Why do temps go up at night?

I've searched and didn't find an answer.

I have a Homebox S (31.5" x 31.5" x 63" - 6.89 sq. ft.). We have central A/C set on 76 F 24/7. I'm running 16 26 watt CFL's and 4 14 watters. The ocsillating fan runs in the box 24/7 as do the lights. The exhaust is handled by a 500CFM fan pulling through a DIY carbon filter. Our plants are still vegging so everything is on 24/0.

During the day, the ambient temp inside the box runs from 81 to 84 degrees. At night, the inside temp will get up to 91. I just can't figure out why the temps would go up at night with no changes to the set up.

Any clues?

Lemme guess... the fan runs only during lights on.
At lights off, the fan shuts down. But the lights are still HOT from having been on, and the room will actually spike up to its max temp in the half hour or so after the lights go off...
If your thermometer has a probe that allows you to look at it from outside, take a peek at what the temps do at the end of 'day'. You may be surprised.

To fix, put the exhaust on a different timer that comes on at lights on but shuts off an hour later.

Why not keep the fan on all the time?

does your AC come on @ night ?

Stinkyattic ~ The lights, inside fan and exhaust fan are all on 24/0.

Trancefusion5 ~ The fan is always on.

veggie ~ Yup, the A/C is running at night. Our outdoor lows at night only dip into the 80's.

I kinda figured it's a ventilation issue since at night we aren't peeking in on the babies every so often and no one is moving about the house. Last night I tried leaving the zippers at the bottom front of the box open to let in more intake air. I checked it this morning and the temps during the night ranged from 79 to 84. I get that same range during the day with the zippers closed.

I guess I should get my site nomenclature down pat. When I said "24/7" I meant 24 hours/ 7 days a week. I suppose it should have read "24/0" for 24 hours on/ 0 hours off.

I appologize for the confusion. Please bear with me. I'm new to this and learning something new every day.

The only things on a timer are the lights. But right now, they are on 24/0. The exhaust fan and the ocsillating fan do not run through the timer and are always on. The "cold air" humidifier gets turned on when the humidity drops below 40%. It is outside the tent but aimed at one of the intake panels.

Thanks

Have you tried monitoring what is running for a couple cycles, taking notes hourly on temps, humidity, and what is running at that time, including items on thermostats and your humidifier?

Looks like you will need to improve your passive intake as well. Try moving items that may be blocking air flow.

I'd definitely take a look at your intake. Didn't notice any specs on that, but it sounds like it isn't cutting it. If you are like me... during "daytime" you check on those babies ALL THE FLIPPING TIME. This creates a serious change in airflow which will, most likely, keep your daytime temps controllable. I would guess that if you went without checking on them... you would notice that low 90's temp during the day as well. Even if you open up and look twice a "day"... that is (insert time of visitation) minutes that you have open/free air flowing. When you sleep and the plants are still chillin' in "daytime"... that is (insert time of sleepings :hippy:) hours of ininterrupted airflow... allowing heat to build up. Those precious visits during the day probably remove a great deal of that stored heat.

And 20 CFL's??? Holy shiiiip :stoned:

P.S. Take a picture of your set-up. We like pictures :jointsmile:

I haven't done a hourly monitor. It's been more haphazard, at best. I think both of you, stinkyattic and TheMetal1 have hit the nail on the head.

The intake is passive and limited to the 3 flaps at the bottom of the tent plus a 4 inch duct coming in at the bottom. It did better last night with the bottom zippers open and allowing more air in.

I'm thinking of redoing my exhaust, as well. Right now I have a DIY carbon filter running into 6 inch flex duct and then to an 8 inch 500CFM duct fan. I have the fan mounted outside (on top) of the tent. My thought is to eliminate the flex duct and just connect the filter directly to the fan since each bend in the flex duct cuts down the CFM.

TM1 ~ Here's the pic you requested. The fixture will actually hold up to 22 CFL's. When we go to flower mode, I'll be running all 22 but with 2700k bulbs instead of the 6500k ones in there now.

Damn lookin nice! :thumbsup:

Thanks trance........

Well, I removed the flex duct, getting rid of the bends that were certainly cutting down the CFM of the exhaust fan. The filter is now mounted directly to the exhaust fan. The fan is still on top of the tent, outside of it.

After re-doing the exhaust and filter, I closed up the tent. The temp was at 82.5 F. I have a second digital thermometer outside the tent with a temp probe inside at canopy height so I can check the temp without opening the tent. Each time I've checked it, the temp is a bit lower. Right now it's down to 79.9.

I'll keep checking throughout the rest of the day and check the night time max and min temps tomorrow morning.

I really appreciate everyone's help and input.

Thanks,

McT

Last nights temps ranged from 79.5 to 81.9.

I now feel better about moving on to the flowering phase.

Thanks