Calor/butane heater duration calculation and maintenance

[dave]

I have a "Valor Robocab" butane heater for the garage and would like to know how long (in theory) a should last on a new 7kg refill. (data below) The one I have here doesn't seem to last as long as it did - but maybe that's just imagination.

Do these heaters need cleaning somehow?

When it finally fails to light at all, there is still liquid sloshing about in the tank. It is very cold in the garage so the gas pressure is lower - but still seems a lot of liquid there.

It is difficult to start when cold (the ignition spark is strong), but have to keep it clicking away for a minute or so before the thing "latches" on. (Thermocouple?)

For the duration calcs:- The data plate says

2.84 kW/hr 9690 btu/h

(And 204G/hr - don't know what the heck that is)

[Roger Chapman]

No idea.

If you have liquid you still have some vapour pressure but butane is poor at low temperatures at the best of times and the less there is left in the tank the more heat evaporation sucks out of what's left.

I don't know for sure but it could be 204 grams per hour which would suggest approaching 35 hours duration for 7 kg of gas.

[Huge]

There's your issue. Butane boils at -0.5 deg C, so doesn't work that well in very cold weather.

Change to propane.

[Tim Downie]

As any caravaner will tell you, butane is rubbish at low temperatures. Even if you've got a lot of liquid gas in the tank, evapouration levels drop off sharply as the ambient temperature drops and declines even further as the latent heat of evapouration chills the butane even further. That's why they switch to propane if the weather's cold.

Sorry, not a lot of help to you I know. ;-)

Tim

[Ronald Raygun]

Perhaps the regulator is on its last legs. I don't know if they can be adjusted.

You could test whether it's temperature-related by taking the heater into the house overnight and seeing how well it lights in the morning, then taking it back into the garage.

It shouldn't say "kW/hr", that would be kilowatts per hour, which is a unit which is not particularly meaningful. It should say just "kW".

The amount of energy the heater converts into heat each hour is 9690 BTU or 2.84 kWh.

Note that BTU and kWh are units of energy, while BTU/h and kW are units of power. But I digress.

It's undoubtedly the fuel consumption rate in g/h.

Given that the heat of combustion of butane is about 50 MJ/kg (or about

14 kWh/kg), a consumption rate of 0.2 kg/h is entirely consistent with a power rating of 2.8 kW.

So there's your answer: 7 kg of fuel should last about 35 hours.

[dave]

Thanks all anyway - at least I know the reason now.

[Steve Firth]

That's 204 grammes per hour so 7Kg should last about 28 hours, give or take. A 7Kg bottle is extremely small and as others have advised butane is a rubbish fuel for winter use. That's why those of us who have to use bottled gas (a) use propane and (b) buy in large quantities. Even a 13kg propane bottle will save money over the price of a 7Kg butane bottle.

If you want to retain the current heater, don't mind spending some upfront cost and have a friendly local LPG garage then you can get refillable lpg bottles. These are legal to refill but the cheating, robbing LPG suppliers try to instill doubt about these safety. This is bollocks but it may stop some retailers from allowing you to fill the bottle at their pump. If you have a look around you will find the bottles but most suppliers scared of the LPGA will only supply them for fixed fitment in a caravan or motohome with a fillpoint attached to the vehicle.

I use a propane catalytic heater in the garage, cost £60, uses 13Kg cylinders, does a damn good job for the money. Cylinders last me about a week in use.

[Huge]

I turn the radiator up.

[Chris J Dixon]

I did hear of a Swedish caravanner who, when it got too cold for propane, was in the habit of lighting a candle to keep the chill off his gas cylinders. I guess Darwin could well come in to play here.

Chris

[Harry Bloomfield]

Butane will not evaporate to gas at winter outdoor temperatures - it is only really useful for summer or indoor temperatures, in which is why in winter they all switch over to red bottle propane. To be sure that is the problem, you might try pouring a kettle of boiling water over the butane bottle.

[Huge]

[Tim Downie]

Not used a candle but have had to use a hair dryer & fan heater to boost gas output when we got caught out in a cold snap one year in our caravan. ;-)

Tim

[Roger Chapman]

I have a twin burner and Calor (butane) bottle I use when camping. In winter I have been known to park the bottle on one burner while cooking on the other. ;-)

[Dave Liquorice]

Now that's interesting but surely LPG(*) from a garage has road transport duty on it (about 30p/kg?) pushing up it's price or is the markup so much on ordinary bottled LPG such that road LPG is still cheaper?

[dave]

Thanks again all. This ng really is a gem. I now know why this heater was only 15 brand new at the car boot :-) Still, I have used it quite a bit for the 'ol hobby stuff in the garage in winter. I am sure (from what you have all said) that it is purely the low temp that is the problem. Take pity men - I'm in the garage wearing a balaclava trying to repair the 'scope which blew up a few days ago - just when I needed it to check stuff on a homebrew tacho circuit for ancient car (diy best traditions) - then onto fixing exhaust clamps to some old conduit for framing at the allotment (we have some excellent strawberries this past summer - and now trying raspberries on said frames. Steel tools can get amazingly cold to handle... It seems I must look for a Propane heat rsn.

ps "It shouldn't say "kW/hr", that would be kilowatts per hour, which is a unit which is not particularly meaningful. It should say just "kW"." Indeed so - I wrote some extra characters in the hope the friction would warm things up a little :-) (Best excuse I can come up with)

tvm

[Dave Liquorice]

Just keep the cylinder in the house. Take out to garage when you want the heater, 'tis only a piddly 7kg one after all.