Truma COMBI 2

[Derek Uzzell]

In Nick Harding’s May 2013 MMM and April 2013 Caravan Club Magazine reports on the latest Autocruise Forte he refers to the vehicle having a Truma Combi 2 heater.

 

I’ve seen occasional mentions of the “Combi 2” before in UK motorhome articles but, as this model doesn’t seem to figure in Truma’s on-line Combi-related information, I thought they were errors. However, having looked at Swift’s owner’s manual, it seems not.

 

Truma’s heater designators have always given some indication of an appliance’s gas-operation output. A Combi 4 has a 4kW output and a Combi 6 has a 6kW output. Logically, then, a Combi 2 should have a 2kW output and this is what Swift’s manual reveals – that the Combi 2 heater fitted to the Forte is a ‘UK Special’ with a maximum heat-output on gas of just 2kW.

 

A Combi 2 can be operated on gas and/or 230V, but if there’s no 230V hook-up available you’ll be stuck with just 2kW. That’s not a lot to raise the living area temperature of a large panel-van conversion like Forte from freezing-cold to comfortable.

 

Although the MMM report addresses the Forte’s heating and says “Truma’s Combi 2 proved up to the job (remember this was January)...”, it would be sensible for potential buyers of UK-made motorhomes fitted with a Combi 2 to be aware of the heater’s less-than-generous output on gas.

 

I assume Truma produced the Combi 2 at the request of UK motorhome manufacturers and that a Combi 2 is less expensive than a Combi 4E. But a Combi 2 should not be significantly cheaper than a 4E and, given the option, an informed buyer would surely never opt for a limited-output Combi 2 rather than the more powerful 4E.

 

Strange...

[Robinhood]

There have been references to the Combi2 for some months, largely in conjunction with PVC ranges as you have found.

 

I also looked for technical references, and couldn't find any.

 

However, the unit isn't simply restricted to the UK, as the only reference I did manage to find was in the Australian distributor's catalogue (Waeco), as follows:

 

[BGD]

I accept that 2kw output isn't a blast furnace, but in a small volume space, relatively well insulated, I'd have thought it would still be perfectly adequate to raise and then maintain a very comfortable air temperature, no?

 

If it's putting out less heat per minute, I assume it's also using less gas per minute too; thus your gas bottle should last proportionally longer.

 

On the very rare occasions when we camp on a site, and thus utilise hook-up, we use a little electric fan-heater. It's 800 watt output is fine for warming/keeping warm our notionally 6 -berth-with-overcab coachbuilt motorhome.

[Derek Uzzell]

The snag with the Combi 2 is not so much its ability to maintain a reasonable air-temperature in a motorhome with relatively small interior dimensions, but its limited capability to raise the motorhome's interior air-temperature rapidly from cold to comfortable.

 

My Hobby has a Truma C-6002EH heater with a maximum 6kW output on gas. My motorhome is undoubtedly better insulated than an Autocruise Forte and the Hobby's interior volume will be not much larger than a Forte's. In cold weather, when I turn on the Hobby's heater, after a short warming-up period it will begin to operate at maximum output. This will rapidly raise the living-area's air temperature and, once a comfortable temperature has been reached, the heater will automatically reduce its ouput from 6kW to 4kW to 2kW and then switch off.

 

A Combi 6 operates similarly, as does a Combi 4 (except the latter's maximum output is 4kW not 6kW). But a Combi 2 has just one output on gas - 2kW. Whereas a Combi 4 or 6 operating on gas will heat a cold motorhome quickly, a Combi 2 will not - it just hasn't got enough oomph.

 

A Combi 4 or 6 will use a lot of gas during the rapid-heating phase, but that phase won't be prolonged. A Combi 2 will use the same amount of gas as a Combi 4 or 6 when all those appliances are ouputting at 2kW, but it will need to run longer to obtain the same 'comfortable' living-area air temperature. When a Combi 4 or 6 has shut down operation (because the required air temperature has been obtained) a Combi 2 will still be running.

 

As a rough analogy think of two cars - Car A with a very powerful motor and Car B with a weedy little engine. Let's say both use the same amount of fuel when cruising at 70mph, but Car A can accelerate rapidly to that speed whereas Car B will appear to take forever. While it may be that Car B proves more economical overall, Car A will be more pleasant to drive and more versatile.

 

Other than a possible reduction in LPG usage (and the Forte is designed to carry an adequate 2 x 6kg gas-bottles) and what must be a small cost-saving to the motorhome manufacturer, there are no technical advantages in choosing a Combi 2 over a Combi 4E. Both are installed in exactly the same manner.

 

I can imagine a Combi 2 making sense in Australia, but I'm not convinced it does in the UK.

[colin]

I would guess a lot would depend on the insulation, this is quoted as 'level 2' whatever that means?

With our van of same size over the last couple of weeks it has only cranked up to 4kw for a few minutes before settling down to 2kw and then shutting down, but after reading Mel's thread where mention is made of draughs around the fridge and ducting running outside I would guess it will struggle. The question is would many people be out in these temps? Last couple of weeks we where often only van on site, wasn't till good friday that we where on a site with a good number of vans.

[Derek Uzzell]

Auto-Trail's website currently refers to their 2013 ranges of motorhome meeting NCC EN1646-1 thermal insulation and heating Grade III classification. This Grade is summarised as "the highest standard for both insulation and heating, such that the interior of the Motorhome can be kept at +20°C when the external temperature is -15°C."

 

Back in 2007, when motothome 'winterisation' was being discussed, Brian Kirby quoted the following extract friom a Caravan Club document:

 

"Caravans built to European Standards (ie models from 1999 onwards) are given one of three grades to indicate the effectiveness of their insulation and their heating systems.

 

• Grade 1 rating specifies a minimum degree of insulation but does not measure the capabilities of the heating system. These caravans should be considered suitable for ‘seasonal’ rather than all year round use.

 

• Grade 2 rating requires the same level of insulation but adds a requirement for a heating system capable of maintaining the interior at 20 °C when it is 0 °C outside. This grade should be suitable for ‘extended seasonal’ usage, or all year round in reasonably favourable climates like the UK.

 

• Grade 3 has a higher standard for both insulation and heating, such that the interior can be kept at 20 °C when it is -15 °C outside. It also requires that all water systems will operate when the outside temperature is -15 °C. These caravans should be habitable all year round in almost any weather conditions.

 

The standard for motorcaravans is somewhat different and has not yet been universally adopted by all manufacturers. There are three grades, but these indicate heating classification, not insulation performance. In fact, there is no specific requirement for motorcaravans to have insulation although clearly most, if not all, will have. Grade 1 means the heating has not been rated. Grade 2 heating will achieve 20 °C inside when it is 0 °C outside. Grade 3 heating will achieve 20 °C inside when it is -5 °C outside and also requires that the fresh (but not waste) water supply must operate when it is -15 °C outside."

 

Without easy access to the relevant standards, I can't say what the present position is. But it should be self-evident that, to obtain/maintain a comfortable interior temperature, a motorhome being operated with the external temperature at -15°C is likely to need a higher output from its heating system than if it's being operated with the external temperature at 0°C.

 

Your Globecar motorhome and the Autocruise Forte are built on a similar base and it would not surprise me if your 'van were better insulated than a Forte. I believe your motorhome has a Combi 4 gas-only heater with 4kW output, whereas the Forte has a Combi 2 with a 2kW output on gas.

 

There's a short report on the Forte here:

 

http://www.outandaboutlive.co.uk/Motorhomes/Reviews/Motorhomes/Autocruise-Forte-Motorhome-Review/_ch1_rw1302_pg1

 

This includes the following reference to the vehicle's heating system:

 

"Despite the fitting of a Truma Combi 2 as opposed to the 4, the Forte does actually retain heat well. The whole vehicle has been tested in Truma’s cold chamber, achieving a Grade Two rating. The only downside here is that the washroom actually gets too hot due to the proximity to the heater."

 

Now, while it might be felt that nobody in their right mind would choose to operate a PVC off-230V-hook-up in sub-zero temperatures, it still has to be wondered why Swift has chosen this low-powered heater for Forte when it's plain common sense that the worse a motorcaravan's insulation the more heater output is likely to be required. Also, why Swift has begun to fit the Combi 2 in PVCs when they used to fit the Combi 4E.