Question 1

Why does a heat pump need bigger radiators?

Accepted Answer

Because a heat pump produces water at a **much lower temperature** than a gas boiler, and a radiator's output depends heavily on how much hotter it is than the room.

**The temperature difference.** A gas boiler typically runs a flow temperature of 65–80°C. A heat pump is designed to run at **35–50°C**, and the lower it runs, the more efficiently it works.

**Why efficiency depends on it.** A heat pump does not create heat, it **moves** it from outside air or ground into the house. Its efficiency — the **coefficient of performance**, or the seasonal figure, **SCOP** — is the ratio of heat delivered to electricity consumed. The **smaller the temperature lift** the pump has to achieve, the higher that ratio. Pushing a heat pump to boiler temperatures is possible on many units and destroys the economics, since the running cost advantage over gas depends entirely on delivering several units of heat per unit of electricity.

**Why that means bigger radiators.** A radiator's heat output is a function of its surface area and the difference between the water temperature and the room temperature. Roughly halving that difference roughly halves the output — a radiator sized for 70°C water delivers a fraction of its rated output at 45°C. To put the same heat into the room at lower temperature, you need **more surface area**: physically larger radiators, or the same size with more panels and fins, or underfloor heating, which has an enormous surface area and is the ideal emitter for this reason.

**Not every radiator needs replacing.** A proper **room-by-room heat loss survey** frequently finds some radiators were already oversized and can stay. That survey is the single most important part of a heat pump installation, and skipping it is why poorly performing installations exist.

**Other things that change:** heat pumps work best running **continuously at low output** rather than in short bursts, so the old habit of two heating periods a day works against them; pipework may need upsizing; and **insulation improvements** reduce the required emitter size directly.

Question 2

What is the difference between a combi, system and conventional boiler?

Accepted Answer

They differ in how hot water is produced and stored, which determines what tanks you need and how the system behaves. Combi (combination) boiler. Heats water instantaneously on demand, directly from

Question 3

What does a thermostatic radiator valve do, and where should the thermostat go?

Accepted Answer

They control heat in different ways, and getting the relationship between them wrong is a common cause of a house that is simultaneously too hot and too cold. A thermostatic radiator valve (TRV)

Question 4

Why is one room in my house always colder than the others?

Accepted Answer

Because heat loss and heat delivery are not distributed evenly around a house, and one room is usually losing more, receiving less, or both. Working through the possibilities in order saves a lot of

Question 5

Why does my hot water run out so quickly?

Accepted Answer

The answer depends entirely on which kind of system you have, and the two common types fail in completely different ways. If you have a hot water cylinder, you have a fixed reservoir, and running out

Question 6

How do I work out what size radiator I need?

Accepted Answer

By calculating the heat loss of the room, then choosing a radiator whose output matches or slightly exceeds it. Radiator output is quoted in BTU per hour or watts (1 watt ≈ 3.41 BTU/h). What

Question 7

Do smart thermostats actually save money?

Accepted Answer

Sometimes, and considerably less than the marketing claims — the savings depend almost entirely on what you were doing before, and a household already heating efficiently has little left to gain.

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