per zone. They could be at almost 1000watts continues before they are even turning the burner on. Old school boiler guys love to zone with pumps, they do good work with the piping but are often ignorant to the electrical repercussions.

  6. remodeler2000 | | #8

    Talked to a few companies and the AirToWater Heat Pump is not common. Going to still keep trying to see if anyone has experience.

    Best path maybe to add MiniSplits and minimize use of Propane


  7. greenright | | #9

    Keep in mind that even the best air to water heat pumps reach about 140 degree water with very modest volume. I assume this is enough for your heating load in Northern CA, but just something to consider and calculate to make sure BTUs are enough.

    1. remodeler2000 | | #10

      I wish I could find someone experienced in Air to Water heat pumps in Sonoma. At the moment I can't see it happening :-(

  8. walta100 | | #11

    Consider what you have proposed doing is very ungreen thing. Reuse Reduce Recycle! I understand you want to get off propane but really you want to junk a virtually new boiler. This piece of equipment should easily remain in service for another 25 years. Instead, you want to mine the copper and steel to build an unnecessary heat pump a total waste of resources just so you can feel good?

    Change my mind show me the math where at todays prices you can buy and install the HP+ solar for less than 15 years of propane.


  9. jayohaetchenn | | #12

    I agree with Walter A. that this is not a very "green" step, proactively replacing a nearly brand new boiler with a heat pump which is still going to use the electric grid when the sun is down (unless you have a very large ESS). I suspect you'll need a relatively PV system to fully cover heat pumps.

    If you really want to make some change, I would encourage you to put in a supplemental system that doesn't involve removing the gas boiler.

    An air-to-water heat pump is a good option, though as others noted there aren't a ton of options. The only one I know of is the Arctic (, though I have seen some air-water heat pump pool heaters lately but I don't know the brand. The installation on the other hand is very simple and any competent hydronic heating contractor can handle it; the unit is self-contained so there's no refrigerant license or knowledge required. I believe most of them produce domestic hot water too. You can literally buy it on Amazon, or if you prefer they have some reps in the US according to their website. They offer design services as well and could produce a specific plan to tie it into your existing system.

    Another option worth serious consideration in my opinion is solar hot water. The sun concentrates heat the water in an array on your roof or backyard, that water gets stored in a tank and circulates through the heating system. Such a system is probably pretty common in your area and would tie into your existing hydronics. The gas would serve as a very capable backup for the dark season. Combined with PV solar you could have a well-balanced system that gives you the (thermal) energy storage from the solar water heating, and uses the PV for everything else where electricity is needed.

  10. remodeler2000 | | #13

    Walta - '....just so you can feel good?' Thank you for the kind welcome to the forum :-)

    Getting back to the question - The goal is to be both cost and energy smart in our approach.

    Propane usage was 1,300 gallons per year at $4.11/gal that is $5,343 per year on propane.

    Best thought we currently have it to leave the current propane boiler in place but look at options to minimise usage

    Cooktop - Stop using propane - Install Induction cooktop as part of planned kitchen remodel

    Hot Water - Leave as is and continue to use. There is no close location for replacement heat pump hot water tank without getting into long runs.

    Hydronic underfloor - Leave but only use if a booster for heating is needed. Install 4 zone minisplit for heating and a little cooling on the hottest days.

    Assuming this reduces propane usage by 75% - This saves ~~$4,000 per year

    Cost of extra solar panels needed - ~$13k
    Cost of Minisplit - $20k

    Rough payback 8.5 years. This is longer than I would like and think I need to refine the figures.

    Thanks all

    1. Expert Member
      Akos | | #14

      1300 gallons of propane in your climate is a lot. There is some low hanging fruit in terms of tightening up the place that can shave a lot of that usage. Getting somebody to do a bit of blower directed air sealing would not hurt. Half story structures tend to have huge air leaks that are pretty easy to fix with a bit of elbow grease.

      The biggest savings would be to install a single larger heat pump for the main living space. With the doors open, this will tend to distribute heat to the rest of the house and you can get it in for much less than $20k. I would try for a ducted unit in the basement with simple short runs to the living space above. This would also give you the option to tie more of the rooms in if there is ever a major reno where walls are opened up.

      Most indirect water heaters are inefficient. Even when best set up, it will use a bit more gas than a power vented unit, not properly configured easily twice as much. With the high cost of propane even a resistance water tank would be cheaper to run. I would add a resistance element to the indirect if possible, if not swap it out for a resistance tank.

      Having a resistance tank in the house fed by a heat pump water heater in the garage is also a good option. This eliminates the issues of long runs and increases the overall water capacity, the BOM cost of small resistance tank and a small HPWH is about the same as a large HPWH. The operating costs would be not much more than a heat pump only option since the resistance tank would only run to make up for standby losses plus the bit of losses from the long piping. Make sure to set the resistance tank thermostat bellow the HPWH.

      1. remodeler2000 | | #16

        1300 seemed a lot to us as well. Owners were a retired couple who said they left the hydronic system on 24x7 at 68 degrees through the winter but did switch off 1-2 unused zones (spare rooms). I will take a look at leaking testing as well.

        Also wondering if the house has any real thermal mass. It's raised floor with crawlspace and timber framed. I thought hydronic underfloor worked better with a larger thermal mass to transfer heat to then slowly release? We have none of that.

        Single heat pump would be great and may have worked a couple of years ago but now we work from home more there is a need to have spaces that are further apart (either ends of the house) comfortable. A zoned system could work well.

        I was running the numbers on solar last night - We have 5.7 MWh annually to play with ie thats the max excess solar we could install and use to power heating and hot water.

        Regarding hot water - This is proving to be harder to find anyone who will touch it. Changing an already working system and adding to it is virtually impossible - esp when the design is non-standard. Thats why I was thinking of adding separate heat pump hot water tank and turning off the boiler but not making any other physical changes.

        1. jayohaetchenn | | #17

          I hadn't noticed that detail -- 1300 gallons is a LOT of propane for that climate. I feel like there must be some major leakage in your building. I am living in a 1600sqft 200-year-old building, very drafty and poorly insulated on a windy hillside in New England. Heating with propane, cordwood, and a multi-split for shoulder seasons, I use about 350 gallons and 1.5 cords, and ~750kWh (heat pump net estimated) respectively in a season. Your first and cheapest call might be an energy efficiency consultant to check for insulation and air leakage issues.

          LPG is 91,452 BTU/gal. At $4.11/gallon and using a typical 95% efficiency boiler, I believe you would be looking at $.047/kW of heat output using LPG. At 1300 gallons you are going to need to come up with 118,887,600 BTUs (34,844 kW) from one source or another for the winter.

          Say you find a 9.8 HSPF heat pump which offers an approximate COP (Coefficient of Performance) of 2.88 (equivalent watts of heat output from 1 watt of electricity) you would need more than 12 MW of electricity to produce the same amount of heat. If you produce 5.7 MWh extra over the course of a full year, you'll still need to buy another 6 MWh during the winter months. I can't speak for CA, but here in MA our rates go up in the winter (and some are even subject to higher rates at different times of day). Just to pull a number out of the air for the sake of the calculation -- $.15/kWh -- that's $900 in electricity.

          That on the surface may seem like a great deal ($900 vs. $5343), but it's theoretical and you need to consider what approach the utility company employs to compensate you for the electricity you produce in the summer but need to buy back in the winter. The efficiency of the heat pump as installed would also need to be verified. You also have to take into account the cost of installing vs. lifespan of the equipment -- I have no evidence to support it but I am dubious that my own Fujitsu heat pump if used extensively all winter every winter would still perform at peak efficiency in 10 years without some amount of major service.

          I don't want to post a referral here but I'll just say I have hired a very capable HVAC design consultant to engineer a hybrid hydronic heating system for our new house. He's never been on site and did it all remotely. He proposed a number of things that saved us money and complexity. I suspect you could hire him or someone else to provide detailed plans for modifying your own system correctly.

          1. remodeler2000 | | #18


            Recommendation for a design consultant would be great thanks

          2. jayohaetchenn | | #19

            I'm not sure if it's allowed to post referrals in the forum, but we worked with Daniel Schlicher of DS Design Consultants.

  11. Deleted | | #15


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