That's not necessarily true now the newer systems can go to as low as -15F which in the north only happens for a few hours a year so still a reduction in heating gas/oils needed

I got a quote last year as my furnace is original to the house (33 years old) and we don’t have AC.

It was going to be $25,000, $5k of which was installing new ductwork because the existing ducts aren’t insulated enough.

Easy pass. I’ll wait for prices to (hopefully) come down.

First off, as the other poster replied, that isn’t true about modern heat pumps. They continue to work below freezing, and many support an “eheat” resistive heating mode, obviously only good if you still have electricity, but that’s true of all heat pumps. Generators or solar+batteries become much more important.

But the beauty of heat pumps is that you don’t need to install ductwork. Look at mini splits. You can do zoned or single room installs. No ductwork required. One of the huge upsides of mini splits are you do get “instant” zoning. You can stop heating and cooling unused rooms to a human comfortable temperature.

You can also get systems that retrofit into existing forced air ductwork.

I wouldn’t be surprised if someone made or will make a heat pump water heater for hydronic radiators.

You can also run the element that is typically outdoors inside if you have enough space in a basement, for example, which stay a pretty consistent temperature all year long.

Heat pumps stop working at 20-30F

Yeah crappy ones. This does not apply to the ones designed for cold climates. Mine still beats electric radiators in efficiency at -22f

That is refrigerant dependent. For example R744 (plain old CO2) works well efficiently down to -4F, -20C and down to -40C/-40F just with some efficiency drop.

Main issue is CO2 needs a constant high pressure heat pump system, since it needs to be highly pressurised to be fluid at all. In ambient it sublimates (goes straight between gas and solid aka dry ice).

However that is a solved issue. Working CO2 heatpumps are off the self commercially available these days. Just still little more expensive as I understand. However prices should come down with production economies of scale, upon CO2 taking over due to pollution, toxicity, flammability, green house considerations. He nastier chemicals weren't used for being all the ways superior, but due to it being easier to make the heat pump units (be they running in heating or in cooling) due to lower pressure requirements.

Since CO2 and ammonia were the original refrigerants. Used in large ice production facilities early on, where their specific needs weren't issue even for earlier technology. Large, purpose built, stationary industrial facility had no problem accommodating the needed massive pressures by just really massive and heavy pipework.

However these days the propeller head people developed micro channel tubing and heat exchangers to keep the high pressure CO2 in control.

In Scandinavia we run ours down to -4F or colder. Efficiency goes down but they are still better than 1:1 until then.

I’ve never seen anyone using their furnace to run hot water. Radiator water loops are closed loops and I’m sure you wouldn’t want that water to be used for anything you’d use hot water for.

I think it’s mostly a factor of ACs weren’t historically efficient. They were all on or all off. In the more recent designs that are ultra efficient they use variable speed compressors.

They were also historically less reliable than a furnace and certainly more difficult and complicated to service.