Heat pumps require some domain-specific knowledge to build a system that costs less than gas for the same building (the crossover point is near a seasonal average COP of 4.0 at UK's gas and electricity prices, as mentioned in other comments SCOPs of 4.5 are very possible). Yet there are subsidies available and installers without the knowledge (who would normally be installing gas systems) are installing them basically without sizing radiators correctly or by doing things that reduce performance (big buffer tanks, lots of zoning, extra pumps that are unnecessary, etc.).
So there are lots of horror stories of companies installing systems that don't work very well and cost a lot of money to run, which makes people think heat pumps are crap. But usually people like Heat Geek trained installers can fix such systems without changing the equipment - often both providing more comfort than gas (less thermal cycling because heat pumps with inverters can modulate their output more precisely instead of hard switching on and off) and costing less to run than gas.
I see, thanks. This provides a counterpoint to the sibling comment of "they don't perform but everyone blames the user for doing it wrong", but also sounds true, so hopefully as installers learn more about how to correctly install heat pumps, they'll perform better.
COP is Coefficient Of Performance, basically the heat they produce divided by the electricity input, so a COP of 4.5 means that 1kW of electricity produces 4.5 kW of heat (it's taking heat from the environment so you can say a COP of 4.5 means it's running at 450% efficiency, but that's only in terms of electricity use, not actual overall efficiency - but electricity use is what we care about).
COP is only an instantaneous measurement though, and changes depending on the outside temperature. So if you need heating for five months a year, and it's usually exceeding COP of 5 for 80% of that time but dips down to a COP of 3.0 on the three or four coldest days of the year, it's not really correct to say it's either >5 or that it's 3.0 - so SCOP is used as a 'seasonal' COP that is averaged over a longer time period, so you can compare different systems over the longer term.
COP (coefficient of performance) is taken at a full load condition with specific indoor/outdoor conditions.
SCOP (seasonal coefficient of performance) is a weighted average of performance at different load conditions that represent different outdoor conditions based upon an average binning of weather conditions.
Most if not all energy/green subsidy schemes in the UK in the past couple of decades resulted in tons of cowboys rushing after the gold, and doing a terrible job and even causing serious long-term damage to the property.
No different this time round I imagine.
It's so infuriating - literally handing money to conmen
Maybe. However a heatpump sized to cool your house in summer cannot heat your house when the temperature is below about -3C. The heatpump might be able to produce heat to -25C, but it is too small to produce enough. Thus my system (in the US) that I just paid a lot of $$$ to install last fall leaves me using the backup gas heat a lot more than I wanted last winter which is disappointing. (It did get below -25C last winter for 2 days so I'd need that backup heat anyway, but I was expecting only 2 days not most of a month)
A properly sized system will be based upon the worst of the heating or cooling conditions.
Luckily an inverter heat pump can run down to about 25% full load so even with them coupled and in an imbalanced heat/cool environment you can still see good performance year round.
British note: UK govt subsidies for some insidious reason are not available to "reversible AC" style systems, so the dominant form here is air-to-water.
I had mine fitted last year. Retrofitted to existing radiators with 8mm pipework. With natgas backup/hot water boiler. At the end of this month I intend to go back and correlate the bills against the previous year (both kWh and £), because like a lot of discussion in this thread I think the installers have made some poor decisions. There's too much poorly insulated external pipework.
The table in there assumes pretty high quality insulation and the neoprene-looking stuff doesn't meet that standard so would have to be thicker. Note that the way the performance of pipe insulation varies non-linearly with the pipe and insulation radius so it's a bit unintuitive.
How do I know? I had the same problem with my installers.
I have this outdoor unit https://cooperandhunter.us/product/ch-hyp36lcuo. This past winter the temperature dipped into -20C (-11F), had no issues maintaining temperature in the low 70s in the house. I was running them in heat pump only mode (resistive strips were not used).
In the summer our temperature regularly reaches into 90s (above 30C) and the house is very comfortable on those days as well with the same heat pumps
Hmm, that's interesting, we have fairly large temperature swings (typically -15 C in the winter to 40 C in the summer), so it'd be interesting to see if the heat pump could replace the AC unit and the gas heating.
I'm in a similar zone and replaced (delivered) propane with a ground source heat pump 2 years ago. Constant temperature indoors (3C warmer in summer than winter) with plenty of AC capacity to spare. Breakeven is about 5 or 6 years.
They work okay in my area for -1C to 46C, imagine for your range maybe you just get a model that has improved heating over a basic one, whether that means ground source, more stages, or a heating element.
I've watched a few videos of his and I'm not sure I'd characterise him as entirely skeptical of the technology as a whole, but more skeptical of the government incentives to retrofit.
He argues in one of his videos that there aren't enough qualified installers who actually understand heat pumps, and the government incentives are encouraging cowboys, basically, to take the government cash and provide unsuitable installations. Then secondly, a lot of the insulation installers also don't know what they're doing and are creating damp problems by neglecting ventilation.
Even as someone who is a huge fan of heat pumps, it's hard to disagree with him. There are a lot of difficulties with retrofits in the UK, where we have a lot of old terraced housing stock with poor insulation, no mechanical ventilation, and small gardens. Then on top of that, there are almost no tradespeople who actually understand the technology or why that housing stock is unsuitable without extensive improvements.
To be frank, even regular gas plumbers are shocking here. They don't install correctly rated systems, don't set the temperature correctly and don't enable the weather compensation functionality that is built into all modern combi builders and can save you 30%. They just install an over-sized boiler and whack the temperature up to maximum. At least it keeps the house warm, at the cost of inflated bills. That's without getting into the FUD about chemical water softening (and use of magic magnetic "water conditioners" instead), continued use of loft header tanks and not understanding how to improve or balance water pressure.
No they don't and it's kind of like agile everyone tells you it's not done the right way otherwise it would work. But when is sold it's sold as is it's great.. Very deceiving for customers
