Try heat pumps.
Denver pretty much never gets that cold. Most of the continental US doesnt ever get that cold.
You go below 0c for a month, enjoy your baseboard-levels of efficiency.
Some anecdata: Neighbor is on heatpumps and has a comparable house (in terms of size) to mine. My house is significantly older than his, worse in terms of insulation, I have a number of old leaky windows, all of his are brand new, etc. I primarily heat with wood, with a oil furnace backup that runs a forced hot air system. His bill for four straight months last winter for electricity was 800 dollars a month (3200). My total for oil+wood was 2400 total and I still had firewood left over.
He also got to deal with the fun of heatpumps just not working in the dead of winter because it was too cold outside.
I'm sure there'll be a lot of "oh it's the type of heatpump" "oh it's the installation" thing, but he isn't the only aquaintance I have who has seen absolutely diddly-squat for heating efficiency when using heatpumps. Around these parts, if it isn't setting something on fire, then you're probably doing heating wrong.
>Nordics
The average low winter temps in Stockholm are what, -5c? Oslo doesn't really get below -10-ish? Non-northern nordics are an indicator of approximately nothing in this discussion. :) Finland loves their steam/hydronic heat, which I will guarantee isn't being run off of heat pumps.
Anything that's closer to the ocean is going to have a significantly milder winter than going proper north.
> Finland loves their steam/hydronic heat, which I will guarantee isn't being run off of heat pumps.
In my case, the steam is being generated by the 240V electric steam generator that takes power from my 7kW ground mount solar array.
Where I live, heat pumps are usually still not cheaper per month. And even when they are, the amount people save doesn't make up for the added cost of a heat pump. If you want to be green, get a heat pump. If you want to save money, don't.