I was very satisfied with the Alde system in my Cirrus 820 truck camper.
Alde invented his heating system in 1949.
If you understand convection/radiant hydronic heating (heat moves to cold, heat from the sun gets here without blowing air, the thermostat is not a throttle, the system heats the materials of the interior until everything is at set temperature - floors, table top, toilet seat- , set temp doesn't need to be as high etc etc) you will be happy with it.
It is not capable of supplying endless hot water for steaming 50gallon showers. Normal camping showers are fine.
It will supply heat / hot water on 100% AC shore power electric at 1500 watts, or 750 watt on 15amp AC shore power. If 750 watt is not sufficient, it will supplement with propane so will run on both at the same time. It will run on 100% propane when not on shore power. The combustion and circulator systems are 12v DC from the vehicle.
The circ pump will make a quiet whine when starting, the fluid will gurgle quietly in the resevoir. The gas valve will make a quiet soft thump sound when it closes. To put all this "noise" in perspective when I was camped remote in the quiet desert, the fridge flame drowned out the sound of the heating system.
In -5C early morning hours +15C afternoon cool desert camping with good sunshine, the camper ran on 170watt Zamp solar without operating generator for days in late January - February. Any amount of cloud and a short generator run would be needed daily.
The one advantage a hot air system has (Webastor, Espar, "Chinese diesel heaters", conventional RV screamer furnaces) is knocking down humidity quickly on rainy cool mornings.
Being a hybrid convection/radiant system the Alde does warm the air just not with afterburner speed.
Hope this helps.
