Hi
First caution! I use electric heaters also. All greenhouses are a natural for moisture so alwys be alert to the danger of electricity and water.

Most electric heater have two control knobs, one is on/off and the other is temp. control. There are no degree markings on the temp control so you must put a regular outdoor thermometer in the greenhouse. turn the heaters on and observe what temp is reading on the thermometer when the heater shuts down. Mark the position of the knob. the knob can be advancer a little afterwards and the real temp noted for the higher setting, mark that position on the knob, and so on.

For soaring daytime heat build up I purchased a regular 12 inch attic vent fan and matching louver. It comes with a thermostat built in. I then cut a hole up high in the end wall of G/H and mounted it as per the instructions came with it. Use the out door thermometer to calibrate the vent setting if necessary also.

Many catcus enjoy lower temp. at nite. Research natural growing conditions the type's of catcus to find the avg nite temp.

There are many other solutions to these problem's, this is my way of dealing with the problem, it worked for years in my old greenhouse and is working fine in the new one..
SO SOME OF YOU OTHER FOLKS GET OFF THE STUMP & JUMP IN HERE AND HELP,

Beescorner, no need to shout :D

I assume you're using a "milkhouse" type heater. I use them as a sort of backup. I set the real GH thermometer for 60, then with the GH at 60, I turn back the so-called thermostat on the electic heater until it goes off. That way if the temp drops under 60F, the heater will kick on.

You could do the same thing. Let's say you want 60F. Let the temps drop to, say 62F at night, then dial down the heater thermostat knob just until the heater turns off. Then when it drops a little more to 60F, it should kick back on. It may take a couple of tries to fine tune it, but then you shouldn't have to be checking the GH more than once or twice a day.

SB

Get a cheap indooor/outdoor thermometer and put it in a shaded/screened spot. (both sensors)

They have a max and min memory.

That way you can be sure that your setup is maintaining the minimum you want.

Also fans are a must with electric heat, you need to move the warm air around, especially at night.

Ditto what Chris said.

It is possible to get a vacation. You'll want someone reliable to keep an eye on the GH, but not to regulate the temps...rather, to keep an eye on the plants!

Ok thank you all so very much.
I do have a min/max thermometer installed in some shade inside. And yes, the heaters are just as discribed, kind of "milkhouse type" with fans. The actual temperature I would like to keep around is 55-60. I am finding it hard to keep it regulated mostly on sunny days,when the temps seem to sore inside. Overcast days seem a lot easier to deal with. Night time seem easier to regulate, it has already gotten down to 28% a couple of nights here and the heaters have kept out the chill.
Should I install a couple of automatic vent openers perhaps, to help with sunny days?

Much appreciated for all the kind help!

Anya

Here is a link that might be useful: Greenhouse

Yes Anya,

You need an exhaust fan (like Beescorner describes) with vents opposite facing them and usually the "intake vents" are on the bottom (Exhaust - top).

On thermostat of course (here's a product that's cheap) and is an inside the greenhouse thermostat that will kick your exhaust fan on and off that I purchased at Menards here in Illinois. "Thermostat Ductstat" - it like your heaters needs to be hand calibrated as to when it will run your fan.

Dax

{{gwi:306817}}

Ok thanks again SO much for everything.
Dax, I will check at the local Menards here and see if they have them. I am thinking now I will be so much better off, with all the understanding I am getting here in this forum.
Thank you all again!
Anya

Dax

Thats a handy way to control the fans. Do those folks have a web site? We use an line voltage thermostat its calibrated but cost $65.00 each I could calibrate it myself if they cost less. We are buying parts, fans ect right now for my mushroom spawn run grow out house.

As for venting, a cheap option is Nikota programmable vents. They're battery powered devices designed to be hooked up to a duct as an indoor room vent. They allow you to customize the temperature inside a given room by opening and closing to the heating/cooling system (there's a winter mode and a summer mode). I got one on ebay for under $25. The batteries reportedly last for years; I haven't had mine long enough to find out. It's a true thermostat, not one of those "adjust up or down until you find the right temperature" things.

Notes:

1) I made the mistake of insulating the vent blades themselves. Bad idea. The motor is very weak (to save power), and can't move much. Insulation should be above and/or below the vent.

2) They're not a perfect seal when closed -- but good enough.

3) They're quite easy to install in a thin film glazed greenhouse, but I imagine it would be tricky if you have polycarbonate panels and don't want to damage them (and near impossible with glass).

So far, I'm pretty happy with my little greenhouse. I've got a 41 cfm DC computer case fan ($5) and four 1W solar panels ($25) to hook up (since a vent on its own isn't enough to do the trick), but I haven't had the time yet, and since it's an unseasonably cold October up zone 5a here (cloudy, daily highs 8-16C; normally are ~18C), it's not a high-priority task. ;)

I'm kind of a "on the cheap gal". Occasionally things come back to bite me, but I'm usually pleasantly surprised.

Karen,

Where did you buy the computer case fan. I'd like to get a couple.

MollyD