Rolling up sleeves...
First, we go to the fuel cost calculator on this site:
https://www.hearth.com/econtent/index.php/articles/fuel_cost_comparison_calculator/
and we put in $300/ton pellets and $0.11 kWh elec, and we get that one million BTUs of delivered heat costs:
$26.57 using pellets and $32.23 using electric resistance heat (e.g. a cheap electric space heater). First thing,
your elec is cheap (hydro) and your pellets are expensive. Your pellets ARE cheaper than running a cheap electric
space heater, but not by much--about 18% (26.57/32.23 = 0.824).
A Heat Pump will deliver more heat than a space heater using the same elec by its coefficient of performance,
or COP, that decreases with outside temps. Whenever the COP is >32.23/26.57 = 1.21, the HP is cheaper to run
than the pellet stove. For the high-eff units you listed, I expect the real COP (assuming proper install, defrost, etc)
would be >1.5 down to -10°C. Looking up climate tables for your location, it looks like your January ave temps
are closer to 0°C, so it is likely that a (big enough) HP could heat you cheaper than pellets for nearly all of your
heating season.
In this (cheap elec) situation, the usual suggestion is to size the HP to meet your average January demand. Paying
for a bigger unit to cover those rare super cold days doesn't pay (cuz you rarely use it). Similarly, buying a smaller
unit will save you less money (by requiring more expensive backup), and the cost of a HP unit goes up more
slowly than its output capacity (e.g. a unit putting out 50% more BTUs might only cost 30% more to buy up front).
So now we come back to demand. If a 40lb bag costs $6, and the calculator told us a MMBTU cost $26.57, then
it takes 4.42 bags to make a MMBTU, or 1 bag is 225 kBTU. If we say you use 1 40lb bag per day in typical January
weather (0C), then we divide by 24 hours to get about 9500 BTU/hr. So, if you really use about 1 bag/day in typical
January temps to keep your house comfortable, then you want a HP that puts out that much at your typical January
outdoor temps. How much do your listed units put out at 0°C I dont know. My slightly lower eff HP (also R410A) puts
out 46 kBTU/h nominal maximum (at 47F) and output drops to 37 kBTU/h at 32F. If we estimate that your listed units
are similar, then they would put out about 37/46 or 80% of listed maximum at 0C. In other words, you need a unit
with an output of 10 kBTU/0.8 = 12,500 nominal max BTU/h to replace 1 bag of pellets/day heat demand.
Of course, you will have to adjust these numbers--your demand seems kinda low (!), but maybe you have a small, very
well insulated bungalow that you keep on the cold side. If you really use >1 bag in typical January temps, then you should go
proportionally bigger than a 12 kBTU/h (nom) unit. As for payback, if you can get a seasonally averaged SCOP of ~2
(likely for your mild climate) then your average cost per HP BTU is about 40% lower than your pellet costs in this plan
and your annual savings would be close to 30-40% of your current annual pellet bill. It will likely be more convenient to operate.
Potential concerns:
--control. You will have two separate heaters with two thermostats. You will have to set them a couple degrees apart
so one backs up the other? Not a big deal, but some would consider this a hassle.
--sizing. We could be wrong and you get a unit that is too small or too big. Too small and you are still running a lot of pellets
and not saving as much as you could have. Too big and your 'payback' takes a lot longer.
--future fuel costs: will your elec go up a lot in your payback period? Can you find a cheaper pellet supplier on the internet instead?
In the end, if your average January temps are really around 0°C (maritime climate), I suspect that you will be quite happy with
the convenience and $$ savings of a HP relative to pellets.
