Replacing a gas combination boiler with a heat pump

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This is not easy!

A small gas boiler starts about 20kW and can provide water at 55 degrees or higher. More powerful system boilers are not much bigger than the smallest wall-hung unit. A small heat pump is 3kW. A 20kW heat pump is BIG. They scale up in size as they get more powerful. Also, it's best if they are outside the living space to get their source of energy.

In a small house, bungalow or flat, a 20kW gas combi is more than adequate, so fitting one is sure to satisfy demand, especially if the house has a water tank and a bath.

Designing a system to replace it with a heat pump needs a lot more knowlege and care. Heat pumps are smaller and work at lower temperatures. You have to consider insulation, solar gain, drafts, room size and whether the water tank or the bath are still needed by the occupants. Instant showers are now common and washing machines heat their own water, for example. Also there are several types of heat pump, extracting heat from different sources.

See also Heat Pumps

Some examples

Much of the advice on Central heating design is still relevent, but the lower temperatures might dictate a new strategy rather than just adjusting radiator sizes.

System Design Considerations

  • Are bedrooms much smaller than the living area? Perhaps you need two separate systems!
  • Do you use the bath? Perhaps an instant shower would suit.
  • Do you have and still use a hot water cylinder? Perhaps localised instant water heating would be better.
  • Do you have a garden, a balcony or a greenhouse? You have much greater options for fitting a heat pump.
  • Do you have single-panel radiators? You can double the radiation source easily.

Changing to heat pumps will always mean having good insulation first, walls, roof and floors too if possible. Get those done before you even think about making the change

DIY Activity

Much of the work can be a DIY project. If using a Monobloc unit, all of it can be DIY really. Don't be bullied into taking a package sponsored by the big energy companies or Government. You don't need to retire the gas boiler until the new system is in place so the work can be done at a leisurely pace. Pipes, cables, drill a few holes, get a greenhouse or conservatory if you feel like it. See also Talk:Heat Pumps