Heat pumps will use less electricity than resistance heaters. I don't know if the Pioneer will be as good at low outdoor temperatures as some of the bigger names. You have a lot of elaborate calculations, you should be able to calculate the costs including new equipment. Frankly, at the price of natural gas, I am surprised that it is not less expensive to heat the whole place with that then it is with electricity. Have you considered warming up the whole place in the morning, and maybe in the evening, with the gas furnace and switching over to the electric heaters when you are not moving about? That might be a less expensive approach. You could use a wifi thermostat or a standard programmable.

Does your boiler use natural gas? If it does then your heating system is running very inefficiently. I would expect your heating bill to be half of what you stated.

I forgot to ask, what are the deficiencies that your energy audit revealed?

mike_home: yes it's, natural gas boiler.

The audit was performed in 2008 shortly after I moved in. The deficiencies relevant to this conversation were - insulation, air sealing, and thermostat settings. I bought a programmable thermostat, and set heat to run 6-9am and 6-10pm. This lowered my heating bill from $400 to $300 in peak winter months. But that's still way too high.

I believe the larger problem that wasn't captured in the energy audit is radiators. They seem to be inefficient and are placed near windows (which are all single-pane). Some windows also have a/c units, which cause even more heat loss.

Along with ductless a/c, I plan to remove all window units, add more insulation and air seal the house as much as possible.

I would like to know if ductless a/c will use more energy and all this effort will be in vain.

When was your home built?...how would you describe home's insulation qualities?...it's quite typical to place radiators on an outside wall under windows.

What is nat gas cost/therm and electric cost/KWH?....age of boiler and rated efficiency?...when was it last serviced?...it would seem to me that tackling the heating issue should be highest priority over updating AC.

The idea of cutting off radiators with nat gas as the heating fuel and using electric space heaters is a poor strategy.

post back

IMO

You are correct - the ductless mini a/c I have in mind provides heating as well.

My home was built in 1937, insulation is poor (screenshots of audit report attached), boiler is old and hasn't been serviced since I moved in (not the smartest homeowner, I know!).

I pay $0.1099 per kWh and $1.23 per therm (including supply and delivery charges).

On average, I have been using 1,350 therms per year for heating and 750 kWh for cooling. These figures exclude base usage for normal daily function.

This winter, I expect to use less than 4,000 kWh for heating.

I find it interesting from your audit that the most expensive item listed was windows and doors but est savings can only be described as poor.

you failed to answer this question.

"age, size, and rated efficiency of boiler...when was it last serviced?...it would seem that tackling the operating cost of existing boiler should be the highest priority over updating AC"

IMO

I actually do not know details about the boiler. It certainly has not been serviced since 2008, which is when I bought the house. I will try to find those details when I get home tonight.

It's quite obvious...boiler/radiator heat is one of the best and most comfortable and even better with nat gas as the heating fuel. There is your starting point. Get a reputable HVAC dealer who has demonstrated background in boilers and radiator system to inspect your boiler system, tell you exactly what you have and make a recommendation as to a high eff replacement boiler correctly sized.

IMO

What kind of water heater do you have? If your boiler is more efficient than your water heater, you might consider moving your hot water source to an indirect tank fired by your boiler..

I think that you missed my point about heating performance of mini splits in cold climates. Some models retain their performance to a much lower outdoor temp than others. One example are the Mitsubishi Hyper Heat models. The ones you have your eyes on may not do as well, but I don't know for sure because I am not familiar with Pioneer.

Yes, unless your gas-fired heat is horribly inefficient, there is no way you should be able to heat with resistance heat or heat pumps for less coin. I think that you need to check your calculations.

I just looked up that 1 therm equals 29 kWh. I assume that is 100% of the energy in the therm. With your boiler, we have to guess at an efficiency. If we say 80% you get 23 kWh out of a therm. That says that for the same amount of heat, you pay 5.35 cents in gas vs 10.1 cents for electricity. (Frankly, I am surprised that the difference is not greater. Maybe I made a mistake.) As I wrote previously, there may be some savings in spot heating with electric spot heaters, but not heating most of the home that way. You'd have to cut your heat loss by partially heating the home to nearly half. For a heat pump at those fuel costs, it might be worthwhile.

If your window units keep you comfortable enough, you will likely be happy with the cooling performance of mini splits. The good ones are good at humidity control, but you need to have variable speed compressors and blowers for that. They do entail considerably more maintenance than a central air system. For heating, you just have to crunch some numbers to see if they are better than your hydronic system. Keep in mind that raw fuel (electricity) efficiency is only one factor. Lifetime costs of the equipment should be factored in as well. A bunch of mini splits is a lot more complex a system than a simple boiler and a circulator pump.