Most comparisons between heat pumps and gas boilers jump straight to a running cost table and stop there. That misses half the decision. The two systems behave differently in your house day to day, take different amounts of disruption to install, and suit different types of property, so this guide walks through the practical differences rather than just the numbers.
If you want the fuel cost comparison specifically, that is covered elsewhere; here we are focused on comfort, control, hot water, space, noise and longevity, the things that actually shape whether you are happy with the choice five years on.
Comfort and control
A gas boiler heats water quickly to a high temperature and cycles on and off to hold a room at target temperature. A heat pump generally runs for longer periods at a lower, steadier flow temperature, often 35 to 55C rather than 70C plus, which tends to produce a more even background warmth rather than short bursts of intense heat.
Some homeowners love the steadier feel, others miss the quick blast of heat a boiler gives on a cold morning. It is a genuine lifestyle difference, not just a technical one.
Flow temperature and your radiators
This is the biggest practical knock-on effect. Because heat pumps work best at lower flow temperatures, radiators sized for a hot gas boiler system are often too small to heat the room adequately at the lower temperature a heat pump prefers. Expect some radiators to need upsizing as part of a heat pump conversion. A straight gas boiler swap, by contrast, rarely needs any radiator changes at all.
Hot water: cylinder versus combi
Most heat pump installations need a hot water cylinder, generally somewhere in the range of 150 to 300 litres depending on household size, because the heat pump cannot produce the instant, high flow rate hot water a combi boiler does. If your home currently runs a combi with no cylinder and no space for one, that space has to come from somewhere, often an airing cupboard or loft conversion of some kind.
Space and noise
A heat pump needs external space for the outdoor unit, generally on a wall bracket or ground base with clearance for airflow, plus internal space for the cylinder. A gas boiler needs a wall mounted internal space only, no external unit and no cylinder if it is a combi. On noise, heat pumps run at a low but constant hum when operating, worth considering for siting near bedroom windows; gas boilers are essentially silent except during ignition.
Installation disruption
A like for like gas boiler swap is typically a one to two day job. A heat pump conversion involves more: siting and fitting the outdoor unit, running new pipework, installing or relocating a cylinder, upgrading radiators, and commissioning the controls, which usually means several days of work and more disruption around the house.
Longevity and fuel availability
Both systems have broadly similar expected lifespans when properly maintained, though this varies by manufacturer and usage. The bigger long term factor for many Borders and East Lothian homes is fuel availability: if you are off the gas grid on oil or LPG, a heat pump removes reliance on fuel deliveries and storage tanks, which some homeowners value regardless of the running cost comparison.
Side by side summary
| Factor | Gas boiler | Heat pump |
|---|---|---|
| Typical flow temperature | Up to 70C plus | 35 to 55C |
| Hot water delivery | Instant with a combi | Via cylinder, slower recovery |
| Install time for a straight swap | 1 to 2 days | Several days, often with radiator work |
| External space needed | None | Yes, for the outdoor unit |
| Off gas grid suitability | Needs oil or LPG supply | Runs on electricity only |
| Noise in operation | Effectively silent | Low constant hum when running |
Frequently asked questions
- Is switching from gas to a heat pump always more disruptive than a boiler swap?
- Generally yes, because it usually involves a cylinder, some radiator upgrades and an outdoor unit, none of which a like for like gas boiler swap needs.
- Can I keep my combi boiler style instant hot water with a heat pump?
- Not in the same way. Heat pumps are paired with a cylinder rather than delivering instant high flow rate hot water, so households used to combi convenience should factor this in.
- Which is quieter, day to day?
- A gas boiler is essentially silent in normal use. A heat pump has a low constant hum from the outdoor unit while running, which is worth considering for siting.
- Does off grid change the decision?
- It often does. Homes on oil or LPG frequently find the comparison against a heat pump more favourable than homes already on mains gas.
- Do I have to decide on price alone?
- No, and we would not recommend it. Comfort style, hot water needs, available space and how long you plan to stay in the house all matter alongside cost.
Not sure which route suits your house
Talk it through with us and we will help you weigh up a heat pump conversion against a straight boiler replacement.