Every diesel heater gets a score from 0 to 100% built from six factors, which maps onto the 5-point rating shown on the site (a 0% score would be 1.5 stars; a perfect score, 5). Each factor is scored against fixed reference points, not against the other products in the list, so adding a new model never moves another model’s rating. Heaters are grouped by build, split or all in one, and each group has its own price scale.
| Factor | Measures | Weight |
|---|---|---|
| Value | price per credible kilowatt | 25% |
| Type approval | ECE R122 approval for vehicle heaters | 20% |
| Controls and safety | thermostat, CO shutoff, altitude, app, timer | 15% |
| Power draw | battery drain while running | 15% |
| Warranty | warranty length | 15% |
| Low setting | how gently it can run in a small space | 10% |
Where the numbers come from
Heat output, fuel burn, power draw, controls and warranty come from the maker’s product page, manual or warranty page. Type approval comes from the maker’s documentation. Heat output, noise and power draw measured by independent testers are shown on product pages where they’ve been published.
Checking the heat rating
Diesel holds about 10 kWh of energy per liter. A heater burning 0.6 liters an hour at full power therefore has about 6 kW of fuel energy going in, and can’t put out more than that as heat. Type-approved heaters, which are tested, turn about 8 kW of heat out of each liter per hour they burn: a Webasto Air Top 2000 STC gives 2 kW from 0.24 L/h, an Espar Airtronic D4 4 kW from 0.51 L/h.
So when a heater’s rated output is more than 10 kW for each liter per hour of its own maximum fuel burn, we score it on its fuel burn times 8 instead, and the product page shows both: “8 kW claimed (about 5 kW from its fuel burn)”. When a heater gives a rating but no fuel figure and no type approval, there’s nothing to check it against, so its value factor gets the neutral middle score, marked estimated.
The factors
Value is the current price divided by the credible heat output, on a log scale for each group, so going from $50 to $25 a kilowatt counts as much as going from $600 to $300.
| Group | Scores 0 | Full marks |
|---|---|---|
| Split | $600 per kW | $25 per kW |
| All in one | $300 per kW | $20 per kW |
Type approval is full marks for a heater approved to UN ECE R122, the safety standard for heating systems in vehicles, and zero otherwise. Approval means a lab has tested how the heater handles overheating, flame out, exhaust leaks and fuel leaks. A CE mark alone doesn’t count, since makers declare it themselves.
Controls and safety adds up the features that make a heater safe and easy to live with:
| Feature | Share of the factor |
|---|---|
| Holds a set room temperature on its own | 30% |
| Built-in carbon monoxide sensor that shuts it off | 20% |
| Adjusts its fuel for altitude by itself | 20% |
| Phone app | 15% |
| Timer start | 15% |
A heater that only runs at fixed levels cycles between too hot and too cold. Without altitude adjustment, most heaters soot up and run rich above about 5,000 ft. A feature the maker doesn’t state either way gets half credit.
Power draw is the maker’s highest running draw, which decides how long a heater can run overnight from a battery: 60 W scores zero and 15 W full marks. The brief draw while the glow plug lights it is listed but not scored.
Warranty: 1 year scores zero and 3 years full marks.
Low setting is the lowest heat output, which decides whether a heater can run gently all night in a small van or tent instead of switching on and off. 2 kW scores zero and 0.8 kW full marks. When the maker gives only a minimum fuel burn, it’s multiplied by 8 as above and marked estimated.
What isn’t scored
Noise, tank size, voltage options, remotes, size and weight are listed but not scored. Independent tests are listed where they exist, but there are too few to score.
Missing data
If a figure isn’t published, that factor gets the neutral middle score (50) and the product page marks it as estimated.
Ties and discontinued models
Products are ranked by score within each group. Discontinued models stay listed but rank below every current model and can be hidden with the “Hide discontinued” filter.