It would seem to me, that controlling a heater with a thermostat makes more sense than trying to second guess the weather. As for a household timer: few of them are rated to handle the wattage an electric heater uses, so be careful on that route regardless of your decision.

While it's true that load ratings on any electrical appliance, from heaters to cords, plugs and timers are rated with caution in mind and can likely handle more than their labels would indicate- why risk at best, blowing out the timer or circuit, or worst- a fire?

BAD IDEA for all of the reasons above and more.
Buy a thermostat

I have two common inexpensive timers on my fans so that they shut off and come on at intervals to give the plants a break. I'm just careful not to get them wet and both are at least 4' above the floor.

I don't have timers on my heaters. Two are plugged into therm's from Kkontrols.com and the third I only turn on if it's going to be in the teens at night. If you do put your heaters on a timer (bad idea I think) make sure they're the heavy duty type and keep them away from water.

They do make Industrial timers that can handle that load but they will cost you MORE than a thermostat so it would make no sense to use one because you still have no control over the temp.
Just saw the forecast for today high of 20F with periods of sun.
This is why you MUST use a thermostat when the sun comes out the temps will soar and if the heater was on a timer not only would it cook your plants but it would be a waste of electricity.

Most of the electric heaters come with their own thermostat.

dcarch

Posted by dcarch (My Page) on Wed, Feb 20, 08 at 7:40

Most of the electric heaters come with their own thermostat.
dcarch
Yea and all of them that I have had SUCK

Farmtek has some reasonable priced ones that are ready to go. you just plug the heater into it and set the temp. Pretty cool!

Here is a link that might be useful: farmtek thermostat

Just try and get one set to keep the temp at a certain point. I gave up after numerous trips to the GHs to fiddle with the temp knob. They don't seem to go by the temp in the room but buy TIME per setting.

thanks for all the input...I guess the idea was not a well received one...I think that a small oil filled radiator heater or even a little forced fan electric one if turned on and left on, will NEVER get the GH as hot as it is during the days..so even if it runs all night, I dont see how it can hurt anything (except my electric bill).

So for the few hours we are talking about, maybe the best timer I already have (MY ALARM CLOCK), set for whatever time frame the temps are supposed to drop...I can always double check the thermometers before turning it on...(I'm currently using a long extension cord running from the house...so all I have to do is open the back door and plug it in.

Again thanks all...I'll figure out what works best from some trial and error I suppose :) Rome was not built in a day...so they say

rjinga: greenhouser is right about extension cords. A firefighter friend once told me that the majority of house fires in winter were found to be the result of extension cords for electric space heaters.

If you have an outdoor recepticle, running an insulated, grounded outdoor electrical line underground from it to your GH would be a fairly simple project. You don't have to trench very deep; just enough to make sure you don't drive a shovel into it when you garden. Then you could lay down an 8 gauge line and with a 30 amp breaker, run your heater with no worries about fires or shorts and have juice inside your GH. Use ONLY- GFIC recepticles.

The worst mistake people make in installing electrical wiring in DIY projects isn't that they can't figure out how to make simple connections, but in chintzing on the materials. Meaning: the cost difference between lighter and heavier guage for outdoor extension wiring is too small not to use the heavier. It's always better to have extra capacity in any line, than to overload it.

Since homes use 12 gauge wire some only use 14 gauge putting a 8 gauge wire and a 30 amp load on the outdoor weatherproof box will result in tripping the 20 amp breaker or in worst case start a fire.

Their is nothing wrong with using an extension cord if you use one heavy enough for the job.
Most people use those cheap lamp cords they are 16 gauge wire.
If you use a 10 gauge extension cord then the lightest part of that circuit is the house wiring since it is
12 gauge
People caution against using extension cords but they should warn against using small wire nothing wrong with extension cord when it is sized correctly.
If you need to bury the wire you want to be sure that you buy underground cable DO NOT bury Romex house wiring.

You commenters need to be careful on your suggestions, poeple take this comment section as the gospel. Please find a qualified electrician to do any household wiring, I would hate to see your house burn down because of a comment from a DIY expert.