Espar Airtronic M2 D4R
#11 in SplitFull review
For motorhomes and boats with long, branching duct runs that a standard 4 kW heater can not push through. Otherwise the D4L is cheaper and draws less power.
Amazon $1,849.99$1,849.99
The Espar Airtronic M2 D4R is the better diesel heater overall, rated 3.2 to 3.1. The Espar Airtronic M2 D4R leads on low setting. The Webasto Air Top Evo 40 wins on power draw. The Espar Airtronic M2 D4R costs $95.96 less ($1,849.99 vs $1,945.95).
Webasto Air Top Evo 40
#16 in SplitFull review
For 24V trucks and buses that need a type-approved 4 kW heater with automatic altitude adjustment. The high price buys Webasto build quality and approval, not more heat.
Amazon $1,945.95$1,945.95
Prices were last checked October 30, 2026 and are subject to change; the price and availability shown by the retailer at the time of purchase apply.
Which should you buy?
- Choose the Espar Airtronic M2 D4R for low setting (down to 0.9 kW vs down to 1.5 kW).
- Choose the Webasto Air Top Evo 40 for power draw (up to 55 W running vs up to 65 W running).
Scores side by side
Each factor is scored 0-100 against the same fixed reference points for every split diesel heater; a clear win is highlighted. How we rank explains each one.
| Factor weight | Espar Airtronic M2 D4R | Webasto Air Top Evo 40 |
|---|---|---|
| Overall rating | 3.2/5 | 3.1/5 |
| Value 25% | 8 $462 per kW ($1,849.99, 4 kW) | 7 $486 per kW ($1,945.95, 4 kW) |
| Type approval 20% | 100 type approved (ECE R122) | 100 type approved (ECE R122) |
| Controls and safety 15% | 65 holds a set temperature, automatic altitude, timer; no CO sensor | 65 holds a set temperature, automatic altitude; no CO sensor |
| Power draw 15% | 0 up to 65 W running | 11 up to 55 W running |
| Warranty 15% | 50 warranty not published (neutral score used) | 50 warranty not published (neutral score used) |
| Low setting 10% | 92 down to 0.9 kW | 42 down to 1.5 kW |
Specifications
| Espar Airtronic M2 D4R | Webasto Air Top Evo 40 | |
|---|---|---|
| Heating | ||
| Heat output (maker) | 4 kW | 4 kW |
| Lowest output | 0.9 kW | 1.5 kW |
| Fuel burn | 0.11 to 0.51 L/h | 0.18 to 0.49 L/h |
| Build | Split (installed) | Split (installed) |
| Power | ||
| Supply | 12V | 24V |
| Running draw | 6 to 65 W | 15 to 55 W |
| Starting draw | 100 W | - |
| Controls and safety | ||
| Thermostat | Yes | Yes |
| Automatic altitude | Yes, to 9,840 ft | Yes, to 7,220 ft |
| App | No | - |
| Timer | Yes | - |
| Remote | No | - |
| CO shutoff | No | No |
| Type approval | ECE R122 | ECE R122 |
| Build | ||
| Dimensions | 14.8 x 5.5 x 5.9 in | 16.7 x 5.8 x 6.4 in |
| Weight | 9.9 lb | 13 lb |
| Released | 2018-07 | 2014-10 |