Our diesel heater is too big; why, and what can you do about it?

After putting off permanently installing our portable diesel heater for so long, I finally bit the bullet and put it in over a couple of days, and it works brilliantly, as expected. However, there’s a major problem; it’s too big!

What do I mean by this? Even on the lowest setting that we can put it on, the camper trailer gets warmer, and warmer, and warmer, and as it turns out this is a pretty common problem.

Yes, we can get away with it if the temperatures outside are very cold, but when they’re not below about 3 degrees, the heater is too big to run even on its lowest setting.

Diesel heater in place
Our diesel heater is too big when installed permanently

Why is it too big?

When we first purchased the portable diesel heater, I got a 5kW one, knowing it would be outside, sucking cold air in and heating it up via a duct to our camper. As it turns out, this was a good move, as we could leave the heater on the lowest setting and it would keep the camper warm all night, without having to adjust any settings. There were a couple of occasions where we’d have to open a window a bit, but they were few and far between.

If it was really cold, we’d bump it up a few Hertz, from the lowest setting of 1.4 to around the 1.8hz, and it was perfect.

The biggest difference here though, is that it was outside, sucking cold air, and as a result it took more energy to make warm air. Now, we’ve got it installed inside the camper trailer, and its recirculating the air, meaning the longer it runs, the warmer the air going into the heater is, and the warmer it becomes coming out, stuck in this giant loop.

Portable Diesel Heater
As a portable unit it was sucking in cold air externally and having to work harder

We’ve not tried it on any really cold nights (like 3 degrees and below), but even on an 8 degree morning if I turn it on, the camper soon hits 20 degrees, and continues to rise. We’ve not had it get unpleasantly hot, but we haven’t run it for more than a few hours at a time either.

They don’t turn off

Despite what you might think, these heaters are not designed to cycle on and off to maintain temperature. Perhaps this is done to conserve the energy required to run the glow plugs, but they will not turn off when they hit temperature. If they are at the lowest setting already, they’ll just keep ticking along until you manually turn them off.

The only exception to this is if you hack the controller, using one of the advanced controllers that some people are using.

Changing between Hz and Celsius

When we got our heater, I found out you could swap between two methods of control. The first is Hz, and relates to the pump speed. You can adjust it between 1.4 and 5Hz, and the higher you go the faster the pump goes, and the more heat you get.

If you set it to Celsius, it will heat at the required rate to maintain the temperature. For example, if you set it at 15 degrees, it will crank until it hits this, and then back off to maintain temperature. As above though, if the lowest setting makes it over 15 degrees, you’ve got limited options.

The lowest setting on ours is 8 degrees, and I believe this makes the heater run much cooler than the lowest setting on Hz.

Diesel heater display
You can set any temperature you like, but if the lowest setting is still too hot you have a problem

What to do if your heater is too big?

If you fall into the same category as us, and have a heater that is too big, you really have 5 options:

Live with it, and crack a window or two

This is the simplest, and most effective way of managing the temperature. If its getting too hot, just crack a window and let some heat out.

Windows open for air flow
Cracking a window to let some excess heat out is a good intermediate solution

Get an advanced controller

There are a few ways you can run a different controller, which will stop and start as required, using the heater that is too big for your application.

Suck fresh air in

You might find its not too hard to duct air in from external to the unit, like a portable diesel heater does. This means it will need more energy to create the same heat, and you’ll likely be fine for heater size.

Replace the heater with a smaller one

If you have a 5kW heater (which is what a lot of people get), it will be 13.5cm x 13.5 cm x 38.5cm long (check dimensions), and these are realistically too big for many vans and RV’s.

You can remove it and replace it with a 2.2kw unit, which is far more appropriate for these applications.

Tune it to run less warm

It is possible, with the right access code to drop the fuel pump hz below its normal minimum, but this is supposed to be done with a CO monitor and have the fan speed adjusted too. It also means that the combustion chamber runs less hot, which results in soot build up and is generally not recommended. It is an option though.

What are we doing?

I’m going to take the lazy way out again, and see how it goes. We can easily crack windows if needed, but the intention going forward is to turn it on as needed, instead of trying to maintain the camper at 15 – 20 degrees all night.

It seems like when its really cold it doesn’t heat the camper up beyond what we want too quickly anyway, so its not a major issue. So far its working fine, but I just accept that I’ll probably have to manually turn it on and off as needed. It’s so nice having a diesel heater that you can press a button on a remote and have your camper warmed up in minutes that I don’t really care!

We haven’t used it a huge amount since starting our lap of Australia, but it has been turned on when we’ve been drenched with rain outside, or have been chilled by the crazy winds in South Australia, or arrive back into the camper and its freezing. We don’t normally run it for more than an hour or so though, and have never run it over night yet.

Is your diesel heater too big? What are you going to do about it?

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