Common Heat Pump Retrofit Mistakes to Avoid

Mistake 1: Skipping the fabric

Fitting a heat pump to a leaky, under-insulated home forces it to run at a high flow temperature, which collapses its efficiency. The fabric work is often skipped because it sits outside the heat-pump quote — but it is the single biggest factor in how the system performs. Fabric first, plant last.

Mistake 2: Oversizing the unit

Sizing from floor area, a rule of thumb, or an EPC — then adding a 'safety margin' — produces an oversized heat pump that short-cycles and runs inefficiently. A measured, room-by-room heat-loss calculation prevents this.

Mistake 3: Ignoring airtightness

Draughts add directly to the heat demand and chill rooms at floor level. Because air leakage is invisible, it is routinely underestimated and the heat pump is sized to cover losses that could have been cheaply sealed. A blower door test quantifies it.

Mistake 4: Leaving emitters undersized

Existing radiators sized for a 70°C boiler often cannot deliver enough heat at 45°C, so the installer raises the flow temperature to compensate — and the efficiency falls. Checking and upsizing emitters room by room keeps the flow temperature, and the bills, low.

Mistake 5: Tightening without ventilating

Insulating and air-sealing for readiness makes the home tighter. Without a matching ventilation upgrade, indoor humidity rises and condensation and mould follow. Build tight, ventilate right.

Mistake 6: Running it like a boiler

Heat pumps are designed to run long and gentle at a low, weather-compensated flow temperature — not to be switched on and off for short bursts at high temperature. Setting the controls like a boiler is a common cause of poor real-world efficiency.

How RetrofitIQ helps you avoid them

Measured heat-loss survey to size the system correctly
Thermal imaging and a blower door test to target fabric and airtightness improvements
Emitter review for low-temperature operation in every room
A ventilation strategy matched to the tightened fabric
An independent readiness report for your installer — and verification afterwards

Common questions from clients.

Who is responsible for getting the fabric right — me or the installer?

Fabric improvements usually sit outside an MCS heat-pump installation, which is why they get missed. An independent readiness assessment bridges that gap, telling you what fabric and emitter work to do before the installer designs the system.

Is oversizing really a problem?

Yes. Oversized heat pumps short-cycle, run less efficiently, wear faster and cost more to buy. Accurate, measured sizing avoids it and usually reduces the capital cost too.

Can you work with my chosen installer?

Yes. We provide the independent readiness, heat-loss and emitter evidence; your MCS installer designs and fits the system. The two roles complement each other and give you a system designed on measured data.

How do I know if my quote is any good?

Look for a room-by-room heat-loss calculation, a stated design flow temperature (ideally 45°C or below), an emitter schedule, weather compensation, and a justification for any buffer tank. We can review a quote against your readiness assessment.

What's the most expensive mistake to fix later?

An oversized unit and undersized emitters, because both are hard to change after installation. Getting the sizing and emitters right before the work is far cheaper than retrofitting corrections.

Common heat pump retrofit mistakes — and how to avoid them.