Pipe Heat Loss Calculator
Calculate heat loss from uninsulated hot water pipes.
Find annual energy waste and payback period for adding foam or fiberglass pipe insulation.
Hot water pipes in unconditioned spaces (basements, crawl spaces, attics) radiate heat to the surrounding air continuously. This costs money even when no one is using hot water — the water heater cycles on to maintain tank temperature because heat is leaking out through the pipes.
The heat loss formula
For an uninsulated pipe, heat loss per meter per hour is:
Q = U x pi x D x L x (T_water - T_ambient)
Where U is the convective heat transfer coefficient (approximately 10 W/m2K for a still-air environment), D is the outer pipe diameter in meters, L is length in meters, and the temperature difference is in Kelvin (same as Celsius difference).
Simplified for common pipe sizes:
- 15mm (1/2 in) copper at 60C in a 15C space: ~9 W/m
- 22mm (3/4 in) at same conditions: ~13 W/m
- 35mm (1.25 in) at same conditions: ~20 W/m
Insulation reduces heat loss by 70-80% for standard foam pipe lagging. Fiberglass wrap achieves 85-90% reduction.
Payback period
Insulating pipes typically costs $1-3 per meter (foam lagging). At electricity or gas rates of $0.10-0.15/kWh, a typical installation pays back in 3-18 months in unconditioned spaces.
In conditioned spaces (inside the heated home), uninsulated pipes actually contribute heat to the room — not wasted energy in winter, but wasted energy in summer when the AC must remove that heat. Year-round savings are smaller in climate-controlled spaces.