Night temperature maintenance?

I'm planning a grow in a closet (my first ever attempt at growing) and i've come across a problem. I want to do it in a shed that's not regularly heated, and at night can get literally freezing cold. What's the best way of keeping the temperature high enough when the lights are off?

Do a dual flowering room. The heat from one heats the other. Dual ballasts or a flip-flop.

Shed growing is a security issue in general. (but you know your situation better then I)

due to space issues etc. i don't think 2 flowering chambers would be an option (also trying to keep it pretty simple for my first time).

Any idea what a ceramic reptile heater would do to a plant when the lights are off? will it affect it in any negative way? found this in another forum...

"A blacklight produces UVA light. MJ plants require UVB light. Its that simple. You can get a reptile light that produces UVB rays up to about 7%. They sell these cuz lizards also need UVB light for some of their processes. The only thing you gotta watch out for is the heat."

so, it won't have any positive effect during lighting (and i'll keep it off then to prevent overheating)

Watch the heaters. Make sure they don't toss off any light. (and its usually in the red spectrum, can mess with flowering)

UV light for heat? poor choice. You get more heat from the other end of the spectrum (IR)

Maybe one of them oil filled electric radiators?

Ah, didn't occur to me that it might cause problems flowering. I guess just cos i can't see it, doesn't mean it won't fuck up a plant. Would it just tempt the plant to flower too early?
Maybe if it were in an enclosed box so no light can escape?
Thanks for the advice, i'll also look into the oil filled heater option, although space is gonna be VERY tight. Basically planning to build a box inside a fairly small wardrobe.

use a fan heater if space is an issue
like these

http://www.argos.co.uk/static/Browse/ID69/10197898/c_1/1|category_root|Home+and+furniture|10197552/c_2/2|cat_10197552|Heaters+and+coolers|10197884/c_3/3|cat_10197884|Fan+heaters|10197898.htm

did think about a fan heater but noise is also a bit of a problem, it's gotta be super sly! i reckon maybe a bit of playing around with one of those reptile heat lamps and some kind of cover to block out the invisible light might be in order.