@Rosesandstars
was discussing your post with my DH at lunch. He offers the following (apols for being long and digressing a bit but I agree with everything he says)
If your post said "AIBU to hate living in a cold house?" then no, (almost) nobody would like that. But you're not living in a cold house strictly because it's got a heat pump.
Consider this; if I said "AIBU to hate it when the food in my fridge goes off?", people might ask what the thermostat was set to, if the seals were damaged, if it had been cleaned recently. I doubt anyone would start ranting about heatpumps and how they don't work, because most people have experience of fridges, freezers or air conditioning. They all use the same basic technology and physical principles as the ones used to heat houses, but no-one complains about them because by and large they work as expected.
In Scandinavian countries, heat pumps are commonplace, normal, yet these are not places known for their mild winters. They demonstrably do work in cold conditions. So why is your house cold?
The simple answer is that whoever fitted the heatpump either didn't know what they were doing, or didn't care about whether the end result would be any good, or possibly both. If you want something or someone to hate, cowboy plumbers would be a good start.
The (rather) more complex answer is that gas boilers and cheap gas have allowed the building trade to be, for want of a better word, lazy. Most gas boilers are hugely oversized, outputs of 25-30kW are not uncommon (for reference, an ordinary hairdryer is 2-3kW). This is mainly so it can can heat water on-demand - so you can't "run out" of hot water - while avoiding the need to fit a tank. It's convenient for the user, but it also saves builders money (less plumbing, no tank). On top of that, builders don't need to size a heating system properly, they just chuck in a powerful boiler and let cheap gas do the work.
Hot water aside, almost nobody actually needs to pump 25kW into their homes, unless you like to set your thermostat at 28C or you live in an actual, literal mansion. But such high outputs (and the fact that gas has historically been so cheap) has meant builders can just install small cheap radiators with pipework barely big enough for drinking straws, buildings can be poorly insulated and leaky, and people just compensate by running their heating at 60-70C. This is not efficient even for a gas boiler, but again nobody cared because gas was cheap.
Our house is an unremarkable 15yo detached. It has cavity and loft insulation, but is by no means "super well insulated". The windows in particular were pretty draughty even when closed!
Our installer did a survey, got the dimensions and materials of the house, and got a heat loss calculation done for each room. Off that, we then sized the radiators for each room; the installer started off assuming a relatively low maximum flow temperature (eg 40C) since this is most efficient (aka uses least energy = cheapest to run). If what's there is already big enough, great. If not, you either need a bigger one, or you'll need to set a higher flow temperature. That will make your heatpump less efficient, but you'll save money on new radiators. Swings and roundabouts.
We ended up replacing a number of radiators, moving some around internally, and removing a couple as well. And installed a large water tank. It's taken some tweaking but the house is always a pleasant temperature, and our bills are lower than they were with the old gas boiler, while we are more comfortable and we've yet to experience a 'no hot water' situation.
If whoever did your install didn't do their due diligence and follow through on the necessary changes, you'll have a shit experience. Most commonly the radiators are left too small, meaning that there isn't enough surface area to transfer heat energy through. You can either crank up the flow temps (which will help but will cost a fortune, and still may not work that well) or freeze. Or in the longer run, you could consider getting a heating engineer to have a look at the system. It could be that you could change some of the radiators and have a system that would work much better.
Lots of people will say "I can't afford all this" and that's fair, this shit is expensive. There needs to be comprehensive support from government to get us off fossil gas. This also has to include planning rules, and training support for installers, since that is also a major bottleneck. Some people will say "I could afford it but I'll never make my money back". To those people I say "no, you probably won't". I've mentioned over and over how we are in this mess because many recently built houses have been built with an eye to making the most profit for the builder, not making them economical and comfortable to live in. Be angry with the large house builders, they have consistently lobbied governments for lax energy standards. They got the profits, we get the poorly insulated housing and high bills.
Separately there has been minimal support for people to make energy efficiency upgrades to older homes. What little there was got binned by Tory governments in 2012 or so. So now we have a huge backlog of housing stock that will need expensive retrofit to be able to use heatpumps economically.
Yes as a country we could just "stay on gas" for heating, but we don't want to be beholden to the likes of Putin or the Gulf states when it comes to energy sources. The UK has an outsize responsibility for historical emissions, particularly when we consider things like all the logging done in former colonies for the profit of Empire. So we really should be leading the way when it comes to getting away from it.