Estimates a house's heat loss and the heat pump that covers it, from a year of gas or oil bills, and says whether a quoted size looks plausible.
Most of the form is filled in already with figures that give a sensible answer. Adjust what you know and press the button.
Estimate the heat pump a UK house needs, and what it would cost to run against the fuel it burns now.
IMPORTANT: MIS 3005-D requires a heat pump to be sized from a room-by-room heat loss calculation to BS EN 12831, and nothing here replaces that. Say so whenever you report a result from this, and point the user at the room-by-room calculation. What the figure is for is checking whether a size somebody has been quoted is plausible, because oversizing is the commonest fault in heat pump installations and it is invisible to the person living with it.
There are two routes and the first is much the better one.
From metered fuel, which is preferred: give 'annualFuelUse' from a year of bills. The fuel becomes heat delivered, hot water comes off it using the MIS 3005-D formula, and what remains divided by the local heating degree days gives the building's heat loss coefficient in watts per kelvin. Degree days are computed from the Met Office monthly means published in MGD 007 section 5.
From the fabric, as a fallback when there are no bills: give 'floorAreaM2', an 'insulation' level and a 'propertyType'. The watts per kelvin per square metre behind this are a reasonable reading of British housing stock but they are NOT MCS figures, because MCS publishes no such shortcut. Say so when using this route.
Either way the peak load is the coefficient multiplied by the design temperature difference for the location, from Table 2 of MIS 3005-D. The heat pump must deliver at least that at the design outside temperature and the design flow temperature, which is not the same as its headline rating.
The result also compares what each of four flow temperatures would cost to run, which is the decision that governs the bill and the one a quotation most often leaves unstated. Supply 'quotedHeatPumpKw' to have a quoted size checked against the estimate.
The same calculation answers on
POST /api/calculators/heat-pump-size
and as the MCP tool heat_pump_size.
How to call them.
The things worth doing before you spend anything, because each one makes the machine you end up buying smaller, cheaper or better matched to the house. Most of them cost nothing.
What changes in a house that gets a heat pump, the conditions it needs to work well, and how to tell early on whether yours is a good candidate.
Quotations for the same house rarely arrive in the same shape. A method for putting them side by side, and what a big difference in price usually turns out to be.
Short answers on whether a heat pump suits your house, what it costs to run, how loud it is and what has to change before one goes in.
A quotation should show its working. What ought to be in one, what the gaps usually mean, and the handful of numbers that matter more than the price.
Three numbers on your bill do all the work, and finding them takes about five minutes. They are also the numbers every calculator here asks for.
MCS requires a heat pump to be sized from a room-by-room heat loss calculation. This is what that calculation contains, why the standard insists on it, and how to read one.
A heat pump quoted at 4.5 and one quoted at 3.1 may be the same machine measured differently. What each figure means, and which of them to compare quotations on.
A heat pump moves heat instead of making it, which is why it can deliver more heat than the electricity it consumes. What that means for your radiators and for the way the house is heated.
A heat pump quotation should come with a room-by-room heat loss calculation. Here is what its columns mean and the handful of checks that catch most errors.