How each one heats the house
A gas boiler burns gas to heat water to around 60 to 70 degrees and pumps it round the radiators. It heats up fast, so the heating can be off all day and on for an hour in the evening.
A heat pump takes heat from the outside air, even on a cold day, and uses electricity to raise it to a useful temperature. It works best sending water round at 35 to 50 degrees, so the radiators feel warm rather than hot, and the house is kept at a steady temperature rather than heated in bursts.
For every unit of electricity a heat pump uses it delivers roughly three units of heat. A gas boiler delivers a little under one unit of heat for each unit of gas. Whether that saves money depends on the price of electricity against gas, and on the house.
Which houses suit a heat pump
- InsulationA heat pump can only supply so much heat. A house that leaks it faster than that never gets warm. Loft insulation, cavity or solid wall insulation and draught-proofing come first.
- RadiatorsBecause the water is cooler, most radiators need to be bigger. In some houses that means changing most of them, or fitting underfloor heating.
- A hot water cylinderA heat pump can't make hot water on demand like a combi. A cylinder is needed, and space for it.
- Room outsideThe outdoor unit needs a wall or a base with clear air around it, and it hums when running. Terraces with no side access are harder.
- Electricity supplyThe house's supply has to have the capacity. Most do; some older ones need upgrading.
A well insulated house built in the last twenty years, or an older one that has been insulated, usually suits a heat pump. A draughty solid-walled Victorian terrace with small radiators and a combi usually doesn't, yet.
When a new gas boiler is the right answer
If the boiler has failed in January and the house needs heat this week, a like for like gas boiler is fitted in a day and works with the radiators you have. If the house is poorly insulated and you can't insulate it yet, a boiler will heat it and a heat pump will struggle. If there is nowhere for a cylinder, a combi is the only option that makes hot water on demand.
A modern condensing boiler is far more efficient than one fitted twenty years ago, so replacing an old boiler cuts the gas bill on its own. What a new boiler costs.
How to decide
Insulate first
Whatever you fit, a house that holds its heat costs less to run. Do the loft and the draughts before the heating.
Get a heat loss survey
This tells you how much heat the house needs and whether a heat pump can supply it with the radiators you have.
Price both
The fitting cost, the running cost and, for a heat pump, the radiator changes and the cylinder. Ian will give you the boiler price and a heat pump price side by side.
Decide with the timescale
A boiler that has died wants replacing this week. A heat pump is a planned job for spring or summer.
Questions
Do you fit air source heat pumps?
Yes, installed and serviced. Ian will tell you whether one suits your house before you decide, because a heat pump wants bigger radiators and a well insulated house to work well. Heat pumps.
Does air conditioning heat as well?
Yes. Nearly every unit fitted today is a heat pump, so the same system heats the room in winter and cools it in summer.
How long should a boiler last?
A well serviced gas boiler is commonly expected to last 10 to 15 years. Once repairs start costing a large share of a new boiler, or parts are no longer made for it, replacing it is usually the better spend.