| Q: Was a pressure test conducted on the building and ducts to determine their leakage rates? A: No, but I sealed the holes with aluminum tape so I think the system is pretty good. |
Q: Before the heat pumps were installed, was a manual J & manual D conducted to properly size? A: No. But remember this was a retrofit and we already knew that the old system had sufficient heating and cooling output to create a comfortable house. Since I was significantly reducing the heating and cooling load with the fab four, I was very confident we had enough heat and cool in the system. |
| Q: My understanding if you do not size the HP system using manual J & Manual D and the building and duct leakage are not verified, then NO unit will meet loads. A: Not true, see above. |
Q: Why not electric backup heat?
A: Electric back-up heating is feasible, and many contractors push it as the source of back-up heat when heating with heat pumps. But they are not paying the bills. Using utility electricity at 23c/kWh of electricity to run an electric resistance heater means heat would cost me 23c/kWh of heat in the house (electric-resistance heating elements are 100% efficient at converting electricity to heat) but my oil furnace costs about 8c/kWh of heat in the house. Natural gas costs about half this.
Q: When we calculate energy costs of high efficiency natural gas furnaces vs heat pumps, the furnaces always win out over HP operational costs. On-site Solar is not factored into this however. Not everyone has the cash on hand for adding solar nor qualify for tax credits to offset these installation costs. Q? How to manage lower (not necessarily Low) income families with this program?
A: If the electricity costs more than about 12.5c/kWh then the natural gas will be cheaper, see the answer above. In most of New England and the West Coast electricity is much more expensive than this (it is 23c/kWh for us). In these states you will need solar and a heat pump to both save money and cut your carbon footprint. Part of the reason electricity is so expensive in these states is because the electricity bill includes many subsidies for energy efficiency, solar panels and heat pumps. These subsidies include generous net-metering tariffs, generous solar panel and battery subsidies and low-interest-rate or zero-interest-rate loans, which are often even more subsidized for low-income owners. The best way to cut bills and carbon footprints in low-income communities is to use these subsidized loan programs. If the homeowner does not have a credit score high enough to get a loan, then a leasing arrangement for the panels is always possible. These leases can be very expensive for the homeowner but in the last year or so I have seen lease rates come down, making them at least reasonable options if the homeowner can’t get a loan. In a band of states in the middle of the country from the Dakotas to Louisiana electricity is about 10c/kWh and so there is little money to be saved with solar panels. For homeowners in these states, it will be cheaper to heat with a heat pump than to heat by burning natural gas. It will also be very cheap to run an electric vehicle.
Q: Would a mini split heat pump help to dehumidify a basement?
A: A mini-split heat pump head (i.e., the part that is inside the house or basement) WILL dehumidify the air inside the house but only when it is operating in AC mode i.e., during the summer months. Since basements are generally cooler than the rest of the house, it may not be operating as an AC unit very often and so it may not actually be dehumidifying the basement much at all. In the winter, when it is operating as heater it will not be dehumidifying the basement air.
How effective this is for you is going to depend on what the source for the humidity is in your basement. If the humidity comes in summer (which is quite common because warm humid air enters the house and then condenses on surfaces in the basement because the basement is colder than the rest of the house), then the heat pump will dehumidify the basement air but only when it is in AC mode, which as I mentioned it probably is not doing very often even in summer. However, if the source of humidity in your basement is due to rising damp, i.e., from a high-water table or from rainwater leaking in from the soil then this tends to happen in winter when the ground water is highest or we get rain on top of thick snow. In winter the heat pump will be heating your basement. So now you will have warm humid air in the basement. Warm air rises. Humid air rises. Warm humid air really rises. When this warm humid air contacts a cold roof surface it will condense. This will lead to mold and rot. This is a common problem in cathedral ceilings. Because of this, I think relying on a mini-split heat pump to dehumidify your basement is not a good idea. I think you will be much better off installing a heat-pump hot water tank. These dehumidify the basement air whenever they are heating the hot water, which is year round. Heat-pump hot-water tanks are much cheaper to run than fossil-fuel hot-water heaters. The dehumidification comes as a side benefit, but in my opinion, it is a major benefit. If you don’t want a heat-pump hot-water tank, then just getting a dehumidifier will probably do the job. Dehumidifiers provide a small amount of heat in the basement too.
Q: Also, do you have any thoughts on whether cold climate heat pumps work well? I also have oil heat, and am considering either replacing it entirely with a cold climate heat pump or getting a heat pump that can work with my oil furnace.
A: See Chapter 2 in the book. I recommend keeping the furnace and replacing your AC units with heat pumps. Heat pumps cost less to run if you power them with solar panels. See below for the likely difference to your heating bill and carbon footprint from adding heat pumps:
Adding a heat pump will have dramatic effect on a home’s heating bill and carbon footprint, but the effect varies considerably depending on what heating fuel is currently being used and what the source of electricity is for the home.
Effect of adding a heat pump:
| If currently heating with natural gas | If currently heating with heating oil | |
| If using Eversource or National Grid electricity (at 23c/kWh and 0.87lbs CO2/kWh) | 150% increase in heating bill 10% cut in carbon footprint | 25% increase in heating bill 45% cut in carbon footprint |
| If using Municipal Light and Power electricity (at 14c/kWh and 0.87lbs CO2/kWh) | 50% increase in heating bill 10% cut in carbon footprint | 25% cut in heating bill 45% cut in carbon footprint |
| If using Rooftop solar panel electricity (at 8c/kWh and 0lbs CO2/kWh) | 10% cut in heating bill 100% cut in carbon footprint | 50% cut in heating bill 100% cut in carbon footprint |
This assumes that the heat pump achieves a year-round COP (coefficient of performance, or efficiency) of 2.3, which is the average found in a review of the work of several researchers on Mitsubishi, Daikin and Bosch heat pumps in New England. Both ducted and ductless systems were included. In general, ducted systems had higher COPs than ductless systems and Mitsubishi had the lowest COPs, as low as 1.3 in one case. The manufacturers claim COPs of between 3 and 5 for these units. None of them perform to the manufacturers’ specifications under real-world year-round conditions in New England.
Q: Can you explain how the heat pumps are fueled by oil or gas or electricity?
A: It takes electricity to run a heat pump. There is no fuel. A heat pump is like a water pump, it moves heat from one place to another just like a water pump moves water from one place to another. A water pump does not create water and a heat pump does not create heat. A water pump needs electricity to turn the motor and a heat pump needs electricity to turn its motor too. When I calculate the cost savings from using the heat pump it is the savings on the heating oil bill less the cost of the electricity needed to run the heat pump. The same is true for the carbon footprint.
Q: A heat pump runs only on electricity — do you recommend a generator for electrical outages?
A: Where we live in Dover a generator is standard issue because we get frequent power outages in winter. However, no generator will produce enough power to run your heat pumps. This is one good reason to keep your fossil-fuel furnace when you add a heat pump. The back-up generator will run the circulating fans so the combination will keep you warm. I have recently bought a battery to replace my defunct back-up generator. The subsidies are very generous on batteries in MA right now, so if you are considering a back-up generator now is a good time to consider using a battery instead. Please see other answers on batteries.
Q: Do heat pumps remove humidity in the air?
A: Yes, when in cooling mode. In New England the only time we need dehumidification is in the summer when the heat pumps are operating in cooling mode, but in Seattle where is it cool and humid you might still need a dehumidifier in winter, although some heat pumps (my Bosch ones for instance) will temporarily go into cooling mode even in winter time if they need to to reduce the humidity.
Q: how loud are the heat pumps?
A: The noise level inside our house has dropped considerably with the new heat pumps. Outside the house you cannot hear the Bosch units at 50’ away and the Mitsubishi units are even quieter.
Q: I installed heat pumps around 2010. Between November and March, they are MUCH more expensive for heating than my natural gas furnace. Are 2021 heat pumps sufficiently improved that I will be able to use them all winter? Would I need to replace both the indoor unit and the outdoor compressor, or only the latter? What questions do I need to ask to be sure replacing my current units makes sense?
A: If you are using utility electricity at around 23c/kWh then heating with heat pumps will about increase your heating bill about 150% if you had previously been heating with natural gas. This fact never seems to get mentioned by either heat pump installers or heat pump advocates. Even if you are heating with heating oil, your bill will increase about 25% by switching to a heat pump on utility electricity. The key to cutting your bills AND carbon emissions is to generate cheap solar electricity from your roof. Doing this will cut your heating bill (if you are on natural gas) by about 10% and if you are on heating oil it will cut it about 50%. In either case your heating will now have a zero-carbon footprint. You do not need a new heat pump. You need solar panels.