4 ms·

I think what the post you replied to meant is that when your home needs a 10kW-20kW heater to actually be able to heat your home, then spending tons of money on

by Tor3 4y ago

I think what the post you replied to meant is that when your home needs a 10kW-20kW heater to actually be able to heat your home, then spending tons of money on a heat pump which (for the largest models) can maybe pump out 7kW of heat (equivalent) under optimal conditions (when it's not that cold outside) then you have paid a lot of money and you're still freezing. So you may as well install something else, even a simple wood stove can provide 10kW or more, sometimes much more.

blitzar 4y ago
If you need 20kW and you install a 7kW (equivalent) gas boiler you are in just as much trouble.
- iso1631 4y ago
  If you need 20kW and install a system that can output 20kW under the worst situation (resistive heating), you are probably averaging about 7kW of electric usage when the heating is on to generate 20kW (about 3:1 ratio on average) 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
- Tor3 4y ago
  Absolutely - but the important thing is that you can actually get a 20kW gas boiler, but you can't get a consumer 20kW heat pump. You can buy the most expensive consumer heat pump you can find, and it won't do at all if you actually need 20kW. So you can as well save the money as you'll have to install a gas heater (or oil or wood heater) anyway.
  - throw0101a 4y ago
    > Absolutely - but the important thing is that you can actually get a 20kW gas boiler, but you can't get a consumer 20kW heat pump. 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'.
leoedin 4y ago
The other issue is that a heat pump has to keep the output temperature relatively low to stay efficient - so just dropping a heat pump in to replace a wet heating system with a gas boiler will have two problems - the total power is less, and the amount of power the existing radiators can deliver to the room is too low. Effectively heating a house with lower temperature water needs big radiators or wet underfloor heating.
- blitzar 4y ago
  "The Daikin Altherma 3 H HT air source heat pump can provide water with temperatures up to 70°C – the same level as gas boilers – and can work when it’s as cold as -28°C outside." https://www.theecoexperts.co.uk/heat-pumps/high-temperature-air-source-heat-pumps 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.
  - Tor3 4y ago
    That article was generally informative, but they forgot (as far as I could tell after a quick read) to include something very important: How much heat can that Daikin heat pump provide? 3kW? 6kW? 10kW? Can it provide more than a standard air-to-air heat pump which typically can provide less than 7kW under optimal (read: Not that cold outside) conditions? This is important to know before buying one (any type of heat pump)
    - deleted 4y ago
      [deleted]
    - blitzar 4y ago
      "from £12,500" I guess it comes in different sizes 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.
  - sokoloff 4y ago

by Tor3 4y ago

blitzar 4y ago

If you need 20kW and you install a 7kW (equivalent) gas boiler you are in just as much trouble.

iso1631 4y ago
If you need 20kW and install a system that can output 20kW under the worst situation (resistive heating), you are probably averaging about 7kW of electric usage when the heating is on to generate 20kW (about 3:1 ratio on average) 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
Tor3 4y ago
Absolutely - but the important thing is that you can actually get a 20kW gas boiler, but you can't get a consumer 20kW heat pump. You can buy the most expensive consumer heat pump you can find, and it won't do at all if you actually need 20kW. So you can as well save the money as you'll have to install a gas heater (or oil or wood heater) anyway.
- throw0101a 4y ago
  > Absolutely - but the important thing is that you can actually get a 20kW gas boiler, but you can't get a consumer 20kW heat pump. 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'.

leoedin 4y ago

The other issue is that a heat pump has to keep the output temperature relatively low to stay efficient - so just dropping a heat pump in to replace a wet heating system with a gas boiler will have two problems - the total power is less, and the amount of power the existing radiators can deliver to the room is too low. Effectively heating a house with lower temperature water needs big radiators or wet underfloor heating.

blitzar 4y ago
"The Daikin Altherma 3 H HT air source heat pump can provide water with temperatures up to 70°C – the same level as gas boilers – and can work when it’s as cold as -28°C outside." https://www.theecoexperts.co.uk/heat-pumps/high-temperature-air-source-heat-pumps 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.
- Tor3 4y ago
  That article was generally informative, but they forgot (as far as I could tell after a quick read) to include something very important: How much heat can that Daikin heat pump provide? 3kW? 6kW? 10kW? Can it provide more than a standard air-to-air heat pump which typically can provide less than 7kW under optimal (read: Not that cold outside) conditions? This is important to know before buying one (any type of heat pump)
  - deleted 4y ago
    [deleted]
  - blitzar 4y ago
    "from £12,500" I guess it comes in different sizes 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.
- sokoloff 4y ago