Greenhouse heater

I have one of 200 watts and would like to know if this can be run safely from a 10 amp cable. Thanks for any advice.

Reply to
Ariadne
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Yes.

Whether 200W is enough, is another matter though. Is this a soil heater or propagator? 200W isn't going to do very much for space heating.

Reply to
Andy Hall

On 17 Dec 2006 09:06:52 -0800 someone who may be "Ariadne" wrote this:-

Possibly.

How long is the cable? What protective devices are fitted to it? How is it installed?

Reply to
David Hansen

Thank you. It is really just an anti-frost device.

Reply to
Ariadne

The 10 amp is a 10 metre cable and I would rather use this than a 40 metre 13 amp one. I'd plug it into a circuit breaker.

Reply to
Ariadne

On 17 Dec 2006 09:35:15 -0800 someone who may be "Ariadne" wrote this:-

Using the shortest possible is a good start.

One in the house presumably. That's also good.

You didn't say how it was to be installed, so I imagine that it is to be laid over bare ground and/or paths. It is not possible to make such an installation safe. As well as people tripping over the cable there is the possibility of frost damaging the insulation, which will then break off when handled/troden on, the cable being crushed in a door or window and a host of other things.

For short term use Arctic cable would avoid the insulation problem though not the other problems

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the real solution is a proper supply to the greenhouse. That will make it as safe as possible. The heater would then just be plugged into a socket in the greenhouse. However, if you live in England or Wales the Labour Party have added pointless bureaucracy to such work, as a result of which people appear to be running cables on the ground to avoid the nonsense.

Reply to
David Hansen

Even as just that, I would be surprised if it's enough.

Are you putting some insulation inside the glass? Bubble wrap is generally used and helps save some heatloss while still allowing light.

Either way, I'd suggest a test. Use two thermometers - one inside and one outside.

For half of the day, have the heater turned off and note both readings once an hour. I would expect them to be close and for the inside to be a little warmer possibly.

Then turn on the heater and continue the measurements for the rest of the day. What you are looking for is how many degrees above outside temperature that the heater maintains the inside temperature. You should reach a point where the inside temperature tracks the outside even if the outside is changing.

Since the outside is only a few degrees above zero at the moment, you can reasonably assume that the inside, with heater on will track the outside fairly well.

Now let's say that the difference ends up being 2 degrees. If there is then a drop in outside temperature to -3 degrees, the inside would probably end up at -1 degree and you would have a problem.

If this does prove to be the case, you can work out reasonably well how much heat is needed. For example, if the illustration I have given turns out to be the case and you want to have a 4 degree difference inside to out, then you would need a 400W heater and so on.

Strictly speaking, there are a whole load of contributory factors, but doing the sums on a linear basis would put you in the right range.

Reply to
Andy Hall

Thank you for all that. The cable just has to go round a corner and can be kept close to a wall with part of the roof sheltering it and it shouldn't be a trip hazard. I could sheath it in pipe insulation if we

have a freeze. Arctic cable for next year.

I do live in England and appreciate the political comment too!

Reply to
Ariadne

Thank you for all that advice. I'm far from being a great gardener and wouldn't really have thought past the basics so all this is very much appreciated. Method is extemely helpful.

Reply to
Ariadne

On 17 Dec 2006 10:18:28 -0800 someone who may be "Ariadne" wrote this:-

If the wall is a brick one then the cable could be run in a conduit fastened to the wall. When you do the full installation next summer that conduit could be used for the final cable route.

Reply to
David Hansen

Its better plugged into the mains, generally,.

Reply to
The Natural Philosopher

800W heats half our house (Aga) down to pretty low temps.
Reply to
The Natural Philosopher

Why? its only taking an amp, if he runs it from the mains...one assumes that is what he means. 50 meters of 10A cable is safe enough and won;t drop the voltage at that rating..only issues are shock protection if it gets buggered around with..

Reply to
The Natural Philosopher

On Sun, 17 Dec 2006 19:08:23 +0000 someone who may be The Natural Philosopher wrote this:-

You have answered your own question, at least in part.

Other answers are in other parts of the thread.

Reply to
David Hansen

Sexist.

Reply to
Ariadne

Many thanks.

Reply to
Ariadne

the basics have been answered, ie thats its 0.8A so is fine on 10A flex.

200w will cost around 2p an hour to run, so if thats on say 24 hrs a day for 1 month thats 0=2E1kW x 24hrs x 31 days =3D 74kWh at 10p each thats =A37.40.

But with no insulation it wont have much effect on temp, maybe a couple degrees at best.

NT

Reply to
meow2222

Thank you. I once had a shed with thermoplastic roofing and it stayed so warm and dry I kept newspapers in it for years. Accidentally - they were behind shelving.

Reply to
Ariadne

And 200W makes a bulb glow _really_ bright.

A properly insulated house is _quite_ different from a greenhouse.

I'd go so far as to say a 200W heater - unless a soil heater - is actually useless. For a small greenhouse - 20m^2 of glass - 200W will raise the temperature by some 1C or so, neglecting wind losses.

IMO, a 1Kw fan heater, with a frost stat is about the minimum that'll be effective.

Unless it's an insulated greenhouse of course, or with relatively little glass.

Reply to
Ian Stirling

Yes, but your house isn't a small single glazed building... or are you in trouble with SWMBO again? ;-)

Reply to
Andy Hall

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