A live view · for householders
What is the pipe outside your wall costing you?
If you have a heat pump, there is a run of pipe between the outdoor unit and your house. When that pipe is bare or thinly wrapped, it sheds heat into the garden all winter, and your heat pump quietly pays to replace it. Drag the slider and watch what the insulation choice is worth. The calculator runs entirely in your browser; nothing is sent anywhere unless you ask us for a reading below.
Insulating this run is worth
£18 a year
about £266 over fifteen years
One thing changes at a time; everything else holds still.
Left bare
£26 / year
314 kWh of lost heat
With 13 mm of insulation
£8 / year
97 kWh of lost heat
Your numbers
Your pipe, from above. The blue ring is the insulation you chose.
The first few millimetres do most of the work. After that, each one helps a little less.
The run the calculation does model, simulated in full
Your home has a second run: the hot water cylinder's primary circuit, the one the national calculation does model. Below, the same insulation choice on that run goes through the complete calculation, a full year, hour by hour, for a typical home. The simulation runs the heat pump itself, so no efficiency guess is needed, and it counts the circuit's real duty exactly.
On the primary circuit, the full simulation says this choice saves
£13 a year
52 kWh of electricity, at your rate, no efficiency assumption
On the outdoor run above, the formula says
£18 a year
with its flat 1,800-hour season and your efficiency setting
The two runs answer differently because their duties differ. The primary circuit works only while the cylinder charges, a few hundred hours a year, counted exactly by the simulation. The outdoor run sheds heat through the whole heating season, 2,098 simulated hours in this home, and the calculation never looks at it. A single formula answers a typical home; a reading answers yours.
nearest simulated thickness: 15 mm.
Precomputed from the full simulation; the simulation itself is verified between two independent implementations of the method within 1 kWh.
What the official calculation sees of this loss: nothing.
The run between your outdoor unit and the house sits on the emitter side, and the national calculation models no pipework loss there at all. Where pipework is in scope (the hot water cylinder's primary circuit), the insulation thickness is declared, never verified. Every pound on this page is invisible to the compliance figures your home is judged by. We implement the method; that is how we can say precisely where it looks away.
Get the reading for your home
This page shows one pipe, in general terms. The same record holds a reading for your home, from public data, before anyone visits. Leave a postcode and we will send it back.