All Forum Posts by: Seth Borman

There isn't such a thing as a "second SFR" it would at that point be a duplex so you could do two ADUs after the fact, which actually sounds like a solid idea to me.

Why are you focusing on resistance heat? No one is suggesting that to anyone. 

 See above. Some inverter heat pumps still have resistance heating. Most don't. You should have a backup, but you need one if you use a gas furnace as well because they require electricity as well. In fact, a furnace requires like 800 watts for the blower motor and a small mini split might use twice that to provide heating.

If you do use electric resistance heat you probably won't use much. A friend is heating houses in Cleveland with 2-3 tone heat pumps and they use about $200/yr of electric resistance heat. The total bill is generally about the same as gas, after the gas meter fee is considered.

Heat pumps don't generally "make" heat, they just move it. Just like how your refrigerator doesn't cool anything, it just rejects heat back into your house.

In practice, that means a heat pump uses 1/2 or 1/4 the energy that resistance heating will use. Which makes % of efficiency the easiest way to communicate the efficiency of heat pumps compared to gas. Comparing HSPF to AFUE doesn't make any sense.

The average low in Denver is 17°, which is super convenient because that is one of the temperatures that heat pumps are tested at.

At that temperature, an air source cold climate heat pump is taking one unit of electricity and converting it to two units of heat.

Your typical gas furnace is 80% efficient. A heat pump is 200% efficient. If the gas is being burned in a 60% efficient turbine, transported with a 10% loss and used at 200% efficiency then you're using less gas with a heat pump than you would by just using gas, and that's on the coldest day of the year. When the temperature is higher the heat pump will be twice as efficient.

Keep in mind that many inverter heat pumps don't have resistance heat, although some will have a crank case heater that uses a lot of power.

 I don't see how. It removes a utility that otherwise would have to be included in new development.

I've even run into this on a flip. Getting the gas repiped is a huge waste of money. More so for a whole new building. And it isn't cheap, either.

 It's a lot more efficient to use electricity for heating space and water than to use gas directly. For space heating, an inverter heat pump is more efficient than a gas furnace until the temperature falls below 20° or so. That's most of the year.

Heat pump water heaters are much more efficient. Gas units are often only 60% efficient, while heat pumps are more like 400%. When you discount that for generations and transmission losses, the heat pump is still more efficient.

In fact, someone (Redwood Energy) did the math and they claim that a HPWH is cleaner in all senses than a gas water heater, even if your power mostly comes from coal.

I think the net zero thing is taking this conversation in a weird direction. There is no need for rooftop solar to make electrification work, and work well. The issues are all around making cold climate heat pumps work (which means a well sealed and insulated house) and not putting solar on the roof.

A well built house that meets the Zero Energy Ready Homes standard costs like 4% more than a code built house (which is not insignificant) but also costs less to operate than a code built gas house.

Unfortunately that 4% doesn't pay for itself in ways that mortgage lenders recognize. We still don't have proper ways of measuring home energy consumption for the mass market.

Yes, a heat pump will work in your climate.

Attic is better, but inside the conditioned space is best. Lots of people use spray foam to seal the attic and then put the HVAC there.