A: The easiest way to reassure yourself about indoor air quality is to measure it using an inexpensive indoor air quality monitor. Ours is from Foobot but there are many others. Our indoor air quality is consistently excellent. Our insulation is a mixture of fiberglass and ISO board panels which are essentially spray foam in a board. I do not know of any indoor air quality issues arising from any of the common types of insulation like fiberglass, cellulose, spray foam, ISO board or rockwool. Concerns over off-gassing from insulation usually relate to urea formaldehyde foam insulation. The use of this was banned in the USA in 1982.
Q: Would you suggest installing insulation in basement ceiling even if the basement walls are insulated?
A: If the basement space is used as living space (and heated) then there is no need to insulate the ceiling if the walls are already insulated. It will be better to just install a thick pad under the carpet – and that will keep your feet warmer too! If the basement is not used as living space and is unheated then it makes good sense to insulate the ceiling so that you are not waseting your heat on your luggage.
Q: I want to put in a heat pump and have a gas boiler with a how water heater – is this recommended
A: You could replace the hot water heater with a heat-pump hot water heater, replace your AC unit with a heat pump for heating the house and leave your gas boiler in place for heating the house on bitterly cold winter days.
Q: For homes that already have solar, it seems like heat pumps would be a tougher sell, because they’re already getting the advantage of reduced electricity. How does the ROI of heat pumps change when the solar is already in place and electric bills are already very low?
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.
Heat pumps increase your house price 4-7%
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.
A heat pump for a greenhouse?
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!
Q: Heat pump hot water heaters and bacteria.
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.
Q: back in the 80’s when I had heat pump the exit temp was in the mid 90’s so even if you were sitting in front of the air duct, you perceived the warm air as cold – it was uncomfortable heat. Do the new systems provide a higher temp of the output air?
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.
Q: Do heat pumps work with water heaters, are they efficient?
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.
Q: My hot water tank has broken, what do you recommend?
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.