You probably don't hear much from people who are happy with their heat pumps, because it's boring when it just works.
But, the competence required for heat pump sizing depends on the local climate. If you need more heat than the outside unit can gather, you're stuck with fallback heat, which is usually resistance strips, which is expensive. Some thermostats will call for the fallback heat anytime the requested temperature is 2-3 degrees F above the measured indoor temperature; if you've got a thermostat like that, you've got to be careful how you adjust it, and HVAC installers don't always explain that in ways that the users understand. Lots of people want it a few degrees colder when they're sleeping, but setting that up in the most straightforward way leads to resistance heating in the morning.
You're going to tend to want to windows of conditioned spaces closed, otherwise you're sending your heating budget out of the windows. Heat pumps are usually setup so you can directly regulate the temperature as desired, rather than boilers where it gets so hot that you need to open the windows to balance. If you want to run it with the windows open, you'd need more capacity, and you'd really need to convince your HVAC person. It probably makes more sense to look into a heat recovery ventilation system, which gets fresh air in without losing as much of the heat (or gaining as much heat if you're cooling). This is probably a norms thing.
Insulation helps reduce heating / cooling costs for sure, but if your home is less insulated than the norm, you just need a larger capacity system. That's another place where installer competence comes in. Actually measuring airflow and calculating requirements is unfortunately not very standard, there's a lot of rules of thumb or replacing with similar size units or the neighbor has X so use that. Again, this is workable in mild climates, but if you've got outside temperatures much below freezing, you need a competent installer, as capacity goes down quite a bit as the temperatures go down, and that's also when you need it the most. And, just insulating the heck out of an old home that was built to be drafty can cause issues with retained moisture and mold; it needs to be done carefully and appropriately.
Yeah, if you're accustomed to keeping windows open during the heating season, I think you're going to have a bad time unless you live with a mild climate. Sounds like you're probably on a boiler / radiator system; which probably means you're not in a very mild climate.
You could ask an HVAC company what it would take to be on a heat pump with the windows open, but it's probably going to cost a lot of electricity, and if you build the system for that, when you eventually do decide to close the windows, the system is going to be too big and you'll have comfort issues from that.
Do you have air conditioning? Do you leave the windows open during the cooling season?
I'm in London using a gas boiler like almost everybody here. Our windows are always open in the summer and also during much of spring and autumn to keep the mold at bay and the air fresh.
Heat pumps are trying to compete against very inefficient, yet very powerful, forms of heating.
A 100 year old house might have 12 fireplaces, each of which, when loaded full of wood or coal, can output 10 kilowatts. Thats 120 kilowatts of heat - 500k btu/h.
If upgraded to a gas boiler, that same house might be fitted with a 30 kilowatt system - 100k btu/h
The same house outfitted with a heat pump might expect to get a 10 kilowatt system - 34k btu/hr.
See how we are fitting smaller and smaller heating systems to our houses? Thats because a heat pump's cost scales with capacity, so we don't want to oversize. In fact, a typical house wouldn't even have enough electricity for a heat pump as powerful as those fireplaces!! Whereas a fireplace doesn't really cost any more to make it a tad bigger.
The less powerful heat sources need to run all the time, and will take many days to bring the house up to temperature after being turned off. Even then, they need to be paired with extra insulation to reduce losses.
A typical WW1 'workers house' would have ~5 bedrooms, 10 foot ceilings, ~6 other rooms, and one or two fireplaces in each room.
With no heat circulation system, you would want a fireplace in each room for comfort. Typically windows wouldn't really seal, so you needed the radiant heat.
Other replies have great points. A few of my own (1) Proper install is really important, we're building a software tool to make sizing heat pumps and qualifying ducts easier (2) Having a dedicated smart thermostat means that back up heat strip operation is much better than the normal control logic (3) A well installed heat pump system provides a better thermal environment than a furnace because it precisely matches the load of your home instead of cycling on and off. This lets the surfaces in your home soak to a more uniform radiant temp, and radiative exchange is ~50% of your perceived thermal environment at room temperatures.
I replaced my electric furnace with a heat pump. It takes up the same space as the old furnace, so you're not wasting any space inside the house. There is an outside unit, but we just put it on the side of the house where we don't see or hear it. They are noisy outside, that's one thing they don't always tell you.
When the temps are too cold out, there are still electric elements inside the unit in the house. Sure, that's probably not saving me any power when it's running, but most of the time it's not. It pretty much only kicks in when there's a big temp differential between desired temp and current temp. It's basically like having the best of both worlds. Plus, as a bonus, I got A/C for the summer to offset all my winter savings.
I've no horse in this race (not a homeowner), but Technology Connections has made a series of videos advocating heat pumps, most recently this one: https://www.youtube.com/watch?v=CVLLNjSLJTQ
The gist is that heat pump technology is continuously getting better at working in cold conditions, so if the horror stories are more than 5-10 years old they may not reflect the current state of things, and in extreme situations resistive heating can always be used as a backup.
Heat pumps are "just" air conditioners that point the other way, and AC is extremely common in the USA, so I'd doubt that the competency required is exceptional.
They aren’t a drop in replacement. Heat pumps need large ducts or you won’t have enough flow because the air in the ducts is not that much hotter than outside air. Delta t is low
- Enormous energy bills because under some conditions (cold weather?) heat pumps use a lot more energy than expected.
- Heat pump equipment and radiators taking too much space in small homes.
- Cold homes and/or a requirement to keep windows shut because heat pumps just don't generate enough heat.
- Only suitable for very well insulated homes.
Am I only reading this because people are more willing to speak up when something bad happens to them than when everything works as expected?
I worry that heat pumps are only viable under perfect conditions, installed by exceptionally competent engineers that hardly exist anywhere.
Please tell me it is not so! :)