Increasing the effective altitude of a Webasto heater

There are no HAK (high altitude kits) available for Webasto and Espar heaters (excluding first generation Espar heaters), and the only way to increase the altitude tolerance of the heater would be to take it to a mechanic to have the air-fuel mixture manually adjusted. This is not recommended by Webasto and Espar, as this voids the warranty and can lead to unforeseen heater faults.