1st grow - minimum temps?

Thanks for running a great community site. I have been reading all I can and am dying to get started. I haven't tried growing in about 18 years! But then it was a footlocker in my bedroom....

Planning a grow in a shed in the Northwest. I can keep temps down when the lights are on, but how cold can I let things get at night? Will the glow from a space heater upset the plants?

The space will be 4.5' wide by 3' deep by about 5' tall. I am planning 2-400 watt HPS, with floros to begin with. Should I keep the floros running on the sides when I switch to the HPS?

Has anyone figured out a way to 'harvest' the heat generated by the lights so you can use it to keep things warm at night? I have been thinking about a water loop from the lamp into the ground below the room, but I also think of stupid ideas like feeding tuna fish mayonaise.......

Peace,
Banzai

Sounds like a fun setup to work with!

Advanced Nutrients "scientists", claim the ideal tempurature fluctuation is - 15° F during the lights-off cycle (both during veg @18/4, 16/8 or during Flowering @ 12/12).

Green light will not affect the plants during the dark cycle so maybe a filter of some sort can help, maybe - double check that.

I would definately put the floros on the sides, there are no reasons not to!

Harvesting the heat... ... ... Solar water heaters? Your grow room would look like something out of a Bond film.

How cold will it get during your flowering cycle and how well is the shed insulated?

Thanks for the feedaback. Nighttime temps run about 50degrees F, so I will need something if a 15 deg drop is recommended.
Green lights can work, I just need a way to see when the HPS is off.
I am just trying to avoid wasting all that heat, doesn't seem natural to vent everything during the day and then run a resistance heater at night. I suppose what I really need is some thermal mass. I can put in a layer of insulation, then some bricks.

I'll be back with more questions.

Just thought of one-Good source for HPS lights? I can buy bulbs at Lowes/Home Depot for $22/each, but need a fixture (ballast?)

You can buy complete setups online, fixture, ballast and bulbs in one discreet shipment.