I dont understand how heat output from a heat pump vs heat output from a gas / oil / wood burner / resistive heater are at all different.
Heat is heat, a joule of heat output by the system is a joule of heat ... or am I missing something?
Heat is heat, a joule of heat output by the system is a joule of heat ... or am I missing something?
A gas/oil/wood burner are not 100% efficient in creating heat, and release carbon into the atmosphere.
A resistive heat is at most 100% efficient: all the electrons go to making the coil glow, like old school light bulbs. So 1 kW of electricity is 1 kW of heat (which has some BTU equivalent for old fashioned folks).
A heat pump does not create heat, but moves it from one place to another with refrigerant and pumps. So 1 kW of electrical usage can move 3 kW of heat at times:
* https://en.wikipedia.org/wiki/Coefficient_of_performance
* https://energyeducation.ca/encyclopedia/Coefficient_of_perfo...
So if you input 1 kW of energy, do you want 0.9 kW of heat out (carbon), 1 kW of heat out (resistive), or >2 kW of heat out?
Setting aside capital costs that's going to cost you 7kWh per hour of heating. An oil boiler will cost 20kWh per hour of heating.
If your oil costs 40c per litre/$1.50 per gallon and each litre delivers 10kWh, that's about 80c/hour to heat
If your electricity costs 10c per kWh, that's 70c/hour to heat, that's a win
If your electricity fosts 15c per kWh, that's $1/hour to heat, that's a loss
If even you could, you may not want to. Instead one external heat pump handle heads on the top floor, which is generally bedrooms, and not occupied during the day; a second external unit to handle heads on the main floor, which are generally not occupied overnight.
Each individual smaller unit runs less because the load is more focused in 'zones'.
https://www.theecoexperts.co.uk/heat-pumps/high-temperature-...
Given that there are a lot of existing houses out there, surely drop in replacements should be more prevalent.
To be honest the prices I see out there are still generally 'luxury' anyway. If i am spending £20k on a boiler, then an extra £2k to have a secondary gas system that never/very rarely gets used wouldn't bother me at all.
What it can't do is both at the same time: make 70°C LWT when it's -28°C outside. It's designed for 65°C LWT (some models 60°C) and can only reach 70°C at a performance penalty (year-round) and can only maintain 70°C LWT down to -15°C and starts to lose max LWT, heating capacity, and even more efficiency below that. (Losing efficiency a few days out of the year is a minor concern. Not being able to meet the heat loss and heat transfer for the building for a few days is a much more serious issue for health and comfort.)
I guess being 2x as efficient (cheap) as electric resistive heating isn't super-terrible, but it's not great either.
Compare this to a favorable groundwater heat pump configuration with good radiators and insulation where the 'outside' (groundwater) is maybe 10°C and the target temp 30°C (close to room temp): (273+10)K/20K = ~14.
1. Your examples are heating up the inside air by using energy (burning fuel). Doing so will always be less than 100% efficient, some heating technologies are as little as 10-20% efficient (energy per kWh)
2. Heatpumps are instead using energy to do heat transfer. Moving heat from the outside to the inside.
The latter is way more efficient, with easily 300-400% efficiency. But obviously the colder it gets outside, the less heat is in the air to extract and the efficiency goes down.
Also, the $/fuel is different - if one system gets three times more joules from the same fuel, it doesn't mean it's more efficient as the other system may be using four times cheaper fuel; so a 300%-efficient heat pump is more efficient than a resistive heater but may be less efficient than a furnace burning cheap fuel.
Of course, you could throw more money at it. But it won't be cheap, and you won't see a return on your investment any time soon.
Leaky houses are already throwing money at the heating problem, and perhaps with a slower response time you would 'idle' the heating circuit at a passive 25C against 18C room temperature, and throttling up from there. Throwing money at it works!