Autogas (LPG) and Motorhomes

[Derek Uzzell]

Graham:

 

Thanks for that information. It's odd that the Dometic manual for Bob's RM7655L fridge and the manual for your RMT7855L oven/fridge combo are in conflict regarding the autogas warning.

 

It would be nice to get a definitive statement from Dometic GmbH itself about this. I've never had much luck getting anything useful out of Dometic in recent years, so, if anyone has a reliable contact in Dometic (or is feeling optimistic!), perhaps they could explore this by contacting the company, please?

 

What needs to be established is whether Dometic is actually OFFICIALLY forbidding use of autogas in all of their 3-way refrigerator appliances (old and new) or, if not, what their advice about autogas really is. It does need emphasising that, as far as I'm aware, Dometic has never issued a statement via the leisure-vehicle press that autogas should not be used to fuel their absorption fridges.

 

 

basil:

 

You don't say what make of fridge is fitted to your neighbour's SEA, but I'm reasonably sure it will be a Dometic product.

 

Dometic's instruction manuals have, for some time, recommended (for large capacity refrigerators) the installation method you describe, where the gas-flue just exhausts into the void behind the rear of the fridge rather than though a chimney-extension leading flue gasses directly to the outside air.

 

Based on the photos in magazine test reports, smaller Dometic fridges (sub 103 litres capacity) are usually fitted with a shallow-height L100 upper ventilation grille that is designed to accept a connection to a flue-pipe extension. Larger Dometic fridges normally have either the double-size L500 upper grille or the middle-size L300 version and neither of these grilles has an in-built connection for a chimney-extension. In the latter cases, if an extension were to be fitted, then it would (presumably) need to be routed to a separate dedicated outlet that was the caravan/motorhome norm at one stage but is only rarely encountered nowadays (see the Swift Mondial photo on page 146 of MMM July 2008 for an example). The necessary bits to do this would be available from Dometic.

 

If one presumes that, when a L100 grille is fitted it is actually connected to a chimney-extension (!!), then the rule of thumb seems to be that, for Dometic 2-door fridge/freezer appliances, no chimney-extension will be used, but, for Dometic single-door fridges, a traditional chimney-extension will still be employed.

 

Our Hobby has a Dometic 150 litres fridge/freezer and the accompanying manual emphasises the importance of hermetically sealing the appliance from a leisure-vehicle's interior. The manual says "If the cavity between the vehicle's wall and the refrigerator is sealed so that fumes cannot penetrate the living area it is possible to vent the flue gas directly through the upper grille. Do not use any kind of aluminium flue pipe (eg. T-piece) to lead the flue gas out. Deviations shall require the consent of the manufacturer"

 

Early experience with our Hobby was that, in windy weather, if the vehicle were parked so that its L500 fridge ventilation grilles faced towards the prevailing wind, then the smell of flue gasses was very noticeable within the motorhome. Refrigerator design makes it very difficult to completely seal the appliance from the leisure-vehicle's interior and still allow the fridge to be removed at a later date for repair/maintenance. Hobby had made a reasonable fist at sealing, but I still had to resort to the time-honoured ploy of shoving foam into the space above the fridge's upper surface to close up that gap. The Hobby's fridge is now pretty well sealed from the vehicle's living area, but I still try to park with the ventilation grilles facing downwind if I know the weather will be blowy.

 

Logically, it must make better sense to take the fridge's gas-exhaust directly to a dedicated outlet - either in the upper grille or separate - rather than let it spew out into the void behind the fridge, but it's often going to be impracticable to retro-fit such an outlet without making major modifications. Certainly I wouldn't consider attempting it with our Hobby. Exhausting the fridge's spent gasses above the roof is probably the best plan (and means that, combined with a below-floor air-inlet, body-side grilles can be dispensed with) but arranging this is likely to prove challenging.

 

(I'm unaware what happens with Thetford fridges, but photos of motorhomes fitted with them suggest that the ventilation grilles don't have integrated connections for chimney extensions. Perhaps someone with such a fridge could comment on how its exhaust gasses reach the outside?)

[JohnP]

I have model RMT7655L fitted in my 2007 Knaus Van. The manual states on page 25, paragraph 6.8 that Town Gas or Natural Gas should not be used. There is NO mention of Autogas.

The manual is edition: T.B. MB 09/2006

 

The manual is the same edition as Happy Chappies but the information is on different pages and paragraphs. Strange!!

 

The flue is vented through the top vent which is behind a cupboard over the fridge/freezer. This is well sealed and to date I have had no problems with fumes entering the van regardless of the wind direction and strength.

 

Quote from manual. If the cavity between the vehicle's wall and the refridgerator is sealed so that fumes cannot penetrate the living area it is possible to vent the flue gas directly through the upper grill. Do not use any kind of aluminium flue pipr to lead the flue gas out.

A lipped seal kit is available to seal the back of the fridge to its housing. How many of these are fitted by manufacturers?

 

 

[Dave Newell]

As far as I'm aware Thetford fridges have the flue terminating inside the void behind the fridge. As Derek has said, assuming this void is sealed from the interior of the 'van then there is no problem but frequently fridges are nto very well sealed/installed. In my opinion (and it is purely that, my opinion) the more traditional exhaust to outside is little better as it terminates so close to the upper vent and therefore if the prevailing wind is blowing against that vent it could well bring combustion products inside via the upper vent.

 

D.

[hapi_chappie]

Due to the discrepancy mentioned by John, I've now delved deeper into my manual, which reportedly covers model numbers: RMT7650,7651 & 7655 and also RMT7850,7851 & 7855.

Page 25 in my manual deals with the Ventilation of the fridge. Page 29 being the Gas Installation as mentioned earlier, which contains no reference to Autogas.

However, on Page 9, paragraph 5.2.2 (entitled Gas operation) it does state that one should not use Autogas, town gas or natural gas!!

So Dometic's own manual suggests that it's OK to install an Autogas supply, but not OK to operate the FF using the Autogas!

Derek, I have no contact directly with Dometic, so cannot comment on their position, although Dethleffs are currently considering whether the "problem" is covered under warranty and are quoting Dometic.

[Derek Uzzell]

These are links to other motorhome forum threads that have some bearing on this subject. Page 2 of the second MHF thread contains feedback from Dometic that may be of interest.

 

http://www.motorhomefacts.com/ftopic-46755.html

 

http://www.motorhomefacts.com/ftopic-40853-days0-orderasc-0.html

 

http://www.motorcaravannersreunited.co.uk/viewtopic.php?t=322&sid=2139f20590b4441e0c2b91068aa23d4b

[Basil]

Hi Derek and Dave,

 

Thanks Derek for your information. Derek, yes it is a Dometic 'double height' fridge but I don't know the model number off the top of my head but it sounds like the one you have described.

The cavity above the installation is well sealed near the top but as you have indicated I still believe there is the potential for flue products to enter the living area as the sealing on the lower part of the housing where the fridge is inserted is less than perfect.

We will pursue the idea of venting the flue externally as the current installation is less than desirable and would certainly be something that would prevent me from purchasing a motorhome with this type of installation. As you have indicated a change of wind direction could allow CO (Carbon Monoxide) to enter the living area if the appliance was burning incorrectly, that to my mind is not a desirable situation.

Venting to outside air will improve the situation and although Dave is suggesting and I do accept his point, that it would be possible to have the products return through the upper vent the likelyhood of entry into the habitation area (IMO) is nowhere near as big a problem as it is currently with the flue terminating near to the top of the fridge unit and the poor sealing around the fridge. The upper vent being approximately one foot higher than the current flue termination would mean that any returning products would be extremely diluted with air, unlike the full undiluted amount that would be issueing from the enclosed flue.

I consider this to be a seriously flawed installation and I am surprised that it has been allowed. I would also advise anyone who has not had this type of installation regularly serviced to do so immediately, to me it is potentially unsafe.

As always just my opinion so it is your choice.

 

Bas

[Derek Uzzell]

Bas:

 

There can be no doubt that the fridge installation on your neighbour's SEA motorcaravan is potentially unsafe as (irrespective of where the flue-gasses emerge), the back of the refrigerator has not been properly isolated from the vehicle's interior.

 

Unfortunately, as I'm sure you are well aware, few fridges are satisfactorily sealed from the motorhome's living area. The reasons for this are manifold - fridge-design makes sealing difficult, motorhome converters ignore the fridge manufacturer's installation instructions, poor workmanship at the motorhome build-stage, etc.

 

The ideal installation would be where, as the fridge is slid home into its surrounding enclosure, the necessary airtight seal is automatically and reliably produced. In practice, what you normally get is air-gaps all round the back of the fridge. If you're lucky these gaps will be narrow and some attempt will have been made to seal them. If you aren't lucky, then the gaps will be open Wooky Hole caverns. Even if the motorhome converter uses a 'sealing kit' from the fridge manufacturer, there will still be a need to do some supplementary sealing. And the more sealing that is done, the harder it will be to extract the fridge from its enclosure should this be required.

 

The Electrolux/Dometic fridge on my previous motorhome (a 1996 Compass-built Herald) had a big gap beneath it and a yawning gap above it: no attempt had been made to seal either gap and no 'heat deflector' was fitted beneath the work-top over the fridge. The outer lower ventilation grille was way too high (Compass's fault), preventing access to the gas-burner assembly and meaning that any leaking gas would have had no choice but to enter the motorhome's interior. I fitted a 2nd lower grille, a sub-worktop deflector and sealed the top-and-bottom gaps. But it still remained impossible to service the fridge properly without withdrawing it from its enclosure as (due to Dometic's cock-eyed design) the gas-flue extensions couldn't be removed with the fridge in place. And, of course, withdrawing the fridge from its enclosure would necessitate unsealing the appliance and then re-sealing it afterward. The Herald's fridge's gas-burner needed occasional attention and I used to resort to the 'dealership' ploy of rapping the gas-flue smartly with a little hammer to dislodge any build-up of muck inside it. I've not seen this technique recommended in John Wickersham's articles in MMM, but it seemed to work for me and, during my 6-year ownership of the Herald, it's fridge never needed to be moved.

 

On my present Hobby it's similarly impossible to service the Dometic fridge/freezer in situ. I did manage to remove the gas-flue extension and I've modified it so removal will be easier in future. But, despite there being a whopping great ventilation grille at the fridge base, I can't get at the gas-burner assembly because it's partially masked by the motorhome's bodywork and (although I've got 6-jointed fingers and a neuro-surgeon's dexterity) I can't reach a screw Dometic uses to retain the burner's protective metal cover. So, if the flue needs to be 'swept' effectively and the burner components cleaned, the fridge will need to be displaced from its enclosure to gain the necessary access. And this displacement will, of course, mean unsealing and re-sealing the back of the fridge. (This is why, if a motorhome habitation service includes a 'full' fridge service, the overall cost of the exercise can sky-rocket.)

 

It will be interesting to learn how you get on with your neighbour's motorhome. In principle, I wouldn't envisage extending the existing gas-flue so that it vents to the outside air being very hard to achieve, though I suppose there's a possibility that doing so might affect gas-burner performance (and it seems to be contrary to Dometic's advice for their 2-door appliances). However, unless you can arrange for the repositioned gas-exhaust outlet to be well away from the fridge's ventilation grilles, I'm doubtful that it would be worth the effort unless the fridge is to be left in it's present poorly sealed state.

 

Me, I'm not concerned that the gas-flue exhausts into the void behind my fridge now that I've improved the sealing arrangements, but I certainly wouldn't have tolerated the original set-up as it was very obvious that fumes were entering the Hobby's interior.

 

It's perhaps worth adding that, although the sealing of the upper part of my fridge appeared pretty good when viewed through the top ventilation grille, when I removed the fridge's control panel and looked from the inside, I could see small gaps through which wind pressure had been forcing the gas fumes. These gaps were very difficult to reach and hard to seal on a non-permanent basis. That's why I chose to insert a plastic foam barrier behind the fridge's control panel to fill up the large gap between the fridge's upper surface and the lower surface of the furniture panel above.

[Basil]

Thanks Derek, all duly noted and a complete reseal of the fridge will be carried out in addition to resiting the flue exit.

Thanks for your information.

 

Bas

[hapi_chappie]

Derek. Thank you for these other references.  it's particularly interesting to see the comments about Dometic offering a modified burner as a solution.  Has anyone else been offered this solution.

I also had comments passed to me today from Dethleffs that are apparently from Dometic:  To the effect that the reason Truma products don't suffer the same issues is that their products burn at a higher temperature and therefore burn more gas. Dometic prioritise on fuel efficiency!!!  Make of that as you will!

I'm still interested in any resolutions people have discovered other than sticking with Calor bottles!!

[Basil]

Hi hapi Chappie,

 

Just a thought, perhaps not much feedback regarding a solution to the problem is because not many people have had a problem, there are lots of satisfied people who have posted above for instance, and perhaps Dometic are as I suggested earlier on an 'a##se covering exercise'.

 

Bas

[hapi_chappie]

My instinct is that you're right Bas. Part of my motivation for pursuing this issue is to ensure that they are not succesful if it is their strategy, although of course I also want my FF working properly :-)

It's been a useful exchange of views and experiences though - so thanks to everyone, including Derek and yourself in particular.

Graham