Propane heaters

I am interested in heating my new garden room (see separate thread), but started this thread as I think there may be a more universal application. There are several points.

1) It appears that propane is the preferred gas - does anyone use butane and why one rather than the other?

2) I think I need a 4Kwh heater. But irrespective of the size, there are several different makes - Biogreen Frosty, Lifestyle Eden Professional, GasTec, Regal and Shilton etc. And some are much more expensive than others. Are the expensive ones really any better, and does anyone have experience of any particular make.

3) Reading on another forum, these heaters cut out if the oxygen level gets too low. My garden room, being a conservatory, is essentially air tight and this could happen - though I do have some air vents at the top and bottom. Does anyone have experience of a ventilation problem?

4) And what about the condensation? Are de-humidifiers any good?

5) There are electric and mechanical thermostats. I suspect the electrical ones will have less hysterises (ie difference between on and off temperatures) and hence will save some fuel, but the mechanical ones are independent of the electrical supply and not susceptible to power cuts. Any comments?

6) Do these heaters need to be serviced? And, if you buy one on the internet, and something fails where do you get it repaired. I have never seen a shop that sells them - but perhaps I haven't looked very hard.

7) Do automatic bottle changeovers devices work well?

 

If you have electricity there I would use that. In my experience its cheaper than bottled gas (of course if you can get mains-gas in there than that will be cheapest of all, if not it might be worth considering getting an insulated underground feed from your central heating to a Radiator).

I think electric fan heater, provided you pay £50-ish for a very accurate thermostat, wins for "frost free" because it will rarely come on and the saving from an accurate thermostat will keep it on to a minimum. Fan will shift the heat to all parts of the building (unlike a static heat source).

If you want to heat above 5C then you will need a frequently-on heater, and for that you need the cheapest fuel source. I think you can probably do a straight comparison, based on kW of output - whether burning fuel, or converting Electricity to Heat, you are going to be close to 100% efficient I think?

Bottled Gas heaters have a significant hysteresis, and I think you need a [separate] fan to spread the heat (no bad thing to prevent moulds too). My ideal would be a fan that came on, say, 15 minutes on and 30 minutes off [easy to do with a 15-minute segment timer] but also came on below, say, +5C so that the fan was on when the heater was. I suppose you could wire the segment timer and the thermostat in parallel ...

Bottled Gas heaters generate a fair bit of condensation, Paraffin heaters generate more (and have no thermostat - unless you get a fancy caravan one). I don't think its worth using a de humidifier - a fan will prevent the mould etc. effects of the humidity IME (comparing a dry winter without to a wet winter with - the first had lots of mould, the second none )

If you go all-electric I would also have a bottled gas heater - for power cuts, or hideously cold nights when your electric heater might not cope on its own.

Re: thermostats. I'm not aware that you can get fancy thermostats for Bottled Gas? The £50 ones for electric heating will save you more than the "some fuel" you anticipate. I would expect them to pay for themselves in one season, unless you are buying a posh heater which already has a highly accurate thermostat. No personal experience (I have a fancy heater with a fancy thermostat - I put a logging temperature sensor in the conservatory on a cold night and it maintained temperature within 0.5C ) but people who's opinion I value tell me that their cheap £20 greenhouse fan heaters have a hysteresis of 10C - a 10C overheat is a huge fuel bill, and a 10C underheat is a greenhouse full of dead plants of course ...

We have an automatic gas bottle change-over for the kitchen. It works fine, but there is plenty of useable gas left in the bottle when it changes over, so I now change over manually instead. That's not much good for a greenhouse heater in the middle of a cold night of course!

 

Googled for fuel price comparison.

http://www.nottenergy.com/energy_cost_comparison

Electricity 16.6p per kWH
Propane 73.43p / Litre. Equates to 11.37 kWH / Litre thus 11.54p per kWH (assuming 90% efficient)
LPG 48.0p / Litre. Equates to 6.66 kWH / Litre thus 8.01p per kWH (assuming 90% efficient)

so that looks quite promising (although the thermostat has high hysteresis, so might be same as electricity)

Mains Gas 5.06p / unit. Equates to 1 kWH per unit thus 5.62p per kWH (90% efficient)

 

Kristen - very many thanks for your detailed reply. You have (as always) really given me something to think about.

I found your fuel price comparison link extremely useful. I was aware, of course, of the big difference between mains gas and electricity, but really had no idea of the others costs. Propane is not really that much cheaper than electricity - and I had no idea that butane is even more expensive. Why does anyone use butane rather than propane? It was also interesting to see that smokeless fuel is 50% more expensive to use than ordinary coal. No wonder my neighbour insists on burning ordinary coal in a smokeless zone.

I am almost tempted to just use electricity. Propane is not that much cheaper, especially when you take into account the additional cost of the empty bottles (that you may not get back), and the wasted fuel that the automatic transfer device leaves behind. Not to mention the problem of condensation that means leaving vents open and wasted heat.

But you have a good point about propane as a backup in case of power cuts. The other point is that I am limited to 3 Kwh of electricity as it all comes from one socket in the house, but a gas bottle could provide 4, 6 or more Kwh (at a price).

LPG is cheap, but I am not sure what it is. The name covers both propane and butane or any mixture of the two. I suspect the LPG price quoted is for cars.

I am intrigued and horrified at 10C hysteresis on the bimetallic strips - but not totally surprised. In the past I have used TLC socket thermostats http://www.tlc-direct.co.uk/Products/SMET05.html?source=adwords&kw=&gclid=CPKc-5TR4roCFRSWtAod6RUAoQ at about £17. They worked well, but only last a couple of years or so, which is irritating. Are there better ones? You can pay a bit extra and get an electrical thermostat in a propane heater - which probably has low hysteresis. But its not economical if they fail after a couple of years as that's the whole heater bust, and you are also susceptible to power cuts again.
Again many thanks for a very thought provoking post.

 

Butane stops working at about 1C

 

After warming myself on a LPG heater I'd never use one in a greenhouse.
I can remember feeling wet with condensation from the gas.
It creates water just when you dont need it.

Use electricity, I know power cuts are a possibility, but its clean and convenient, and cheaper than you might think given a good thermostat.

 

Zigs - yes I read that. That propane works at a much lower temperature. If butane freezes more easily and costs more than propane - who uses it?

Pete - Kristen's costs set me thinking and you have confirmed the idea that I might only use electricity. At least for the first year. In the past, plants overwinteed in my house have done much better for me than plants just overwintered frost free. However the frost free ones were in a summerhouse with little light, so they had to be put outside very early in the season into the cold. Now with a proper greenhouse I have got the opportunity to get some early heat into the plants, by keeping them under glass. So maybe I don't need to overwinter plants more than frost free. Really tender ones I will continue to keep in the house.

Electricity helps solve the condensation problem as well. At the last Harrogate Flower Show, I spoke to a consultant to the tomato growers association. I asked about dehumidifiers, and he said don't bother they don't do much - ventilation would be far more effective.

Earlier today I looked at dehumidifiers in a couple of local stores. One model said removes 16 litres per day, which sounded good. But the small print also said that it wouldn't work below 5C and the 16 litres was at 30C and 80% humidity. Logic says that if it removes nothing at 5 C and 16 litres at 30C, ie 25C higher, then at 10C ie only 5C higher it will only remove 20% of the stated 16 litres. The moral is that you have got to read the small print.

 

Peter, butane tends to be used by campers in summer as the containers are lighter than those for propane due to the lower pressure. It is also is used for cookery demos on portable stoves as small cylinders are available. As has already been mentioned butane is pretty well useless in winter as it the liquid doesn't vapourise below freezing point. When I did a lot of camping I took a little butane stove in summer but reverted to an old, heavy (and smelly) primus stove in winter.

 

Dave - brilliant. I knew butane was used by campers, but it never occured to me that its higher boiling point meant that the containers are lighter. Its logical as soon as you think about it.

 

You could do worse that put a greenhouse fan heater in there hooked up to a plug-in energy recorder to see how much you are using. I would recommend a decent thermostat - but the two extra devices push the cost up of course. I think you will find that the cost is modest (well, for frost free, higher temperatures offer greater savings for making the best choice, of course)but at least you would have a baseline to compare against for future years.

Should be easy to do a heat-loss calculation for the building. The materials' U-values should be easy to discover? From that, and the square area of each material, you can calculate heat loss for a given temperature difference across the surface. You might find that you don't need anything like 3kW (I'd be a bit shocked if you do ) - whilst you might need a lot on a -15C night, they don't occur very often of course - and if you had a gas standby then you are sorted for that.

What happens when you are away for the weekend? and what about if that weekend is a -15C one?

We have a dehumidifier (decent sized one). We use it in the Autumn to reduce moisture in the house. The drier atmosphere is much more comfortable, and "feels warmer" thus delaying the need for central heating whilst allowing us to acclimatise to coming colder temperatures

It extracts an amazing amount of water initially - perhaps from all the soft furnishings - but thereafter during the winter it barely collects any at all. I suspect that the colder outside air, entering the house during winter, once heated up has a humidity too low to need any treatment at all. But it might extract a decent amount of water in a conservatory full of plants ... but as I said earlier I don't think its needed (unless you fancy having one for the Autumn, like us, and then also use it now and again in your conservatory). If you find the heater doesn't come on much then I recommend putting it on fan-only to move the air about. Perhaps depends how stuffed your conservatory will be for the winter, you can't move in mine!

 

Had a look at your link. I don't see why its hysteresis shouldn't be good (my experience is that solid state sensors are highly accurate, although they can be a bit slow to respond to temperature change - the time it takes for the component's casing to transmit the heat I guess) - but the temperature has to get to its sensor, which is in the plug unit, and thus by the wall - i.e. cannot be moved.

The sort of thing I was thinking of are the Bio Green ones. They are on an extension cable, and have a remote sensor, so can be positioned e.g. "amongst the plants" where you want to monitor the temperature

http://www.jungleseeds.co.uk/contents/en-uk/d106.html

(Model 2 also has a cooling mode - can't imagine that you would want to pay extra to have that - but maybe I'm missing a golden opportunity?!!)

http://www.greenhousewarehouse.com/pre-wired-electronic-thermostat.html

no idea if that is actually better in practice than the one you linked to ... mine are certainly more expensive !

 

Paying that extra £12 would enable the fan heater & thermostat to be transferred to a greenhouse in summer to use on blow mode for cooling/ventilation.

Those BioGreen thermostats from Jungleseeds are accurate to ± 2°C.

 

I don't think a fan is going to cool a greenhouse - obviously it can, but how? It is going to have to blow air from the inside to the outside, so it needs an extractor fan type fitting, presumably?

It takes energy to run the fan, so IMHO much better to just open a window. If not enough windows then a fan will no doubt help, but IME trying to shift heat from one room to another with a fan is a slow process, so I am doubtful that fan-assisted ventilation has much benefit. But I've never actually tried it ...

... but hence I didn't think that paying extra for a thermostat with a cooling mode was worthwhile. For anyone with an extractor fan fitted it would be mustard of course

 

Again - excellent link thanks Kristen. The difference between my TLC unit and your link is that one is Chinese (I presume) and the other German. Any electronic system should have a fairly low hysteresis compared with a bimetallic strip. But I suspect that a German unit will last a lot longer than a Chinese one. I will certainly get one of those - I'm sorry you can't get any commission. I do applaud Jungle Seeds for stating German or Chinese in their adverts. I think I will stick with their one as it clearly says its German made.

In an ideal world the thermostat with cooling should open electrically operated windows. There are electrically operated roof vents, but not for lean-to roofs. I did inquire about electrically operated ordinary windows but was told that they weren't available. Though they must exist in one form or another.

 

Good point. That thought had not occurred to me, I had ignorantly assumed fan-assisted cooling. Opening vents mechanically does sound like a good idea (although I look at such things as "one more thing to go wrong" rather than as a labour-saving aid. Sure sign that I am getting old!!)