Two questions come up together. Owners of campers with factory heating report the bunk end running far colder than the rest of the trailer, in one case by around 25 degrees Fahrenheit. And owners adding a diesel heater ask where to put it.
The answer to the second question largely solves the first, because where you mount the heater and where you send the air decides whether the cold spot goes away.
Why the bunk end is cold
Factory heating in a camper is usually one outlet, positioned for the living area, with the bunk end at the far end of the trailer behind a partition. Warm air does not go round corners on its own, so the living area reaches temperature, the thermostat is satisfied, and the bunk end never gets there.
It is not a heater capacity problem so much as a distribution problem. Adding a bigger heater in the same place makes the living area hotter and the bunks slightly less cold.
Three things fix it, in order of effectiveness:
- Get warm air to the cold end. A duct run from the heater to an outlet in the bunk area.
- Move the thermostat, or add one that reads where people sleep rather than where the heater is.
- Stop the cold end losing heat, which usually means the skylight and the windows.
If you are adding a diesel heater anyway, you get to do all three at once.
Choosing the heater
A diesel air heater burns diesel from its own small tank or a feed from the vehicle tank, and blows warm air through ducting. It uses very little electricity, which is why it suits off-grid use, and it does not put moisture into the cabin the way an unflued gas heater does.
For a camper, the useful specifications are:
- Output. The 8 kW diesel air heater is rated for spaces up to about 25 square metres, which covers any camper. Oversizing means the unit short-cycles rather than runs, and a diesel heater is happiest running.
- Altitude compensation. A heater without it runs rich at altitude, soots up and eventually refuses to light. If you camp above a couple of thousand metres, this is not optional.
- Control. App or remote control means you can start it from bed. A separate digital thermostat lets you put the temperature sensor where you sleep rather than where the heater lives.
Our comparison of diesel, propane and electric heat covers the choice between them if you have not settled it yet.
Where to mount it
The heater body itself can go almost anywhere with four things nearby: a place for the exhaust to exit, a place for combustion air to enter, a fuel feed, and a path for the ducting to reach where you want the heat.
Under a bench seat or in a low cupboard is the usual choice, because the exhaust and intake can go straight through the floor. Keep it away from bedding and clothing, and make sure the compartment it lives in can breathe.
In an external locker works well if the ducting can be brought inside without a long run. It keeps the noise and any diesel smell outside, and the exhaust routing is simple. The cost is a longer duct run and more heat lost before it reaches the cabin.
Not in the bunk end itself. It is tempting to put the heater where the cold is, but you want the outlet there, not the combustion unit. Noise, and you lose the option of heating the living area properly.
Whatever the location, the unit needs to be mounted rigidly. A heater that can vibrate against a panel on corrugations will announce itself every trip.
The exhaust, which is the part that matters for safety
The exhaust carries combustion gases and it must go outside, sealed, with no possibility of leaking into the cabin.
- Through the floor is best. Short, straight and downhill, with the outlet clear of anything under the trailer.
- Route it away from anything that can melt or burn. The exhaust pipe gets hot. Keep it clear of plastic tanks, wiring looms and the fuel line.
- Away from windows and the entrance door, so fumes are not drawn back inside.
- Sealed where it passes through the floor, with a proper fitting, not a hole and some sealant.
- Angled so water and condensation drain out, not back into the heater.
Fit a carbon monoxide alarm inside. A correctly installed diesel heater is safe. The alarm is there for the day something is not.
Combustion air and fuel
The intake needs to draw clean outside air, clear of the exhaust outlet so it does not breathe its own fumes, and protected from road spray and dust. A short intake with a filter or silencer is standard.
The fuel line from tank to pump to heater should be as short as the layout allows, secured every few hundred millimetres, and routed away from the exhaust and from anything that moves. The pump itself is noisy. Mount it on a rubber isolator, angled the way the manual specifies, and it becomes a faint tick rather than a knock.
Ducting, which is where the cold spot gets fixed
This is the part most installs get wrong, because it is the part that seems least important.
Run a duct to the bunk end. One outlet in the living area and one at the far end, and the heater is doing what the factory heating never did.
Keep the runs short and the bends gentle. Every bend and every metre costs airflow and heat. A duct that goes the long way round arrives lukewarm.
Insulate ducts that pass through cold spaces. A duct running through an unheated underfloor void or an external locker loses heat all the way.
Balance the outlets. If the living area outlet is much closer to the heater than the bunk outlet, most of the air will take the short path. Partially closing the near outlet pushes more to the far one.
Stopping the cold end losing heat
Getting warm air to the bunks is half the fix. The other half is keeping it there.
- Insulate the skylight. A single-glazed roof hatch is the biggest heat loss in most campers, and a skylight insulator pushes into the frame in seconds.
- Cover the windows at night. Thermal window covers or reflective shades cut the loss through glass dramatically.
- Check the seals. A door or window that is letting dust in is letting warm air out. Our guide to dust ingress covers finding the gaps.
If you are on shore power
A small ceramic space heater in the bunk end is the cheap answer when you are plugged in, and it has tip-over and overheat protection for use around bedding. It is not an off-grid solution, because it draws far more than a battery bank can sensibly supply for a night, but on a powered site it fixes the cold bunk for the price of a takeaway.
A sensible order of work
- Insulate the skylight and cover the windows. Cheap, immediate, and it may be enough.
- If not, add a duct from the existing heater to the bunk end.
- If the existing heater cannot do it, or you are off grid, fit a diesel heater with outlets at both ends and a thermostat in the bunk area.
If you send us a rough sketch of the layout and where the cold spot is, we will help you decide where the heater and the outlets should go. Everything ships from Upland, California.