Greenhouse heaters .

I have always heated my greenhouses with electic but have been thinking if bottled gas would be a cheaper option .
Looking for any thought's on the type of heater (12x8ft greenhouse) and how for's and against's using bottled gas ..

Dave

 

The fumes from bottled gas can affect some plants, I remember using gas some years back in a public show house when the boilers failed and most of the Coleus and Tradescantias dropped their leaves overnight. I'm not sure if you can control the temperature and you will have to go out and get the bottles too.
I'm sure lots of advice will appear here soon.

 

Dave - I think the choice depends on the temperature that you want.

If its just frost free - I suspect that electricity will be the cheapest. The reason being that you have good control with a thermostat and the electricity only comes on for a short period of time at the peak cold time. The electric heater may not come on for many nights in a row. I use electricity with an energy consumption meter so that I know exactly how much it is costing me - and I have records that show that amount for each night. When I installed the system about three years ago it only cost £3 to keep a 10' x 8' summerhouse frostfree. The last couple of winters have been so much colder that the costs will have been 10 times as much. I have the figures but not to hand.

If you are heating it to a higher temperature an electric heater will be on for much longer. Think of a temperature graph of the winter and then turn it upside down so that the coldest periods appear like the peaks in a mountain range. To just keep it frost free you have to remove the very tips of the peaks - which will be small. But the hotter you keep it the more of the peaks you will have to remove by having the heater on. It is quite possible that for every extra 1C warmer that you keep the greenhouse the heating cost will double (I am not sure of the exact figure).

As the set temperature rises (or the winter gets colder),there will come a crossover point when the convenience of electricity is outweighted by the cheaper cost of gas as a fuel, even if its on when its not really needed.

 

PeterS
Are you saying it cost £3 per night for frost free 10x8 ? or over the whole cold period ?

I was looking at freecycle for an old mini caravan gas heater, and to set it on minimum
Obviously the easiest way is electric, with thermostat control, but at what cost
approximately and average for
A. Frost free
B. Min temp for nurturing seeds/lings

Jack McHammocklashing

 

Jack - I have found my diaries and just updated my spreadsheet.

I have a wooden summerhouse of 10' x 8', which I insulate with bubblewrap over the winter. I use a 1 kilowatt heater and have measured the Kwh used. I have converted that into a cost using my recent rate of 12.5p/Kwh (but it has since increased this month by about 15%). The consumption and costs are for the complete winter.

2006/07 11 Kwh £1.37
2007/08 14 Kwh £1.75
2008/09 27 Kwh £3.38
2009/10 113 Kwh £14.12
2010/11 339 Kwh £42.37

The last year was much more expensive. Mostly it was caused by the cold weather, but was partly caused by the fact that my external thermostat gave up and I used the internal frost free setting in the heater which was set at 4C rather than the 1C that I had been previously been using.

I was using a frost free setting to overwinter a number of tender plants, such as Brugmansias and Fuchsias etc. The object was just to keep them alive but in a dormant state. As the light level was so low in a shed crammed with plants, there was no question of them being in active growth.

Anything I wanted to actively grow over the winter, I took into the house. But then you will still have a problem with the low light level.

The economy of the first few years was because the winters were mild, which meant that, for instance, In January 2007, the heater only came on for 35 minutes during the whole month. This why, to my mind, electricity is so much more convenient than a paraffin heater which has to be left on overnight. However I don't know anything about gas heating - but the January 2007 experience tells me that you must have a thermostat.

It has to be added that there are significant other costs in buying the heater, energy consumption meter and external thermostat.

 

there are systems about where you could have a thermostat on a gas heater and it would only come on as needed but you would need power to the stat and ignition system,might be worth doing more research.
How about having mains gas installed by a pro might work out cheaper long term
something like this perhaps
Bio Green 1.9kw Natural Gas Greenhouse Heater- £119.95 Free Delivery Available