Smart controls and heat pumps

Boilers and heat pumps want opposite things

A gas boiler is happy being driven by a simple thermostat: heat hard until the room hits target, switch off, repeat. A heat pump is the opposite. It is most efficient running a low, steady flow temperature over long periods. Switching it hard on and off — "short cycling" — drags its efficiency down and wears it out.

Weather compensation is the point

Weather compensation adjusts the flow temperature gradually against the outdoor temperature: cooler water when it's mild, warmer when it's cold, always aiming for the lowest temperature that keeps you comfortable. That's where a heat pump's efficiency lives. A smart thermostat that overrides weather compensation to do simple on/off control can undo it — the home stays warm, but the running cost climbs.

Protecting the COP

A heat pump's COP (coefficient of performance) — the heat out per unit of electricity in — falls as flow temperature rises. The right control keeps flow temperatures low and avoids short cycling, protecting the COP. It doesn't create efficiency; it stops you throwing efficiency away. This is exactly why the choice of control isn't cosmetic on a heat pump.

What to actually do

• Take the installer's control. For a Boiler Upgrade Scheme installation, your MCS installer selects compatible controls as part of the job — that's the safe default.
• If you're adding smart control later, check heat-pump compatibility specifically. Some smart thermostats (Tado among them) support weather compensation or work alongside it better than others — see best smart thermostats.
• Don't retrofit a boiler-style thermostat to a heat pump on the assumption that all thermostats are interchangeable. They aren't.