How it's calculated
ΔT is the inside minus the outside temperature. The 1.15 factor allows for heat escaping through metal ribs and pillars, which are hard to insulate in a van. U-values are typical figures for each insulation level, including linings.
Worked example
A medium van, 3.0 × 1.7 × 1.4 m inside, with good insulation, 1.5 m² of single-glazed windows and 2 air changes an hour, kept at 20 °C when it's 0 °C outside, loses about 770 W. A 2 kW diesel heater has plenty in reserve for warming up quickly and for colder nights.
Where to improve
- Windows are often the biggest single loss in a van. Insulated covers make a large difference.
- Ventilation is essential for moisture and safety, so don't block vents. Insulate elsewhere.
- The insulation R-value calculator compares materials and thicknesses.
Frequently asked questions
What size heater do I need for a campervan?
Most panel vans and small campers lose 500–1,500 W in freezing weather, so a 2 kW diesel heater suits them. Large or poorly insulated vehicles may need 4–5 kW.
How many BTU to heat a small cabin?
A well-insulated 20 m² cabin might lose 1–2 kW (3,400–6,800 BTU/h) at 0 °C outside. Poorly insulated cabins can need two or three times that.