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Diesel Interior Heaters

How to heat a motorhome is an ongoing source of enquiry, particularly with a CMCA Rally in Tasmania in many people's plans. Curiously, not a great deal appears to have been written about this subject and, as a result, many turn to Internet forums for advice.

These forums can be wonderful sources of information, but sometimes suggestions are made that are downright dangerous. Caravan and motorhome heating is a sadly common example.

Time after time one encounters potentially lethal advice. Here are a few examples: heat your vehicle by inverting a clay flowerpot or steel saucepan over an open gas ring; turn the gas oven on with the door left open; use a charcoal-burning cooking pot as a space heater. All are extremely dangerous - especially the last.

Heating a small enclosed space by burning something presents two main dangers. The first and most serious is carbon monoxide poisoning. Carbon monoxide is a colourless and odourless gas (slightly lighter than air). It is formed whenever any carbon-based substance (which is most substances) is burned with an inadequate supply of air. Even when there is adequate air, carbon monoxide is produced if the burning reaction is only partly complete.

Carbon Monoxide

Even in small amounts, carbon monoxide is deadly to all warm-blooded animals. A 0.2% concentration can kill within 30 minutes. I can find no local data, but 300 Americans are killed and 10,000 need major medical treatment [because of carbon monoxide poisoning) each year. A high proportion of those are campers, 'travel trailer' and motorhome users.

Carbon monoxide kills like this. Haemoglobin in the blood normally transports all-essential oxygen throughout the body. Unfortunately haemoglobin is massively addicted to picking up carbon monoxide. If there's any around, haemoglobin will grab 250 parts of carbon monoxide for every one part of oxygen. This rapidly deprives the brain and everything else of that vital oxygen.

There are only minor indications: headache, nausea, fatigue - and then unconsciousness. If you were asleep at the time, the odds are against your ever waking up again. Carbon monoxide is rightly called the 'silent killer'.

Direct Oxygen Deprivation

The second hazard is direct oxygen deprivation. Just by breathing we contaminate the air. We take in about a half a cubic metre of air every hour and convert about 4% of that into carbon dioxide. As a result the exhaled carbon dioxide level rises and the available oxygen level falls. The latter can however drop from its normal 21% or so, to as low as 15% before symptoms (such as fatigue) set in. Whilst rarely, if ever, a problem in a home, oxygen deprivation through this cause can be serious in an unventilated space - heated or otherwise. This was tragically demonstrated in England when a number of 'illegal' migrants were asphyxiated inside a sealed truck.

Heating in Confined Spaces

It is essential to keep the potential for danger in mind when planning a heating system for a caravan or motorhome. In Australia at least, our Gas Installation Code legally closes the door against the worst offenders (but not against foolish Internet advice). "Where a [gas] air heating appliance is installed in a confined space the circulating air shall be ducted and be separated from air for combustion and draught diverter dilution'. This effectively rules out mostly anything run from gas - including catalytic heaters.

Yet despite constant mortalities, America seems less concerned. There, it is legal to use catalytic heaters (at least in most States). Historically, the British too had a seemingly cavalier approach to heating. Many British-made caravans were fitted with coal and even charcoal burning stoves (some older readers may remember the coal and charcoal burning Piver stoves that were installed).

Electrical heating is the simplest, safest and cheapest form of heating, but it necessitates a 240-volt mains supply. But for heating away from the 240-volt umbilical cord, there are few heating devices more effective and practical than the diesel powered units that are rapidly gaining favour in caravans and motorhomes worldwide.

The Diesel-Powered Heater

These devices draw air from outside into a tiny sealed furnace that can be housed almost anywhere in the vehicle. Diesel oil is injected and ignited in this furnace. The 'burnt' air is then expelled to atmosphere. Air within the area to be heated is blown across the outer skin of the furnace and ducted to wherever desired. The burning gas is thus totally sealed from the air that is heated within the vehicle.

My first experience with this technology was considerably less than happy! I imported a Finnish diesel-powered unit that worked fine for two or so weeks. But thereafter it would generate no heat - only huge volumes of evil-smelling cold and wet grey/white 'smoke'. For reasons that are still unclear, the thing had a hugely complex computer control system. The whole and quite large unit proved totally unfixable without being returned to its maker on the other side of the world. I fought it over three or so years - and finally gave up. (The unit was briefly described, but fortunately not recommended, in the first edition of 'The Campervan and Motorhome Book'. The mention was deleted in editions thereafter).

I next became aware of the Eberspacher range of diesel heaters. These are highly respected in Europe, the USA and Canada, but do not seem to be widely promoted in our market. Few Australian caravan, campervan and motorhome owners seem aware of them. I was wary of buying a product that lacked widespread distribution and decided to give this one a miss. Then, whilst at the Casino Rally I was intrigued to see Webasto's generally similar unit installed and working in a demonstration motorhome.

The Webasto Heater

The smallest unit in the Webasto range is the size and weight of a large can of soup - and weighs little more. It is far simpler and hugely more rugged than the unfortunate Finnish device, and is very much better made (quite stunning in fact!). This unit produces ample heat, even for big motorhomes.

Learning of my previous experiences, Webasto's Roger Phair kindly offered to make one available to me for long-term evaluation - probably with some trepidation as I describe things as I find them. But he need have no qualms!

The main heater unit is best floor mounted as both the intake and exhaust are on its underside. A separate very small electrically-driven pump, hose and filter may be connected to a separate diesel tank - or can be tapped into the main vehicle tank (as we did with the OKA). A small electric control panel may be mounted wherever convenient within the vehicle.

The hot air vent can be taken wherever desired via approximately 50 mm flexible hose. We made up a small duct from a couple of adjustable vents left over from the OKA's coach beginnings.

Whilst we elected to evaluate the Webasto air heater, the company (as with Eberspacher) also have a water heating version that feeds radiators throughout the vehicle. Via an additional heat exchanger (calorifier) it can also supply hot water on demand.

The Webasto Heater in Action

Where we live on the Indian Ocean north of Broome, winter is not known for being cold. But inland it's a different matter entirely. There, temperatures can drop quickly below freezing after sun-down. But even then, on its lowest heat setting, the Webasto keeps the OKA's interior at a comfortable (for us) 27 degrees whilst using about a fifth of a litre of diesel an hour.

Unsilenced, the exhaust can be a trifle intrusive to those outside the vehicle. It would not be noticed in most situations, but a few users report that neighbouring campers have asked that the unit be turned off at night. A quick check with Webasto however produced (an optional) tiny and very effective silencer (Derringer would be proud of it!).

Speaking of 'comfortable temperature' the US ASHRAE 55:74 standard defines it as 'that condition of mind which expresses satisfaction with the thermal environment'. That self-referencing definition is praised in associated academic comment as being a 'model of clarity'. I'd hate to see their example of an unclear one!

It's too early to advise on longevity, excepting to note that the Webasto unit is very ruggedly made and, as it is designed for much colder and more generally arduous American and European winters, it should have an even longer life in our milder Antipodean climate.

The product is already being offered as an optional extra by at least one leading Australian caravan maker.

For further information see www.webasto.com.au

Further information regarding associated matters can be found in the author's associated books, particularly 'Motorhome Electrics - and Caravans Too!'; and 'The Campervan & Motorhome Book'.

 

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