Heat Pump Installation Mistakes to Avoid

An oversized heat pump can waste £200-£400 per year in unnecessary electricity. A poorly insulated home can double your running costs. And choosing the cheapest installer over the most competent one is the single most expensive mistake homeowners make — here are the pitfalls to avoid and how to get it right.

Most heat pump problems are not caused by the technology itself — they are caused by installation mistakes. A correctly designed and installed heat pump will deliver excellent performance for 15 to 20 years. Here are the most common mistakes and how to avoid them.

Mistake 1: Wrong Sizing

The most common and costly mistake. An oversized heat pump short-cycles, reducing efficiency and increasing wear. An undersized one cannot keep you warm. The solution is a proper room-by-room heat loss calculation — never let an installer size your system based on floor area alone or by matching your existing boiler size.

Mistake 2: Skipping the Proper Survey

A thorough heat pump survey takes 1.5 to 3 hours. If an installer offers a quote after a 30-minute visit or without visiting at all, they are cutting corners. MCS requires a physical survey and measured heat loss calculation.

Mistake 3: Ignoring Insulation

Installing a heat pump in a poorly insulated home means higher running costs and possibly needing a larger, more expensive system. Preparing your home with basic insulation improvements first is the smarter approach.

Mistake 4: Not Assessing Radiators

Heat pumps run at lower flow temperatures than boilers. Some radiators may need upgrading to deliver enough heat at these temperatures. Failing to check this results in rooms that never get warm enough.

Mistake 5: Choosing the Cheapest Installer

The cheapest quote is often the one that cut the most corners. Compare at least three MCS-certified installers and look at the quality of the survey, the detail in the heat loss calculation, and the installer's track record.

Mistake 6: Setting Flow Temperatures Too High

Running a heat pump at 55°C flow temperature to make radiators feel "boiler hot" destroys efficiency. The system should run at the lowest flow temperature that keeps the house comfortable — typically 35 to 45°C. This is why correct radiator sizing and weather compensation settings matter.

Mistake 7: Poor Outdoor Unit Positioning

Cramming the outdoor unit into a tight corner restricts airflow (reducing efficiency), amplifies noise off nearby walls, and makes future servicing difficult.

Combining a heat pump with solar panels can further improve the economics, but only if the heat pump itself is correctly sized and installed first. Get the fundamentals right and the savings follow naturally.

Frequently Asked Questions

What is the most common heat pump installation mistake?

Incorrect sizing. This stems from skipping a proper room-by-room heat loss calculation and is the biggest cause of poor performance.

How do I avoid choosing a bad installer?

Only use MCS-certified installers, get at least three quotes, insist on a detailed survey and heat loss calculation, and check reviews.

Can installation mistakes be fixed afterwards?

Some can — flow temperatures and weather compensation can be adjusted, and radiators upgraded. But fundamental sizing errors may require replacing the unit entirely.