MCS 031 heat pump performance estimates: what the document requires and why getting it wrong costs you jobs

A customer rings eighteen months after commissioning. Their bill looks nothing like the figure on your quote, and they've kept the paperwork. Or it's an auditor asking to see the estimate and the EPC behind it. Either way the question is the same: what did you base this on, and can you show it?

MCS 031 is what makes that a short conversation. A heat pump performance estimate is one of the heat pump quote requirements under MCS - it goes to the customer at quoting stage, and a copy is retained for audit. Four inputs decide what it says.

The four inputs that decide the number

The EPC. Space heating demand, hot water demand and total property floorspace all come off a valid Energy Performance Certificate. Valid means not expired, and not overtaken by an extension or refurbishment that changes the demand. The mistake that keeps appearing: floorspace is not footprint. Enter the footprint of a two-story house and your watts per square metre jumps, dropping the property into a worse heat loss band and pulling the estimate with it.

The postcode. Degree days and the outdoor low temperature come from a lookup table by postcode prefix. The spread is wider than people assume - 1,800 degree days at the mild end, 2,668 at the cold end - and it feeds straight into the specific heat loss. Use the office postcode rather than the property's and everything downstream is quietly wrong.

The emitters and the flow temperature. Four options: existing radiators, mostly upgraded radiators, mostly underfloor, or roughly half and half. Then the flow temperature: and here's the bit worth knowing. Where existing radiators are staying, the standard sets 60°C as the default, and you can only go below it if a room-by-room heat loss calculation justifies the lower figure. Putting 45°C on an estimate because the unit is capable of it, on a house nobody has surveyed room by room, is the most common way a quote stops matching the standard. It also flatters the SPF, which is why it gets noticed.

The hot water side. Hot water runs at a fixed performance factor of 1.7 whatever pump you fit. What you control is pasteurisation: cylinder volume and how often the immersion runs - daily, weekly, or not at all where the heat pump handles it. Setting that to zero on a system that can't reach pasteurisation temperature quietly removes a real load.

Why the unit's SCOP doesn't move the answer

The old SCOP calculation route, take the seasonal coefficient of performance from the product data and work back to an SPF, is no longer how MCS 031 works. The current version reads the SPF straight from a heat emitter guide lookup: heat loss band, flow temperature, air or ground source. Specify a more efficient unit and the estimate doesn't move.

That doesn't make the SCOP irrelevant on site, equipment selection still affects real system efficiency. It just means the estimate isn't where you sell it.

What a clean one looks like

The standard's own worked example: a Welsh property, 145 m², 15,500 kWh of space heating and 2,900 kWh of hot water from the EPC, upgraded radiators at 50°C, air source. That gives 59 W/m², an SPF of 3.1 and about 6,800 kWh a year - presented as a range of 6,100 to 7,500.

The range matters. Output is deliberately given at plus or minus 10%, and the standard's own key information says a real-world spread of 25 to 30% wouldn't be unreasonable once occupancy, hot water habits and open windows are involved. Performance estimate accuracy has stated limits, and saying so up front is stronger than a confident single figure you'll be held to.

The running cost figure is yours, not the standard's

MCS 031 gives kilowatt hours, not pounds. Most installers convert them for the customer anyway: fair enough, it's the question every homeowner is really asking. Just be clear whose number is whose: the kWh came from the standard, the tariff is your assumption, so put the rate and the date beside it. When that customer calls about their bill, you want to be discussing what electricity cost, not whether you overpromised.

Why the file is what protects you

The estimate must be kept for the period set out in MCS 001 and produced on request, so treat it as MCS documentation, not a sales sheet. Keep the EPC reference and its date, the emitter option and flow temperature you selected, the room-by-room heat loss if that's what justified going below 60°C, and your cylinder and pasteurisation assumptions.

That's the entire defence: every figure traceable to a document or a stated choice. The wider compliance picture runs on the same discipline - the permitted development rules now work that way too, a calculation on file or nothing.

It matters more from here, not less. As the Future Homes Standard pushes heat pumps into the mainstream of new build, estimates will be compared side by side far more often, and the ones that hold up will have workings behind them.

If your performance estimates live in a spreadsheet separate from the heat loss and design they depend on, that's where errors get in.

Book a demo today and we'll show you the estimate built from the same data as the rest of the job.