Air source heating

Yes Storage heaters are cheap to install, and expensive to run. ASHP can be 10K to buy the unit.

A traditional heat pump AC system would have lower capital costs and do away with the UFH requirement.

I can see the attraction for small scale use when resistive electric is the only other viable option.

Well, the first thing to say is that it needs a mindset change: combustion-based heating is about making a small amount of very hot stuff and then spreading that heat around. Heat pumps generate larger volumes of cooler stuff. This means that some things that make sense for combustion (eg microbore piping) don't for heat pumps.

Next up are a category of things which could be described as 'installer error'. Unlike combustion, heat pumps have a smaller range of power outputs they're happy with.

A lower heat output means a slower temperature ramp up - the unit runs for longer, but that's mitigated by having insulation to keep the heat in the house. Instead of turning on the heat for a quick burst when you get home, you leave it ticking along when you're out and you only pay costs for losses through the insulation. It's less good to leave windows open.

If you try and demand too much heat out of them, many have a backup resistive heater. This is designed for occasional days in the depths of winter when efficiency falls, but an undersized heat pump may rely on the resistive heater too much - causing high bills. Our installer puts this on a manual control, so you're at least aware of what's going on (and we'd just burn wood on those days anyway). A number of horror stories have been people moving into newbuilds with heat pumps installed and no guidance on how to control the system (see also that mindset change). Some of those newbuilds had funky ventilation systems that were installed wrongly, trashing their insulation.

If the heat pump is oversized, it still runs but less efficiently, affecting your COP.

As far as a retrofit goes, that cooler water means you may need a radiator upgrade if you don't have UFH.

Therefore a key part of installation is the heat demand and loss calculations, which require a more skilled installer than just sticking a finger in the air and picking a size of boiler.

COP is something you don't really find out until you have the system installed. I've heard various sources but think 2-3 is a sensible range.

Noise: the fans hum, but a lot less than our oil boiler firing

Servicing: there's fewer people who know what they're doing compared with gas plumbers. This is improving. In other countries everyone has an airconditioner, so there's nothing fundamentally new here.

Electricity v oil/gas prices: this is really hard to judge. Oil is cheap at the moment, but I suspect that isn't going to last. With a solar+battery setup you may be able to power some of the heatpump load in spring/autumn (and hot water in summer too).

Theo

nearby neighbour living in a 1976 4 bed detached house had this installed. (Air to Water).

They had to replace all 8 rads with triple-panel finned rads at £300 per rad (that was over 12+ years ago).

They stopped using their Potterton Supreme gas boiler at the same time but then found it was impossible to get anyone to 'service' their central heating system because no-one knew what they were supposed to do.

I asked her what it was like in winter, and her reply was "i'm freezing all the time". Luckily this house had had an external class 1 chimney added by the 1st owner so her other half could spend lots of his time in winter collecting wood scraps to burn.

The compressor is the size of a US-style double fridge but it is on a North facing wall so permanently in shade. I suspect this makes a big difference because here in Sussex the solar gain in winter is very noticible. On a really cold day, even with bright sun, the air at the back of the house is still cold.

Oh yeah. If only it would.

The kensa gshp doesn't modulate, they're either full on or off, seems to imply buffer tanks to underfloor pipework may be needed to stop rapid cycling.

Hi I had an LG Therma Split system fitted nearly 3 years ago to replace a coal fired boiler. What do you need to know?

how noisy is it (from inside the house)

Would it keep a light sleeper awake in an adjacent room?