A question of heat

Howdy folks,

I have two questions:

How much will one 600 hid raise the ambient temperature in a 12’×14’×9’ closed room?

How much will a 600 hid and a 250 hid (850 total) raise the ambient temperature in that same size room?


Well there are several factors to consider what is the ambient is it insollated? what’s your air exchange rate like humidity how many hours do you plan on running the light. Mainly are you concerned it will raise your temps too much or are you looking to gain a few degrees? I run a 1000w hps in a 11x8x8 but do need to vent during lights on since my indoor ambient is 68f gets up to 83 by lights off during lights off I run extraction fan but it pulls heat from my veg room running a 600w mh

I plan on keeping the room sealed, I’m not planning on ventilating the room, just the 600 hid into the room, away from the immediate plant tops.

The room is going to be both heated and air-conditioned depending on the season, so I guess what I’m asking is about how much heat will each respective unit generate?

I’m going to put the 600 in a 4 X 4 X 7 grow tent and use the 250 for veg in the closet


Am I’m wrong? I was assuming that a specific wattage light would produce a set amount of measurable heat?

for this you are certainly right but since I have always used ventilation to bring in fresh air and extract warm oxygen rich air so have had little need to do the research I do know a 600w bulb in a 7 foot tent with no venting will kill your plants

That’s exactly what I’m trying to figure out!

I’m trying to figure out what temp I have to heat the room up to and then how much the grow lights will add.

I’m thinking if I bring it to 60, and venting it into the same room hopefully I’ll get around 70 which should be fine, I also have some heat mats for my reservoirs if needed.

I haven’t grown in 21 years and have things changed! I’m using my old 250 and picking up a 600. I’m hoping to buy and set up everything right the first time.

… I certainly appreciate any and all help so thanks in advance, and thank you again Donald

I live in Northern Canada so I use my lights to heat my grow space and yes a dry run is the best way to know for sure

I’m sitting here going on 9 a.m. and it’s still 10 below zero where I live (it’s cold) it made me think of this post because I’m still kind of not knowing the answer…

what I’m really trying to ask is if I use one of my unheated rooms, or even heat it to (eg.) 50 degrees, add a 4 X 4 x7 grow tent, a 600 watt unit in the tent, a ballast outside in the 50 degree room, what temperature should I expect inside the grow tent in that 50 degree room?


my cellar stays at 59-60ish at nite…
3 1/2’ x 3 1/2’ x 6’ tent
when my 600 watt mh @ 400 watts is on…house heat is on (70F) heat bounces around 75F-81F near the plants in my cellar …on the higher end with low humidity, adding a cool mist humidifier dropped the temps to 75F (and better heat management)…at night, heat off, temp went down to 60F in 6 hours of darkness. Light schedule is off 7PM to 1AM…18/6
1 exhaust fan, lotsa passive air leaks…I leave the door ajar on the tent, a few 6" vents

btw, our area broke a record last night -18

Thanks for that 411! I’m pretty sure it’s going to be manageable and I don’t mind heating it to 50 (ambient) for a few months… I have a small wally world heater (1500 watts) with a little fan I could add for nights like last night…

Congratulations on your new record! We set one last night too … what happened to global warming?

It’s warming this is the first year I can remember where I didn’t get atleast 2 weeks colder than -30

Oh… You’re having a heat wave up there! :slight_smile:

been above zero for almost 2 weeks now will be back to work soon at this rate if not for the rain

If your grow space is completely sealed you are going to run out of CO2. You need some type of incomiong fresh air to replenish the CO2 that the plants will use up very quickly unless you plan on supplying CO2 artificially. I use a carbon filter to get rid of smell and the fan that powers that is exhausted out of my ceiling into the loft of the building. Over my plants I cut a hole in the ceiling and installed a 4" axial fan so I have access to fresh air. During the first few weeks of veg I don’t need the filter so I shut it off its fan and turn on the 4" axial fan. When I turn on the blower for the filter I turn off the axial fan because with the filter being exhausted to the loft I have a low pressure area in the room which is good for the plants and incoming air through the ceiling turns the fan on its own, not that that is necessary. Of course, I could be all wrong. Good luck. Keep it green.