Heat Pump Heat Loss Calculation & Flow Temperature – Why They Matter

What is a heat-loss calculation?

A heat-loss calculation estimates the heating power needed to maintain chosen indoor temperatures under specified cold outdoor conditions. Room-by-room results help the designer assess the heat pump and the emitters needed throughout the property.

• Whole-property heat-loss figure.
• Room-by-room results.
• Indoor design temperatures.
• Outdoor design temperature.
• Important insulation and ventilation assumptions.

What is flow temperature?

Flow temperature is the temperature of the water sent into the heating circuit. It is different from your room thermostat setting and should be distinguished from hot-water cylinder settings. Lower heating flow temperatures generally support better heat-pump efficiency, but the design must still provide enough heat to each room.

Why do radiators matter?

A radiator’s heat output depends partly on the water temperature passing through it. The installer should assess whether the emitters can meet each room’s heat requirement at the proposed design temperatures. Some may be suitable; others may need changes.

Why two quotes may propose different systems

A larger model number does not, by itself, establish a better design. Equipment output varies with operating conditions.

• Different building assumptions.
• Different indoor or outdoor design temperatures.
• Different emitter changes.
• Different flow temperatures.
• Different equipment performance at the stated conditions.

Five questions to send your installer

• Can you share the room-by-room heat-loss calculation?
• Which indoor and outdoor temperatures were used?
• What heating flow temperature has the system been designed around?
• Which emitters need changing, and why?
• What supports the selected heat pump’s output at those design conditions?

What a document check can establish

It can help you see whether these details are present, unclear or inconsistent across the documents. It cannot inspect the property, verify every calculation input or certify that the system is correctly designed.

Frequently asked questions

Is there one correct flow temperature for every home?

No. It depends on the building, emitters and system design. Ask for the reasoning behind the proposed temperature.

Is an EPC the same as a room-by-room heat-loss calculation?

No. Ask for the calculation used for the heating-system design.

Does a missing calculation prove the system is unsuitable?

No. It means you do not yet have that evidence in the documents supplied.

Should I change my heat-pump settings using this guide?

Use this guide to discuss the design with your installer. Operating settings should follow appropriate guidance for your installed system.