Month: April 2021

All solar installers I have ever met install enough solar to offset the current electricity usage. Adding heat pumps will increase the electricity usage and decrease the heating fuel usage. Hence the ROI on a heat pump is going to be based on the cost of the additional electricity needed to run the heat pump not the current cost of electricity (whether from solar panels or just from the utility). Installing heat pumps powered by utility electricity at 23c/kWh will be about breakeven in terms of heating costs vs heating oil and will be more expensive than heating with natural gas. I think you said you were on propane, it will definitely be cheaper than propane, even if you have to use utility electricity. By far the best way to do it is to install more solar panels at the same time as the heat pump. If you don’t have the roof space to do this, the next best option is to get community sourced solar which is 100% solar at about a 12% discount to utility rates or about 20c/kWh. With a mini-split heat pump at COP (efficiency) 2.5 the heat in your house is going to cost you about 8c/kWh or about the same as heating oil. Propane is more like 11c/kWh of heat in your house. With a ducted system the COP is likely to be more like 3.0 and heat in your house would cost under 7c/kWh which is cheaper than heating oil but still more expensive than natural gas (which is about 5c/kWh of heat in the house). And remember, you have to buy the heat pump whereas you already have the furnace. This is why the most cost effective way to add a heat pump is when you need to replace your AC unit. Finance the new heat pump with the 0% interest Heat Loan and the cost difference between replacing two AC units and upgrading to two heat pumps is only about $3,000. 

A paper published in Nature Energy in October 2020* states that houses with air-sourced heat pumps sell for between 4% and 7% more than comparable houses without heat pumps. This research was done on 450,000 houses across 23 states in the USA. For many houses this premium exceeds the cost of adding a heat pump.

If you are looking for a house with heat pumps this research suggests you should do the opposite and look for a house without heat pumps and add one yourself because the house price premium exceeds the installed cost. This is true if you are paying the full cost of the heat pump, not just the incremental cost of the heat pump compared to replacing the AC unit. 

The authors put this seemingly  irrational behavior down to people not understanding heat pumps, plus the hassle of searching for one and installing it. 

This work on house price increases caused by reducing utility bills by using heat pumps is 100% consistent with prior work showing the house price increases by $20 for every $1 cut in utility bills. 20:1 implies a discount rate of 5% is being applied to the additional cash flow generated by the lower utility bills. 5% was the after-tax mortgage interest rate when these studies were done in the 1990s. The 4-7% house price increase observed with heat pump adoption implies an after-tax mortgage interest rate of 2.4% – almost exactly what it was in 2016 to 2018 when these heat pump studies were done. It turns out consumers are extremely rational when it comes to paying higher house prices in return for lower utility bills, whether the lower bills come from solar panels, heat pumps or just insulation. 

*Estimation of Change in House Sales Prices in the United States After Heat Pump Adoption. Nature Energy October 2020, Shen et al.

Q: What about installing the heat pump in a greenhouse? Maybe removable for the summer.

A: I have not done this in a greenhouse, but I think it is a good idea. Effectively I have done something similar by bringing plants indoors in the fall and keeping them in our sunroom. The sunroom receives a very small amount of heat from our house heat pumps because it is at the end of the ductwork and has no return vent. But, using LED grow lights (powered by my solar panels) I was able to get red ripe peppers at Christmas. They tasted great!

I tried to ask this tonight, but in addition to the hot water radiator situation, for Heat Pump Hot Water Heating (for your potable hot water), what temperature can those heat pumps keep your water at? If it can’t keep it above 120 continously, that would be a huge health hazard: “Water conditions that tend to promote the growth of Legionella include: temperatures between 20° and 50°C (68° – 122°F) (The optimal growth range is 35° – 46°C [95° – 115°F])” from OSHA

A: My HPHWT keeps the water at 140F which is hot enough to kill bugs. This is hot enough to scald skin so the 140F water is mixed with cold water at the valve to bring it down to a safe 125F. I have had no problems with this.

A: Yes. The output air temperature of my Bosch units of over 100°F. Also, that chilling effect of feeling even warm air rushing past your skin is less prevalent with modern heat pumps because they operate at much lower fan speeds (but almost continuously) rather than the on/off of the older fans. This makes the new fans much more energy efficient as well as making the heating system more comfortable.

A: Heat-pump hot-water heaters are about 400% efficient or more than 4x as efficient as even the best natural gas furnace.  They are even more efficient than air-sourced heat pumps for heating your house. This is because they take the heat from the air in your basement which is probably at 50°F all year round. Air sourced heat pumps for heating your house take the heat from the ouside air and, in winter that could be at 10F. All heat pumps get less efficient as the temperature drops. Our basement cooled by about 8°F after we installed the heat-pump hot-water tank. But this included the effect of insulating the hot-water pipes and insulating the ductwork in the basement, so the effect of the heat-pump hot-water tank alone was less than 8°F. I am  guessing that it would be 2-3°F on its own. The way to avoid this cooling of the basement cooling the ground floor is to add insulation to the ceiling of the basement. I added 12” of fiberglass making it about R38.

I am guessing that you are heating with natural gas and currently have either a direct-water heater (which means it has its own burner separate from the furnace) or an indirect-water heater (which means it is heated from your furnace and is essentially just a heating zone on your heating system). I would suggest you look at a heat-pump hot-water tank. These are very cheap to run. Ours provides all our hot water for under $300 a year whereas our old oil-fired indirect water heater cost us over $500 a year. And that is with us paying 23c/kWh for electricity. If you live in Wellesley (just a guess from your email address) you are paying half that from the MLP, so your cost would be $150 a year. A heat-pump hot-water tank will also dehumidify your basement which is a big advantage because basements always get damp either from condensation, water leaks or rising damp. Because it takes the heat from the air in the basement, your basement will get a bit cooler, ours cooled by a few degrees F. Because of this it is better to also insulate the ceiling of the basement so that the heat from your house does not go down to your, now cooler, basement. This is very easily done by just pushing fiberglass batts in between the rafters on the ceiling of the basement. I did this and it cost me $1,000 in insulation and I installed it myself. It is saving us around $3,000  year. If you do this wear gloves, eye protection and a face mask (like your covid one) because fiberglass fibers can irritate. It is completely safe once you have installed it. 
Heat pump hot water tanks can be bought from Home Depot or Lowe’s for about $2,000 and installation will probably cost you $250 each for a plumber and an electrician. Alternatively your plumber can buy it for you and install it. We bought ours from State/AO Smith (they are the same company) but there are many other manufacturers. Ours paid for itself in about 10 years on the energy bill savings. An indirect tank will cost you about $1,500 and will have no savings from your current bill. I have no experience with a tankless gas-fired hot-water heater but I am guessing that they would cost about the same as an indirect tank and are probably slightly cheaper to run than your current tank. However you get no bill savings and no dehumidification, both of which are significant benefits to me. 

A: Yes, if you do not have ductwork for AC. If you have the ductwork for AC then the best solution is to connect your heat pump to that duct work. It will then both heat and cool via forced-air circulation, so your primary heating will now be by forced-hot air not forced-hot water. Not everyone likes forced-hot air heating, though I prefer it to forced-hot water because it creates better air circulation. If you do not have ductwork, you can add heat pumps that heat the water for circulating in the radiators. Please see the answer above.

Another alternative to adding ductwork is to install mini-split heat pumps rather than a ducted system. This is what we have at our rental property. Having experience with both ducted and ductless systems I prefer ducted systems. The air circulation is better, the installation cost is lower (if you have the ductwork in place) and the efficiency (COP) is higher, in our case the COP on our ducted system is about 3.0 and on our ductless system is about 2.5.

There are also hybrid solutions where you put new ductwork in the places that are accessible. Usually the first floor is accessible from the basement and so it is fairly cost effective to add ductwork to the first floor from below. Likewise it can also be cost effective to add ductwork through the attic to provide heating/cooling to the top floor. If you do add a heat pump to the attic the attic needs to be well insulated and the heat pump needs to be inside that thermal envelope. If you don’t do this you will be wasting a lot of heat in the attic in winter. This heat will melt snow on the roof and can cause ice dams to form and water leaks that can cause a lot of damage.

A: The question I asked during the webinar was not very clear.  We have a water based heating system with radiators and a boiler fueled by gas.  We also have an air-sourced A/C system with small tubes running throughout the house (a UNICO, high velocity system) without the hanging of mini-split systems in each room.  Is there any way of using an air sourced heating system to heat the hot water in our radiator based heating system (either through the existing boiler or directly to the hot water circulation system)?

Hi Alan, yes is the short answer, you can connect an air-sourced heat pump to a water radiator system. These are sometimes called hydronic systems. But the long answer is a bit more nuanced. These type of air-sourced heat-pump to hot-water systems are made by Jaga, Daiken and Spacepak and other manufacturers. I have never used one so I have no particular recommendations. The hot water in a boiler-driven radiator system is typically at 140F. Air-sourced heat pumps have a hard time getting the output side (whether it is air or water) above about 110F. So your radiators will no longer have that piping-hot feel (which may be good or bad – I have nearly burnt myself on hot-water radiators before). This means that it will take longer to heat your house up from cold – like when you come home from a winter vacation. But, as long as the heat output is matched to your heating load your rooms will stay warm, it will just take longer to get warm compared to what you are used to.

Are you thinking of using the UNICO high-velocity system with a heat pump so it would heat in the winter as well as give you AC in summer? We have a similar system in our rental house and I would consider replacing it with a heat pump if such a system exists. Let me know if you find one. Note, if you do this you will need to insulate the attic on the sloped part of the roof plus the gable ends and add window inserts to improve the insulation on any windows in the attic. If you don’t do this, the heat pump will be leaking heat into the attic in winter (no matter how well you insulate the ducts themselves) and this is not only wasteful but it will melt the snow on the roof which can lead to ice dams and water leaks into the house.

Q: Have you done any calculations (what % higher than air source) to show when geothermal is a better option from a financial sense? A: I have not done precise modeling, but if you can generate electricity from solar panels at 5c/kWh (doable with a sloped south-facing roof), and you can get the wells drilled a lot cheaper than my quote, and you get the federal tax credit then I think geothermal starts to make financial sense.