Propane versus Butane for MH heating?

[BGD]

I've been trying to understand some of the differences between propane an butane bottled gas.........../......reason is that at the moment here in Spain in our motorhome we use the "standard" 12.5 kg Repsol butane gas cylinders.

The gas is used by our fridge, hob, oven, and also the Truma Combi water heater/space heater (which was new about 3 years ago).

 

Our bottle-top regulator is the standard 30mbar type, and all the equipment works from it EXCEPT the Truma Combi.

When the butane bottle is full, the Truma works perfectly on both water heating and space heating (or indeed on both functions together).

But once the bottle is down to maybe only one-third full, the Truma Combi "trips out" after a while ( stops working and red light shows on the little panel) - maybe in 2 minutes, up to 5 minutes when set to space heating. It'll still work fine on water heating, it just doesn't like doing space heating when drawing gas for a mostly-used bottle.

 

Any ideas on why?

 

Does it "draw" more gas when burning to supply space heating than when just heating its little container of water?

 

I have heard that these Truma Combis are very sensitive to gas pressure, but I'd have thought that the whole point of a regulator was to regulate the gas supply to the equipment, regardless of the lpg level in the bottle. The regulator is not under suspicion; it's almost new, and this same problem was happening with the previous regulator.

 

 

I can't figure out why this is happening, and the local motorhome workshop are also unsure of why.

 

Now, despite the fact that the Truma seems to be rated to run on butane or propane, each at 30mbar pressure, there is mention in the manual about propane being preferable. It says that one of the reasons why the unit could trip out is if "the level of butane in the gas is too high".

 

So, could it be that somehow the level of butane in the gas being delivered to the unit via the regulator increases as the bottle contents are depleted, the the point where the units safety circuits say it needs to trip out?

 

 

 

 

One other option that I haven't yet tried yet, but am now considering, is to change everything over to propane gas. Propane bottles are available all over Spain in similar sized bottles to the butane ones, so availability is no problem.

So far as I know, all my standard motorhome gas-burning kit (hob, 3-way fridge, oven, and Truma Combi) can all use either type of gas happily, so long as I change the present regulator for a 30mbar propane bottle-fitting regulator.

 

 

 

So, will my Truma Combi prefer propane? Is it more thermally efficient? Anything else I should know about the differences between the two gases in practice?

 

 

 

Any helpful advice gratefully received!

 

 

 

 

 

[Guest Tracker]

Have you tried a different regulator Bruce as they can sometimes deteriorate with age?

That would at least tell you what it isn't if it makes no difference - and a spare is never a bad thing anyway!

 

Does the same burner in the boiler heat the water as well as the space heating or are there two burners?

[Randonneur]

Hi Bruce. We usually use Propane and we are on the Algarve for 3 months and have had to change our Repsol bottle, unfortunately when Martin picked up the new bottle we didn't realise that it was Repsol Butane. The only difference we have noticed is that the hob burns with a more yellow flame. We had a new regulator fitted in September so we know its not that. Previously we had the same problem with the water/heating with the Truma as yourselves and had to have a new Thermocouple fitted. Hope you get sorted soon.

[RogerC]

Beats me...I thought the only difference was that propane remains 'gaseous' in colder climates whereas 'butane' is less so......the following explains this:

 

Butane fuel is commonly blended with propane and/or isobutane.

Both propane and isobutane vaporizes at a lower temperature so they perform better in cold weather.

 

Isobutane vaporizes at 14 degrees Fahrenheit (-10 degrees Celcius) and butane vaporizes at 31 degrees Fahrenheit (-0.5 degrees Celcius). What this means is that at 14 degrees, isobutane is in vapor form and can be burned while butane at the same temperature is in liquid form which makes it useless.

 

I don't suppose with you being in Spain that this applies.

[Keithl]

Hi Bruce,

 

It will be down to the boiling point of Butane, which is only -1ºC. When your cylinder is fairly full there will be sufficient gas boiling off to maintain a healthy pressure and flow but when low this will be insufficient for the demands of your heater.

If you switch to Propane then this boils at -42ºC and so will maintain a good flow right to the end of the cylinder.

 

Have a look at these articles from Wiki...

Butane

Propane.

 

Keith.

[David Turner]

I also have experienced the same problem as BGD - In the UK always use Propane but whilst here in Benidorm we use Butane and have the problems with heating cutting out after a couple of minutes. I made some checks and was informed a lot of the problem is caused by the low evening/morning temperatures.

I have a new regulator.

[Robinhood]

You may have a number of different issues affecting your current gas system, but it is certainly possible that you are challenging the "take-off" capability of your butane supply. I assume you have a combi 4 or 6 unit? (The manuals aren't forthcoming on the consumption for water heating only, but from other reading I believe the gas output is limited to the first "step" in this mode, i.e. 2kW, as opposed to 4kW or 6kW depending on model when the space heating is in use)

 

Propane is stored at a higher pressure than butane, and gasifies (from liquid) at a much lower temperature, hence it is capable of sustaining considerably higher "take-off".

 

If you were in this country with its prevailing temperatures (or if you are considering use in lower temperatures where you are, e.g. mountain use) I would unequivocally recommend a switch to propane, as butane fails to "gas" at about 4 degrees C. Propane will cope with all temperatures you are likely to experience.

 

If you do switch, you will have to replace your regulator, which will eliminate one of the possible causes of your existing butane issues (though, depending on cost, you may just wish to switch your existing regulator and test again).

 

The calorific values for propane and butane are (if you take them by weight - which is what you buy it by) very nearly the same - so the relative costs can be assessed by comparing the cost per kg (the same size cylinders normally contain less propane by weight than butane, and the calorific value by volume - at equal pressures, favours butane).

 

HTH

[tonyishuk]

A passing thought (Whilst passing the local building site where the lower halves of the propane bottles were covered in frost) .

 

Are bottles getting too cold to gas off properly ? If they are mounted in a reasonably insulated location, or the venting holes are not large enough, the surrounding air may stagnate and lower the temprature in the surrounding area thus inhibing the boiling off of the gas.

 

Rgds

 

 

[JamesFrance]

Bruce I am at La Torreta in Benidorm at the moment and have exactly the same as you describe. With a new Cepsa butano the Combi works fine for two weeks, but for another week before the cylinder is empty it is fine in the evening but when it starts up in the morning it runs ok until it turns itself down on the thermostat and then the red light comes on.

 

I am quite sure that using some gas reduces the temperature in the bottle so that the pressure reduces to below what the Combi unit requires. If you can change to propane you would not have a problem unless you have some old gas equipment which needs 37 rather than 30mb to burn properly.

 

We need to keep on the butane as I only have one cylinder and the garage over the road only sells butane, so we cannot wait for the weekly visit by the gas truck. When our Combi goes off we turn on a small fan heater as the van is already warm.

 

This morning was a little warmer than usual and the heating stayed on although our cylinder is low.

[Syd]

 

Wait until I get to Spain if you can Bruce, I may well have all of the propane gear that you will need.

I may not have but I THINK that I have and it is spare capacity.

It was probably there in the caravan when we purchased it so you will be welcome to it.

[BGD]

I've done abit more reading/reserarch, and have also read the other comments here (for which, many thanks guys!)

 

It's a Truma Combi 4 I think (from memory).

The MH is venerable: 1992. The gas bottle cupboard and door is indeed pretty well insulated as it's made of fibreglass all round, and it has two, 12.5 kg gas bottles in it - which leave little space for massive amounts of air to circulate.

The vents in the cupboard door are very small...and there aren't any vents in the floor of the cupboard at all.

I'm starting to think that, as some others have suggested, it might be that the heavy "draw" of the space heating function of the Truma might, when ambient outside temperature is maybe only 8 -10 degrees, and the butane gas bottle is only perhaps one quarter full, and thus gets even chillier as gas is drawn from it, is then just a little too great a required volume for the bottle to deliver - some idiot sensor inside the Truma which is really sensitive to any tiny drop below 30mbar then notices this, thinks there's a gas leak or summat, and shuts the Truma down.

 

This might explain why the "tripping-out" only seems to happen when the Truma Combi is asked to provide space heating and hot water, or even just space heating, but doesn't happen when it's set to just hot water (which I assume "draws", or consumes, a little less gas flow).

 

 

 

 

I'm convinced that it isn't the bottle-tip regulator at fault....as the problem was happening with the previous regulator before I replaced it last year.

 

I don't think that switching to propane is likely to affect any other gas-using things in the MH - hob,oven, fridge - they are all so old that there's no electronics in any of them; I reckon that they are simple: if there's gas of any type, they'll light and thus work.

 

I can't imagine that it might be a thermocouple in the Truma unit that's causing the tripping out - don't they just react to gas flame heat? ie if the boiler flame is burning and thus heating the thermocouple tip, then the thermocouple will just keep the Trumas internal gas supply valve open?

It seems to be something more subtle than that which is just taking some elecktrickery sensor inside the Truma unit just over its tipping point when air temperature is low, butane bottle level is low, and mucho-gas-consuming space heating is what it's then being told to do.

 

 

 

 

I've not bought propane bottles here, (as most people use the 12.5kg bottles of butane as their normal cooking/domestic hot water heating,gas fire heating energy source), but I think that butane is a bit cheaper, and also that it's about 12% more efficient calorifically on a like-for-like volume basis.

But then propane comes higher pressured in the bottle, so I'm thinking that there ain't a lot of difference in overall running costs; especially as both are I understand a lot cheaper than in the UK here in Spain where 12.5 kgs bottles of butane are presently €15.10.

Also, we don't use that much gas anyway - a bottle will always last us for well over a week away in the MH, even when wildcamping all the time so with fridge on gas, cooking on gas, and using the Truma water and space heating a lot.

 

 

 

 

Can someone who uses propane please also advise: Is propane also now used via a standard 30mbar pressure regulator? ( Albeit that I'll need to swop regulators as here in Spain I believe that the design of the bottle top connection to clip-on regulator is slightly different between the two types of gas bottle).

 

[laimeduck]

Many years ago,in the 80's when first caravanning in the Alps for skiing & using camping gas cylinders we could get no gas to the hobs or heater or anything. I realised it was because it was butane, not propane.

 

I got round it by insulating the cylinder in a polystyrene box, then underneath this insulation I made a heat box from an old pipe tobacco tin containing a sidelight bulb. About 30 mins before we wanted gas, I turned the bulb on, this heated the cylinder (safely), the butane produced the gas & we could have a cup of tea & cook a meal.

 

Very Heath Robinson, but effective & worked in temps down to -10 C

I used a wine demijohn band heater (230V) round the cylinder after this & that worked fine.

 

I am now all Propane in "Mabel" our Benima.

[Robinhood]

It all gets a bit complicated from here ;-)

 

The current fixed bulkhead regulator supplied across the EU is a 30mbar unit, and is designed to run on either Propane or Butane. The accompanying installed equipment is rated to run at the 30mbar pressure for both propane and butane.

 

Historically, however, in the UK, propane was delivered at 37mbar, and butane at 28mbar. The accompanying installed equipment was usually rated to run at both the 28mbar pressure or the 37mbar pressure (interchangeably) depending on propane or butane use.

 

German vans (for the home market) were generally regulated at 50mbar, and again the equipment was rated at 50mbar.

 

The difference in equipment (if and where it exists) is generally the gas jet size (being matched to the pressure), and hob, oven, heater, etc should have a plate giving the safe pressure rating(s) and gas type.

 

Depending on your equipment, and the pressure it was first designed for, it may be safest to adjust the equipment if the pressure at which it is fed is changed, particulalrly if it was designed for 50mbar use, unless the rating plate includes the use of propane at 30mbar.

 

Whilst I wouldn't, of course, recommend it to you, for myself, if I were simply switching the gas, but not the pressure, I'd be inclined to give it a try (given current interchangeability at 30mbar without adjustment).

 

It is interesting to note that current Truma equipment instructions indicate an operating pressure of 30mbar (presumably acknowledging the current standardisation), but one of the older ones I've got states "Operating pressure: 30 mbar (or 28 mbar butane/37 mbar propane"

 

 

[Derek Uzzell]

Truma's Operating Instructions for their more powerful combination air/water heaters have always included a caveat about butane usage for air-heating. The vaporisation rate of butane becomes marginal for these high-demand gas appliances, particularly when the weather is cold. Truma mentions a minimum temperature threshold of 10°C but, if you are using 'straight' butane (not a butane/propane autogas mix) the threshold may be significantly higher. Essentially, the heater detects that its gas demands are not being met and it switches to fault mode.

 

Your motorhome's regulator should match its gas appliances. As your Aryal is 1992 vintage, its appliances (other than the retro-fitted Combi heater) will be designed for the 'domestic' standard. So you ought to be using a 28mbar regulator for butane, or a 37mbar regulator for propane. Don't worry about the Combi, as this will cope with either regulated pressure.

[Brian Kirby]

BGD - 2012-01-27 5:57 PM..............................Can someone who uses propane please also advise: Is propane also now used via a standard 30mbar pressure regulator? ( Albeit that I'll need to swop regulators as here in Spain I believe that the design of the bottle top connection to clip-on regulator is slightly different between the two types of gas bottle).

Hi Bruce.

If your regulator is 30mbar and all your appliances work happily on that pressure with butane, AFAIK, they should work equally happily at that pressure on propane. Bulkhead mounted regulators are all now 30mbar, and either gas can be connected at will (subject to having the correct adaptor for the cylinder).

I think it may pay you to try a propane cylinder, and see how the appliances perform. I'd imagine you may have problems with lighting, and even the odd pop while doing so, but can't imagine the consequences being catastrophic.

 

It sounds as though the problem may be temperature related. These is quite a large temperature drop due to the liquid gas reverting to gaseous state, and this may be causing it to fall below the temperature at which it reliably gases. If this is all it is, subject to the appliances accepting the change, propane will fix that.

 

The other possibility that occurs to me is that either the regulator, or the flexible (or even the rigid pipework, or all three! :-)), are of too small capacity to supply the Truma without excessive pressure-drop. The regulators do come in different "sizes" related to the rate of consumption. Not sure about flexible hose diameters, and whether they vary, but it is definitely the case that the fixed pipework must be of a suitable diameter, especially if the run is long, to maintain an adequate gas supply with only 30mbar pressure driving it.

[Guest Tracker]

You could try a hot water bottle in the gas locker when it is playing up and see if that helps the gas to flow better and if it does maybe then try a Propane bottle?

 

[Robinhood]

In reply to Derek - as I'm unsure of the original market for Bruce's 'van, I was wary of assuming what the original design pressures would be (though if the Combi is a relatively new fit, I would be pretty sure that it, at least, would be 30mbar).

 

You are, of course, correct about Truma's recommendation of propane, and the instructions in the Combi4 manual (as below) are clear.

[hallii]

When I used to have the problem of Butane "freezing" I used to put a kettle on first and make a hot water bottle, this was paced under the cylinder and would keep the butane flowing for some hours.

 

H

[Robinhood]

Brian Kirby - 2012-01-27 7:01 PM

 

I think it may pay you to try a propane cylinder, and see how the appliances perform. I'd imagine you may have problems with lighting, ..........

 

I know it's an old 'van Brian, but I don't think it's got gas lighting! ;-) (lol)

 

 

[Keithl]

Bruce,

 

Can you route a hot air feed from the heater into the gas locker? If so this will hopefully keep the bottle temperature above that at which the liquid stops gassing off.

 

I would be very wary about using any electrical device to heat the cylinder, and IIRC, it is actually forbidden to have any electrical devices, eg lights or heating devices, within the gas locker (unless they are specifically designed, eg changeover valves or level sensors).

 

Keith.

[bob the builder]

Always used Propane for all reason stated thus far. However, what is your battery status, if your voltage gets too low, the fail safe cuts in and switches off heating, displaying the red warning light. Poor Venting will also contribute. What's weather like there - Ive just seen three brass monkeys walking down our village high street. Best wishes . Bob

[Syd]

 

The blown air central heating in our caravan has a small pipe offshoot leading into the gas locker to warm the bottles, we use propane so have never had to use it.

 

Think the pipesizes are pretty sure to be allright though because from memory nearly everything I have ever seen has had the same size gas pipes

[Syd]

 

Is this your heater, Combi 4, type plate on side of unit

 

Gas connection

The gas supply’s operating pressure (30 mbar) must be the

same as the unit’s operating pressure (see type plate).

 

The gas supply line (8 mm dia.)

 

Taken from

 

http://www.truma.com/downloadcenter/combi46_installation_de_nl_fr_it_gb_dk_e.pdf

[Brian Kirby]

Robinhood - 2012-01-27 7:31 PM

 

Brian Kirby - 2012-01-27 7:01 PM

 

I think it may pay you to try a propane cylinder, and see how the appliances perform. I'd imagine you may have problems with lighting, ..........

 

I know it's an old 'van Brian, but I don't think it's got gas lighting! ;-) (lol)

Ooh, you are a silly boy..........................................................................but I like you! :-D

[Derek Uzzell]

In his original posting BGD says "Our bottle-top regulator is the standard 30mbar type...", but I'm a mite wary of that statement.

 

My understanding has been that (as a general rule) the current European 30mbar LPG pressure-regulation standard applies only to leisure vehicles, and the 'domestic' standard remains at 28mbar for butane containers or 37mbar for propane.

 

I've done some GOOGLE-searching that suggests that, although the bottle-top connection for Spanish gas canisters may be the same for butane and propane bottles, the bottle-top regulator differs pressure-regulation-wise (ie. as in France). I also found a reference where someone said "Last winter I ran the whole van on a Spanish 28mbar regulator...". Cursory Spanish-language searches also suggest that Spain uses a 28mbar(butane)/37mbar(propane) domestic standard.

 

It is possible to obtain 30mbar on-bottle regulators (I have one that will connect to a Germany-standard bottle), but they aren't that common - that's why I'm uncomfortable with BGD's original statement.

 

If the regulator BGD has been using on a butane bottle is indeed 30mbar and the connection for Spanish butane and propane bottles is the same for both, then he can stay with his present regulator. If it's a 28mbar regulator, then he can swap to a 37mbar regulator when using propane. Whatever the regulated-pressure standard that's appropriate to Spanish on-bottle regulators, that's really what BGD should conform to.

 

UK LPG authorities warn that a leisure-vehicle constructed with a gas system to the 28mbar(butane)/37mbar(propane) standard - which is likely to be the case with BGD's 1992 French Aryal - should not be 'converted' to the 30mbar standard. As far as I can see this is more because doing so would introduce an unknown factor than there being a huge risk. People used to blithely add Truma's Triomatic 30mbar-regulated bottle-changeover system to '28/37' motorhomes (in fact MMM published a DIY article explaining how) and I've never heard of it causing problems. Nevertheless that's what the experts advise.

 

Given the probability that BGD's Aryal's fridge, hob and oven gas appliances are designed to operate using the 28mbar(butane)/37mbar(propane) standard, there's an obvious conflict with his Combi 4 designed to run at a 30mbar 'compromise' pressure. Using propane at 30mbar would be 'right' for the Combi but 'wrong' for the fridge, hob and oven, whereas using propane at 37mbar would be right for the fridge, hob and oven but 'wrong' for the Combi.

 

If my guess is correct that a 28mbar on-bottle regulator is used for Spanish butane bottles and a 37mbar on-bottle regulator for Spanish propane bottles (and it's not possible to obtain a 30mbar on-bottle regulator) then swapping to the 37mbar regulator when swapping to a Spanish propane bottle would best agree with received wisdom. The important thing is to feed the Combi with propane and, if it's not at quite the optimum design pressure, then that will have to be accepted as a inevitable consequence of mixing new gas appliances with old. I don't think it will cause problems though...

 

The solution to this sort of difficulty, of course, is for motorcaravanners to bite the bullet and stick with propane, though lack of gas-flow in cold weather will continue to raise its ugly head when high-butane-content autogas (eg. French GPL) is used with high-demand gas appliances. To counter this, the French gas specialiist Borel now offers heating accessories for refillable bottles/tanks, including a ducted warm air 'slipper' that encloses a bottle's base and an exterior electric 'band' for a tank.