Heating Enhancements

Though the dual LPG and diesel space heating system worked well, a couple of years of use and a good deal of idle thought led to some ideas for improvement. Two areas were identified as candidates for enhancement, these being the locker areas in which the heaters are housed and the truck’s cab.

Cooling The Lockers

Though vented, the under-seat spaces that house the heaters and associated ducting retained an awful lot of heat after prolonged use - and what is more - slowly but constantly built heat the longer the heater(s) were kept running. In short, they could not dissipate heat at the rate they gained it. This was bad for two reasons: 1. the heat trapped in the lockers was effectively wasted; and 2. the heaters themselves were stressed more than strictly necessary by being worked in an ever-increasing ambient temperature.

Some way was required to evacuate the gradual heat built up over the course of a few hours and the answer came in the form of the truly-multi-use Truma Multivent fan. These fans are designed to perform all sorts of duties including cooker area steam / odour extraction, general air circulation, and as an in-line booster to ensure warm ducted air can reach the extremities in very large vehicles.

Fitting was fairly straightforward - once I’d worked out the most space-efficient and unobtrusive mounting option. This task was made somewhat easier as the Multivent will mount in literally any plane and only requires a couple of self-tapping screws to fix. The trickiest part of all was largely aesthetic; involving tapping into the original wiring looms whilst keeping them neat and tidy, and unobtrusively mounting the two-speed fan switch housing.

The Multivent works a treat. After the diesel or Gas heater has been run for a couple of hours or so, switching on the Multivent ensures that the heat that would previously have incessantly built in the lockers is now gently wafted into the living space instead. It means that the interior is heated more efficiently and the heaters themselves are allowed to run in a much cooler environment. As an added bonus, the fan is quiet in operation and only draws about a quarter of an amp (@12V) on its lower setting.

The passenger seat in the cab is a great place to sit and come down after a day on the road. The suspension seats recline and tilt very accommodatingly and the good all round visibility means that the cab space doubles as a comfortable and handy wildlife hide, or just somewhere to lazily watch the world go by. Being isolated from the rear, it’s also a very good spot to reflect on the most recent argument… That said, in colder weather, as soon as the engine was turned off there was no way to heat the space and - being relatively poorly insulated - it quickly cooled down. In reality, this was never a problem most of the time but on winter trips, and when visiting colder climates, the issue was very real.

I considered various ways to combat this including fitting a separate diesel powered water heater. These water heating ‘furnaces’ utilise the vehicle’s coolant and pump it around the engine block and heater matrix, thereby allowing the vehicle's heater fan to circulate warm air just as if the engine was running. An added bonus with this kind of heater is that in very cold conditions they can be used to pre-heat the engine coolant and sidestep any potential cold-start issue. For various reasons, including cost, complexity, potential unreliability, having to run the truck’s heater fan whilst the alternator wasn’t providing charge, and the fact that the truck has reliably started well into the minus Celsius range so far, I decided to abandon this option and stick to the underpinning design philosophy of simplicity and reliability.

And so, following a bit of head scratching, sorting through piles of old heater duct fittings, and having made sure I could source one or two ‘awkward’ bits and bobs, I concluded that extending our current space heater ducting would be the way to go. In choosing this route, the central component that everything else had to be built around was a pre-formed Truma insulated flexible duct that would provide the link from the existing habitation box ducting to the cab. This is sold in 2m lengths and comprises an inner duct of 65mm outer diameter, a glass-mat-like insulating sleeve, and then an outer waterproof duct of 75mm O/D.

I had to shorten the standard 2m length which gave a good opportunity to optimise the lengths of the three constituent components and so maximise the insulative properties. Making the whole ensemble robust and waterproof was a little tricky and required a mishmash of standard Truma parts, some old Propex parts, plus a couple of one-off oddities. The main complications revolved around accommodating the two different sizes of Truma duct and ensuring at least one part of the finished connection was quick-release to enable the cab to be tipped when required.

The final result works well. There is enough power in the habitation box heaters to feed the extra ducting run and this can be further boosted if required by temporarily closing the ducting that feeds the washroom area courtesy of a Bowden cable operated Truma fitting specifically designed for this purpose.

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