Temperature and air flow

[Stretch1970]

I have a couple of posts on going already but not sure whether to add to those so decided to start a new one. My grow room is 7' H x 8' L x 4' W = 224 Cubic feet
I have two fans moving 134 CFM each so total 268 CFM 6" duct 1 90 degree bend and 8' run on each.
I have one fan reversed pushing 134 CFM cool air in, 6' passive intake and 16" fan to circulate air.

I am growing 12 plants 5 weeks veg and flipped yesterday to 12/12.

I have two 600w hps lights.

My issue is after an hour of lights turning on my temp is up to the mid 90s and stays there. Nights temps are never below 70 the hover between 72 - 74.

My concern is now I have flipped and they start heading upwards heat stress the closer they get to the lights. I have moved them up and only have about another 6 or 9 inches further to move them.

Any ideas or suggestions would be greatly appreciated.

Many thanks

 

[Fuzzy Duck]

Might want to look at getting air cooled hoods to help lower over all temps during lights on as an improvement suggestion.

Sounds like you got plenty of growing height in theory but may suggest you have tall growing strain which might be largely sativa dominate ?


Indica dominate normally double in height once flipped to 12/12 aka if 12 inch tall when flipped it may end up around 24 inch tall their or about etc

Sativa dominate may triple in size once flipped to 12/12 aka if 12 inch tall when flipped it may get up or around 36 inch tall etc

Hybrids well depends on dominate genetics which may influence stuff...


It is just a rule of a thumb guide line at the end of the day




How ever i normally avoid large growing strains as it will test my limited indoor grow area which is only 180cm in height !

Medium strains can be handful at times & pushed me to me limits.


In my last grow i had some well vigorous growth of some 20 inch tall in just under 4 weeks of veg - check old journal in my sig...

I just bent down the main leading stem (apical) with string to control height, i had to do this a few times tho !


By the way most of the pre flower stretch only last 2 to 3 weeks

 

[Stretch1970]

I will have a look at those hoods, my plants are 20 to 22 inches in just under 5 weeks I will have to keep a close eye on them as the stretch.

I thought about swapping the fan on the intake and making it extract like my other two only don't have a filter for it and just having passive air intakes.

Is there any way this could make the temp any worse you think?

Many thanks for you advice and support.

 

[Graytail]

What is your intake temp? Is it the 70 degrees you get as a low? If the intake temp is high, any way of lowering that? Add A/C to the room it's in? That amount of air exchange in a 4x8 should get you lower temps.

And yeah, a couple sealed vented hoods would solve your issue.

Switching the direction on the one blower probably won't make a big difference, and you'd have to deal with the walls getting sucked in. The passive intakes would have to pass a LOT of air.

 

[Stretch1970]

I have noticed the room temp does rise gradually the longer the lights are on, I am venting the exhaust the best I can with out sticking it up in flashing lights that I have any indoor grow. I will have to consider an ac but that will add to the noise, double edged sword. Why is it not good for the walls to suck in?

 

[Graytail]

The sucking walls are no big deal - just have to brace them

But if you're just venting the heat into the room, that's your problem. Your intake temp rises all day.

 

[Stretch1970]

I will have to totally rethink my exhaust venting, do you know or know where I can find the information as to whether there is a limit to what length the exhaust can be before if becomes redundant.

 

[Graytail]

The length of the run isn't that big a problem, especially in a 6 inch - it's the bends that severely reduce airflow. I have a 25 foot run vent, but I have 6 elbows in there. I can't get any more than 50CFM, but my 4x4 vents fine with 1000 watts of lights in there. You're about twice as big, so you could get by with as little as 100CFM if you can get your intake temp down.

 

[Stretch1970]

Graytail, I really appreciate all your help. I have spent an hour or two re routing the pipes so they now vent under my floor boards a good 6 foot in to the space under my living room. After an hour or so my room temp had dropped from the high 80s to mid 70s I am considering a fan just to draw in a bit more cool air from an open window.

Again thank you for your help.

 

[Fuzzy Duck]

Sounds like things are coming along nicely & i do like under the floor boards trick, its been awhile since i've heard of that old one being used !

I myself don't like my night time temps dipping below 70f & most of the time, lights on temps are late 70f apart from in summer months where i may hit low 80f to mid 80's but depends on the day a long with ambient temps from seasonal weather.

But i do like to run my lights on period during r/l night time when temps are much cooler, i use passive vent system so ambient intake of air is a set value most of the time from the spare room i grow in.

Fresh air flow is important also, i just leave window or two open on the security latch & works alright for me.

 

[Stretch1970]

Glad you like my improvisation to venting, things seem to be going OK for my first grow had a few issues along the way and just looking to find a few answers to a couple of leaf issue's I have at the minute.

 

[Stretch1970]

Well I am totally confused, checked my temp 1 hour after lights on in tent 82 room 72 thought looking better checked 3 hours later in tent 101 room 74 pushed windows wide open and open door to room to get some cool air passing through room got room temp down to 63 but still mid 90s in tent. Am I missing something.

 

[Stretch1970]

Thing is it doesn't feel that hot in there, could temp sensor be shafted. Would it break the sensor if I stuck it in the freezer for a minute to see what reading I get.

 

[Graytail]

If the sensor/thermometer is directly in the light, it can read high. I always keep mine in the shade.

If you have another thermometer around the house, try that - a second reading. It shouldn't hurt to test it in the freezer.

100 degrees feels f'n warm! You'd know it - like a blast from a furnace when you open the door. Let's hope it's the sensor.

 

[Stretch1970]

Graytail you are a legend thank you very much for you time and support, moved temp meter out of direct light and temp dropped a good 10 to 12 degrees. I have successfully installed my free standing fan by window to draw in more cool air it took a bit of sorting but managed it in the end

Again your time and support is very much appreciated.

 

[Graytail]

Graytail you are a legend thank you very much for you time and support, moved temp meter out of direct light and temp dropped a good 10 to 12 degrees. I have successfully installed my free standing fan by window to draw in more cool air it took a bit of sorting but managed it in the end

Again your time and support is very much appreciated.

Dynamite! Heat is a good thing - the plants grow faster/better - up to the mid-80s, then they start to suffer unless you add CO2. Mine have been running in the high 80s during a couple heat waves and most of them are doing well in spite of it.