# Is insulating your hot water pipes worth it?

> Enter your pipe, your insulation and your energy price. Get the yearly saving, the payback time and a straight answer.

[View the web page](https://heatuneed.com/pipe-insulation-calculator/)

## Bare pipes leak heat every hour they are hot

An uninsulated hot water pipe in an unheated basement loses roughly 30 to 50 watts per metre, around the clock. This calculator estimates that loss, compares it against the same pipe with insulation, and tells you whether the insulation pays for itself.

## How the calculation works

The tool models the pipe as a cylinder losing heat by conduction through the insulation, then by convection and radiation from the outer surface.

1. **Insulation resistance** — The insulation shell resists heat with ln(D_outer / D_pipe) / (2 pi k), where k is the material conductivity. Doubling the thickness does not halve the loss - the returns taper off.
2. **Surface film** — The outer surface loses heat by natural convection and radiation. The tool solves for the surface temperature iteratively rather than assuming a fixed film coefficient.
3. **Annual energy** — Heat loss in watts is multiplied by your running hours, then divided by the efficiency or COP of your heat source to get the fuel or electricity you actually buy.
4. **Payback** — Installed cost divided by yearly money saved. Anything under about three years is an easy decision.


## What the calculator asks for

### Pipe sizes offered

- Copper 15 mm (1/2") — wall 1 mm
- Copper 18 mm — wall 1 mm
- Copper 22 mm (3/4") — wall 1 mm
- Copper 28 mm (1") — wall 1.2 mm
- Steel DN15 - 1/2" (21.3 mm) — wall 2.6 mm
- Steel DN20 - 3/4" (26.9 mm) — wall 2.6 mm
- Steel DN25 - 1" (33.7 mm) — wall 3.2 mm
- Steel DN32 - 1 1/4" (42.4 mm) — wall 3.2 mm
- Steel DN40 - 1 1/2" (48.3 mm) — wall 3.2 mm
- Steel DN50 - 2" (60.3 mm) — wall 3.6 mm
- Multilayer (PEX-AL-PEX) 16 x 2 mm — wall 2 mm
- Multilayer (PEX-AL-PEX) 20 x 2 mm — wall 2 mm
- Multilayer (PEX-AL-PEX) 26 x 3 mm — wall 3 mm
- Multilayer (PEX-AL-PEX) 32 x 3 mm — wall 3 mm
- Multilayer (PEX-AL-PEX) 40 x 3.5 mm — wall 3.5 mm
- Multilayer (PEX-AL-PEX) 50 x 4 mm — wall 4 mm


### Where the pipe runs

Heat escaping into a heated room is partly useful, so only 45 percent of that loss is counted as a saving. In an unheated space or outdoors the whole loss counts.

- Unheated space (basement, garage, crawl space)
- Heated room
- Outdoors or unheated shaft


### Insulation materials and conductivity

- Elastomeric foam (Armaflex type) — 0.038 W/mK
- Polyethylene foam sleeve — 0.04 W/mK
- Mineral / rock wool shell — 0.04 W/mK
- Glass wool shell — 0.035 W/mK
- PIR / PUR rigid foam — 0.026 W/mK
- Phenolic foam — 0.022 W/mK


### Insulation thicknesses offered

9 mm, 13 mm, 19 mm, 25 mm, 32 mm, 40 mm, 50 mm

### Heat sources, default efficiency, energy price and CO2 factor

- Condensing gas boiler — Efficiency / COP 0.92, Energy price per kWh 0.06 USD, CO2 0.202 kg/kWh
- Older gas boiler — Efficiency / COP 0.75, Energy price per kWh 0.06 USD, CO2 0.202 kg/kWh
- Oil boiler — Efficiency / COP 0.85, Energy price per kWh 0.11 USD, CO2 0.267 kg/kWh
- Heat pump (COP 3.5) — Efficiency / COP 3.5, Energy price per kWh 0.17 USD, CO2 0.37 kg/kWh
- Electric water heater — Efficiency / COP 1.0, Energy price per kWh 0.17 USD, CO2 0.37 kg/kWh
- District heating — Efficiency / COP 1.0, Energy price per kWh 0.1 USD, CO2 0.11 kg/kWh


Currency: USD, EUR. Only the currency the figures are shown in changes. The prices stay exactly as you typed them, so set them to what you actually pay.

### The two operating modes

A pipe held permanently hot and a pipe that only warms up after a tap is opened are different problems, so the calculator models them separately. Pipe material conductivity: copper 380, steel 50, multilayer 0.43 W/mK.

- Circulation loop — the pump keeps it hot — Hours hot per day, Days hot per year
- Only hot just after a tap is opened — Draw-offs per day, Typical gap between draw-offs

On a pipe without a loop the energy wasted per draw-off is the heat stored in the water and the pipe wall. Insulation slows the cool-down rather than preventing it, so it only saves energy when the next draw-off arrives while the pipe is still warm.

### How the water cools

Estimated water temperature after each interval. The highlighted row is your typical gap between draw-offs; 40 °C is treated as still usable at the tap.

## Your result

### How the verdict is decided

The verdict follows the simple payback time: under 3 years is a strong yes, 3 to 7 years is worth doing, 7 to 15 years is borderline, and over 15 years does not pay back on cost alone.

- **Insulate it — this pays back fast** — The insulation pays for itself in well under three years, then keeps saving for decades.
- **Worth insulating** — A payback in this range is normal for pipe insulation and comfortably beats leaving the pipe bare.
- **Borderline — insulate if the wall is already open** — The saving is real but slow to repay. Do it while you have access, or pick a cheaper sleeve.
- **Not worth it on cost alone** — At this price and running time the insulation will not repay itself in a reasonable period.
- **Nothing to save here** — With these inputs the pipe loses almost nothing, so there is no meaningful saving to capture.

This pipe runs through a heated room, so part of the lost heat still warms the house. Only the wasted share is counted as a saving.

Estimates based on steady-state cylindrical heat transfer with natural convection and radiation at the surface. Real installations vary with air movement, fittings, valves, supports and insulation quality.

## Common questions


### How much does pipe insulation actually save?

A 15 metre uninsulated 22 mm loop at 60 °C in a 12 °C basement loses close to 50 W per metre, which is around 6,000 kWh of heat a year if it runs continuously. A 19 mm sleeve cuts that by roughly 80 percent. The material costs well under 150 and the saving is normally recovered in the first year.

### What thickness should I use?

For domestic hot water and heating pipes indoors, 13 to 25 mm covers most cases. Going thicker keeps helping but with diminishing returns, so the standard rule of matching insulation thickness to pipe diameter is a good default.

### Is it worth insulating pipes inside heated rooms?

Less so in winter, because the escaped heat warms the room anyway. It still pays for domestic hot water loops that run all summer, and it keeps the water hotter at the tap.

### Do I need to insulate valves and fittings too?

Yes. An uninsulated valve or flange can lose as much heat as one to two metres of bare pipe, so leaving them out undoes a noticeable part of the saving.

### Does insulation help cold water pipes?

It does, for a different reason: it prevents condensation and slows freezing. Those savings are not energy savings, so this calculator does not model them.


## Want the same analysis for a whole room?

Heatuneed scans your rooms with LiDAR and calculates heat loss through walls, windows, doors and roofs the same way this tool handles pipes.

- [Check app availability](https://heatuneed.com/app-store/)