MMM Interchange "Heating" Letter?

[Derek Uzzell]

On page 220 of MMM July 2008, in the Interchange section, there is a letter from Mr Colin Leake headed "Heating". This letter reads as follows:

 

"If you have blown-air heating it becomes very ineffective in the winter. The reason is quite simply that you are taking the very low temperature air in from the outside and it requires a great deal of energy to heat it. To make matters worse, even when you have managed to heat it you are then blowing the hot air out again. The result is that even if you are on an electric hook-up you may well still have to use gas as well as electricity.

 

The solution is simply to take a small 2kw thermostatic fan heater with you such as the ones used in greenhouses. The 2kw setting will heat the living space up from cold, and normally if the 'van is well insulated and it is not too windy outside, 1kw will maintain the temperature.

 

It makes one wonder when some enterprising manufacturer will wake up to the problem and offer a recirculation setting similar to the one offered on even the cheapest of cars. If you have a convector or wet system then no such problem exists."

 

George Collings's reply is lengthy and I won't quote it in full, but two of his comments include "not all systems draw air from outdoors" and "Gas safety regulations demand motorcaravans have a relatively high rate of permanent ventilation via the floor and roof, entailing significant heat losses even if air is recirculated".

 

I'm perplexed by Mr Leake's letter, as I'm not aware of any motorcaravan blown-air heating appliance that is intended to operate in the manner he seems to be describing. Without exception all such appliances are designed to take in air from within the motorhome, heat it and recirculate it back into the living area. (In fact, it would be a very strange system that didn't work thus, so, if anyone knows of a non-recirculatory motorhome blown-air arrangement, I'd be interested to hear of it.) The technical performance of motorcaravan heating systems is essentially unaffected by outside temperature: it's simply that motorhomes retain warmth about as well as Lady Godiva riding a polar bear in Antarctica and, in cold weather, a motorhome's heating system needs to be run at a higher setting to keep up with that heat loss. But surely this is a basic and self-evident physical principle that everyone recognises?

 

I'm sure it's also well recognised that adequate ventilation of a leisure vehicle's living space is essential for comfort. That's why motorhomes will always have permanent ventilation at roof height and I vaguely recall seeing a table advising how much ventilation should be provided relative to the size of the vehicle. But I don't remember anything about floor-level ventilation being a mandatory safety requirement.

 

Now, I have seen motorhome blown-air heaters installed so that they would undoubtedly have difficulty operating properly in recirculatory mode. These have usually involved Truma combination air/water heaters buried under beds, in corners of kitchen units, wardrobe-bases or 'garages', with minimal (sometimes no) dedicated access provided to the habitation area. Perhaps the worst example was a new Swift Group motorhome where the Truma heater was tightly imprisoned in a below-wardrobe enclosure with no means to obtain air except via a yawning gas drop-vent (with a large "Do not cover" label) in the floor nearby. The reason I happened to notice this was that I had gently touched the wardrobe floor that promptly fell on to the heater beneath!

 

Are inside-the-vehicle gas drop-vents legally necessary in motorhomes and, if so, how are they supposed to function? UK motorhome manufacturers seem to love 'em but my German-built Hobby hasn't got any. The Hobby's gas-locker and fridge are both well ventilated to the outside air, but there are no ventilation holes deliberately cut into the internal floor. As far as I can make out, motorhome drop-vents appear to assume LPG has the density and slipperiness of mercury and that leaking gas will actively cooperate by escaping through mousehole-size floor openings. I reckon this is another UK motorhome 'tradition' (like switching off habitation 12V electrics while the motorhome's engine is running) and that tests of the genuine effectiveness of drop-vents would be very revealing. If they aren't mandatory (and their absence on my Hobby suggests this is the case), are unlikely to work (unless they are unacceptably large) and will certainly contribute to draughtiness and heat loss, what's the point in having them?

 

Regarding Mr Leake's fan-heater advice, Truma offered 230V blown-air heating on the C-6002EH model and (optionally) on the latest Combis. Eberspacher and Webasto also market blown-air appliances with a 230V heating capability. All of these heating equipments recirculate warmed air. I've always carried a cheap mains-powered fan-heater in the motorhome and, although the Hobby has a C-6002EH, I prefer to use the fan-heater if we are on a campsite hook-up in cold weather as it operates more quietly than the below-bed Truma unit. I would guess that a high percentage of motorcaravanners will carry a fan-heater, as emergency back-up if nothing else, and, because this type of heater is so cheap, that's why motorhome manufacturers have tended not to bother to standard-specify blown-air appliances with an expensive 230V option.

[BrianR]

Don't you think that Mr Leake is confusing air used for combustion with the recirculated air for heating? The former is sometimes/always? drawn from the outside and expelled again.

 

I agree that a small ceramic fan heater is more efficient and can be used even when the amperage available is only 3amps.

[Hopesy]

We picked our 'van last november and used it through the winter on hook up with the blown air heating which we found ok. What ceramic fan heater do you use if you find this better and what about infra-red space heaters which are designed to heat you and not the air around you. Any comments? (?)

[trooper]

As a retired heating engineer, I agree with everything derek said.

My bessacarr had a return pipe in the lounge, looked like an outlet, plus there was a hole from outside for combustion air, this has to be the norm.

cheers

[fred grant]

who needs a fan heater when u as alice my biddies???

 

fireyfred

[BrianR]

Hopesy - 2008-07-01 12:37 PM

 

What ceramic fan heater do you use if you find this better and what about infra-red space heaters which are designed to heat you and not the air around you. Any comments? (?)

 

My ceramic fan heater was bought in France, was made in China and has no maker's name. It is thermostatically controlled, has two output levels (max 6.8amps). On the lower setting it seems to heat the 'van as well as the Carver blown air unit does on its full (8.4 amps) setting - leaving aside that the Carver is also heating the shower cubicle (and the clothes in the wardrobe!).

 

I've never had experience of an infra-red space heater in the van, but it would have to be positioned to "shine" on all the people to be heated, which would be a problem in my 'van.

[colin]

Re Derek's initial question, doesn't one of the esbacher? or similier diesel systems have an option of heating the engine water and then using cab heater, I know I've seen this somewhere, seems very ineficienct to me.

Re electric heaters, I prefer a oil filled rad, only noise is click of thermostat, and a bit safer if acidently covered.

Re Infra-Red, would need carefull positioning in a van to avoid hot spots

 

p.s. after a quick look found this.

Webasto water heater systems use either the vehicle’s own heat exchangers and ducts around the instrument panel and fascia or, if available, uses additional heat exchangers built into the vehicle.

 

I wonder if some of the vans I've seen that offer deisel heating are doing this?

[Derek Uzzell]

Colin:

 

Diesel-fuelled heaters for motorhomes essentially fall into two categories.

 

One type is similar to a straightforward gas-fuelled blown-air appliance (eg. Truma's E-Series products) where a flame warms up a metal heat-exchanger that in turn passes its heat directly to air that is then blown round the interior of the vehicle.

 

The other sort of motorhome-suitable diesel-fuelled heating appliance uses fluid as the heat-exchange medium. This is closer in principle to a household central heating system (or Alde's LPG-fuelled 'wet' heaters for leisure vehicles). A flame warms a heat-exchanger that heats fluid that, in turn, transfers that heat to air that is blown around the vehicle's interior. This type of appliance can also provide 'domestic' water heating and may offer the capability of being integrated into the motorhome's original base-vehicle heating/cooling system. In the latter case this means that, while the motorhome is being driven in cold weather, free domestic hot water can be obtained. Vice versa, when the vehicle has been stationary with its motor inactive, the motorhome's heating unit can transfer heat to the vehicle's original heating/cooling system, warming up the motor for easier cold-starting and allowing immediate hot air to emerge from the cab heater.

 

This is necessarily just a shorthand overview and you really need to get hold of Eberspacher/Webasto documentation for a more complete picture. To identify the heater types, the brand-names currently used are:

 

Eberspacher:

"Airtronic" - pure blown-air heaters

"Combitronic" - air + water heating systems that are either modular or 'one box'

 

Webasto:

"Air Top" - pure blown-air heaters

"Thermo..." - modular air + water heating systems

"DualTop" - 'One box' air/water heater specifically designed for below-floor mounting

 

All sorts of dinky add-ons can be specified for certain of these appliances, including programmable controls/timers and activation by phone/text message.

 

It may also be worth mentioning that an increasing number of light commercial vehicles are being fitted with diesel-fuelled cab-heaters as original equipment and that it's sometimes possible to obtain kits for these that allow the heating capability to be extended beyond the cab area.

[dshague]

IT WOULD BE NICE TO READ THIS MONTHS MMM

BUT NOT RECIVED MINE YET .

ALSO SUBSCRIPTION DPT NOT REPLYING TO MY EMAILS

CUSTOMER  SERVICE PASS ON THAT

[Derek Uzzell]

dshague:

 

Aren't you being more than a mite optimistic expecting MMM's magazine subscription/distribution people to recognise and react positively to an off-topic complaint hung on the bottom of a technical-subject thread in one of several Out&AboutLive forums?

 

Personally, as there's never any certainty that an e-mail will reach its intended recipient (never mind the recipient losing or ignoring it!), I never use e-mail as a communication medium for anything I rate as important to me.

 

Don't know if it's of any relevance, but, when I renewed (by phone) a subscription to MMM not too long after the expiry date of the previous subscription period, I was told that the next issue of MMM could not be sent to me as the distribution deadline had been passed. My own fault for being tardy.

[dshague]

would like to say i got a response to my posting on here last night .you will surprised who reads postings on here. my mmm is now in the post .thank you mmm.

sorry i used a off post subject to make my point.

 

[Mel B]

Hopesy - 2008-07-01 12:37 PM

 

... what about infra-red space heaters which are designed to heat you and not the air around you. Any comments? (?)

 

Do you mean the tall things that glow and some swivel? If so, don't bother with them in my view. I've currently got one burning my left leg/side whilst my right side/leg is cold. They are nice and bright (if you need a light as well!) but I don't rate them for heating up anywhere. Much better with a good fan heater especially if it also has a cool air function for the summer. I only use my 'glow' heater as it's quiet, otherwise I'd have fan heater on. If noise is a problem, then a good old fashioned convection heater is the best option. They warm up quickly, you can leave them on a low setting all night as they don't keep you awake, and you can 'hover' over them to get a burst of heat up your PJ top in a morning ( :D)

[Guest peter]

fred grant - 2008-07-01 7:45 PM

 

who needs a fanny heater when u as alice my biddies???

 

fireyfred

:D

[Derek Uzzell]

peter:

 

Don't understand why you've quoted Fred Grant's earlier comment and just added a green grinny.

 

Oh yes, I see now - it's a clever play on words based on modifying Fred G's previous posting so it reads "fanny heater" rather than the original "fan heater".