“Building new house in northern climate… What are the options if trying to stay as green as possible?”

Geothermal!

IMPO

SR

General comment about looking at air source heat pump efficiency: yes, efficiency declines as it gets very cold, and at some low temperature will need to use resistance heat. But what you need to look at is the number of days expected to be below that low-end temperature. So when you say 'routinely', if it's only one day a year on average, it won't effect the running costs that much; if it's thirty days a year, it matters a lot more. So you need to look at the efficiency at different temperature points against the usual weather profiles locally.

(Note it's a bit more complicated - the efficiency changes with temperature more gradually, it's not a simple on-off at the lowest-rated temperature).

I agree geothermal more efficient - it's just a question of whether the higher up-front cost is justified.

And first step in more efficient heating is a better insulated house.

I agree with above post. You need to take close look at efficiencies and fuel costs for various equipment options. That would be heat pumps split or Geo, mini split heat pumps, and even furnace/boilers fueled by propane. Also with those low temps mentioned, I think you might be disappointed with heat pumps as far as comfort and the fact that resistance and expensive auxiliary heat would probably be needed. Put in great building and insulation qualities.

IMO

Also, this may be obvious but not to me - minus 10s and 20s, in fahrenheit or celsius? If you say your location or climate zone would help.

Also, came across this resource for cold-climate heat pumps.

https://neep.org/ASHP-Specification

Short form, there are various industry and research groups working on how heat pumps work in cold climates, what to look for, what to consider, etc. Some of the older standards and specifications didn't even look at performance in colder weather, just assumed it was bad.

Actual products listed here:

https://ashp.neep.org/#!/

The actual products listings give coefficient of performance down to 5F.

There are other helpful resources, website is a bit of a mess in my opinion.

If you post the nearest city I will look up the outdoor winter and summer design temperatures. Other useful information is the size of the house, whether it is one or two story, and the insulation values of the exterior walls and attic.

Is natural gas available? If it is then it should be on your list as heating options.

In my experience, the new mini splits will leave you cold in the very low temps - every night in a Maine winter! Even with your tight house and better insulation, the unit (s) will not keep the interior warm.

For safety (power outage) and comfort add a wood or gas stove, with proper venting and make up air, to the living space.

ulis - so you live in Maine, have R33 walls and have a cold interior with minisplits? Color me skeptical. That being said, a small resistance heat source is not a bad idea.

Does every house that has a winter need gas or wood stove?

The thing you'll notice by looking at those neep product tables above is that the amount of heat output (BTUs) per hour falls as the temperature gets colder. So you may well need supplemental heat for the coldest periods or nights - gas or electric resistance or wood or whatever. This is different from other heat sources, where output doesn't change much. (Also I gather climate difference between northern maine and southern parts and the coast is pretty substantial). Solar offsets fine if you're getting net metering, though.

I'm making no comment about whether/how much additional heat apart from heat pump may be needed - too many specific factors. I like the suggestion of geothermal but that's a question of whether it makes sense in terms of heating load and up-front cost and lots of other specific technical factors.

Re: armoured

“ I like the suggestion of geothermal but that's a question of whether it makes sense in terms of heating load and up-front cost and lots of other specific technical factors.”

This is a ‘Residential’ HVAC forum. People here mostly think in terms of forced air or mini splits. ‘Water’ is only for in-floor radiant or hot water radiators. Water is not often thought of as a solution for renovations or new construction.

“Think Water” as a solution for any situation where most every other solution becomes impractical for heating and cooling. Why? Because water as a heat transfer medium is almost 3500 times as efficient as air when both undergo the same temperature change.

Put another way, a 3/4inch tube moving water is equivalent to a 20inch by 12inch rectangular duct or an 18inch round duct! So what’s easier to install, large ducts where none exist or ~2inch holes for insulated pipes to run water? What’s more efficient, 1-HP blower motors or small, fractional HP (Horse Power) water circulators? A Gas furnace at 97% efficiency (if you're lucky) , or a really inefficient geothermal heat pump at 350% efficiency?

There’s a water solution for almost every situation where forced air becomes impractical.

"Think Water"!

IMPO

SR

"A Gas furnace at 97% efficiency (if you're lucky) , or a really inefficient geothermal heat pump at 350% efficiency?"

You lose credibility with ridiculous doubletalk/non sequiturs like this. These two "efficiency" measures aren't comparable, aren't meant to be comparable, and are apples and oranges. You know that. Do you try to convince and impress people by fooling them? My layman's definitions

Gas furnace efficiency = how much of the heat contained in the burned gas is captured as heat for the system

Heat pump efficiency = With electrical resistance heat defined as 100% efficient, how much more energy can be produced with a heat pump. 300% would be three times as much per unit of electricity compared to if used for resistance heat but of course, that's not a surprise or a magic feat because heat pumps don't produce heat the same way resistance heat devices do.

Are these correct, or close?

fsq, heat transmitted in water through a pipe versus in air through a duct is also not a magic trick.

It is a residential forum, and people think of conventional split systems with furnaces and AC or air source heat pumps in cheaper power areas because they're much, much less expensive than radiant heat and ground source heat pumps. For houses, water is fine for heating, even preferred by some, but requires system duplication for air conditioning that needs ducts.

Most of the US needs air conditioning in homes. I believe that's less true in Canada where you live and whose conditions (including cheaper electricity) you must have in mind with the recommendations you make.

@wherermyglasses: you asked about backup power. Main questions are how much power you expect to need, for how long, and cost of the batteries compared to a generator. I looked at this for my place - heating by gas, separate circuit for essential loads only (boiler, pumps for water, refrigerator, limited light circuits) - and cost of batteries would have been pretty high for only perhaps a day of backup power in cold weather. If your heat is electric, the battery size would have to be even bigger, possibly much bigger, and still time-limited. Cost of a generator is not that high, and can run far longer as long as you have fuel (and functioning).

I'm still considering - lots of power outages but they have been short and mostly planned/non-heating months due to some grid work being done, i.e. just an inconvenience. But if I were preparing for a serious multi-day outage, for me it would be no contest, batteries too expensive. YMMV, battery prices are coming down, just my own experience, do your own research, etc.

Batteries for backup are more expensive and won't be as helpful during long outages. So it does depend on your load and typical length of outages.

Generators are noisy, polluting and may require maintenance.

I am considering a battery backup. We lost power 2 times in the last week. The loads were low and the outages were short. Which also means they weren't a terribly big deal....

We have 1/2 of our outages during snow/ice events. No sun to make electricity and a strong need for heat. We do have a gas fireplace so I would try to mostly survive on that.

Frustrating that our car batteries can't be used....