# How can I maintain the heat in my Grow room tent



## iloveit (Jan 19, 2008)

How do growers maintain the heat in grow tents especially in the smaller grow tents?
Do they keep a small heat fan in their with a thermostat or oil heater,or does the HPS ligths take care of that?

Im really confused on at this point...


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## Al B. Fuct (Jan 20, 2008)

Depends on the ambient air temp around your op. If you live in Alaska, you're going to find it harder to control temps well enough to grow in your garage than most. 

Most grows are harder to keep cool than keep warm. A thermostatically controlled exhaust fan is the starting point. The HPS lighting and ballast will provide plenty of heat for most grows (unless you're in Alaska...  )If you can't keep your temps under 28C, then other measures are required. Move the HPS ballast/s outside the grow room airspace. Use cooltube/s. 

If your grow gets too cool in lights-off hours, add a dehumidifier. They can make enough heat to keep an op above 16C as well as keep humidity from spiking due to your thermostatically operated exhaust fan that won't be triggered during lights-off. Free distilled water, too.


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## VictorVIcious (Jan 20, 2008)

> If your grow gets too cool in lights-off hours, add a dehumidifier. They can make enough heat to keep an op above 16C as well as keep humidity from spiking due to your thermostatically operated exhaust fan that won't be triggered during lights-off. Free distilled water, too.


I don't think I had ever read this before. Is there a setting for the rh that you use? VV


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## iloveit (Jan 20, 2008)

Good starting point for me, thanks!


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## psyclone (Jan 20, 2008)

I had a huge winter condensation problem with my hydro system in a grow tent, in a garage, also low temps during lights out. A cheap thermostatic fan heater sorted it right out-temps between 70/75 now and ends humidity by drying the air out (takes a day or two of fiddling with the thermostat).
Al B. has it right about the cooling I think, I usually grow outdoors when temps rise. This year, fully formed and flowering girls are going out for the Spring 12/12 photoperiod. Two outdoor crops a year I hope


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## Al B. Fuct (Jan 20, 2008)

VictorVIcious said:


> I don't think I had ever read this before. Is there a setting for the rh that you use? VV


yeah... always on, 24/7.  If I had a more powerful dehumidifier, it would not run all the time, but the little one I have runs constantly when set for 40%RH.


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## Al B. Fuct (Jan 20, 2008)

psyclone said:


> I had a huge winter condensation problem with my hydro system in a grow tent, in a garage, also low temps during lights out. A cheap thermostatic fan heater sorted it right out-temps between 70/75 now and ends humidity by drying the air out (takes a day or two of fiddling with the thermostat).


The only problem with heaters is that they are expensive to run. Most draw about 1000-1200W even on "low." 

A dehumidifier draws about 300W, making a little bit of heat while dehumidifiying.


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## psyclone (Jan 21, 2008)

I count not the cost, compared to the agg of going out, paying too much to fill my stash, and then doing it all again next week, but for the Summer months, dehumidifier could be crucial. Again with the good advice Al B. I won't rep you again or people will talk.


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## Al B. Fuct (Jan 21, 2008)

Dehumidifiers are most useful in winter. If the ambient air around the grow is very cool, thermostatically controlled exhaust fans may not run often enough. No grow should be allowed to go under 16C; a dehumidifier may put out just enough heat to keep the kids happy. 

In summer, ambient air temps will often be high enough to trigger thermostatically controlled exhaust fans all by itself. A humidistatic switch can replace a dehumidifier for summer grow room operation. Your local building trade supply house will have thermo and humidistats.


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## psyclone (Jan 21, 2008)

I shall check it out.


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## natmoon (Jan 21, 2008)

Al B. Fuct said:


> Dehumidifiers are most useful in winter. If the ambient air around the grow is very cool, thermostatically controlled exhaust fans may not run often enough. No grow should be allowed to go under 16C; a dehumidifier may put out just enough heat to keep the kids happy.
> 
> In summer, ambient air temps will often be high enough to trigger thermostatically controlled exhaust fans all by itself. A humidistatic switch can replace a dehumidifier for summer grow room operation. Your local building trade supply house will have thermo and humidistats.


Yeah man this is a good idea.
I have a mini oil radiator in mine it only uses 700watts on max setting but the idea of the dehumidifier providing the heat and removing excess moisture whilst budding is a great idea combating mould and only using 300 watts.

I will save up for this idea +rep to albfuct


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## psyclone (Jan 21, 2008)

..So little heat. 300 watts go in, maybe 100 watts of heat come out. If it's real cold, you need more, I can see me getting a dehumidifier for summer though.


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## Al B. Fuct (Jan 23, 2008)

Every grow is different. 

Most grows are located in utility spaces; garages, attics, basements, etc. Rarely can one spare a climate controlled bedroom- _and_ cope with sharing stinky grow room air with the rest of the house. Some folks DO have the luxury of full aircon and heating to keep temps bang on 24-26C @ 30-50%RH, 24/7/365. The rest of us have to cope the best we can. 

My coolest winter ambient temps rarely fall below 12C. The dehumidifier is enough to keep the grow room at 16C or above with lights off. If your ambient temps get to 0, you're likely going to need more than the waste heat from a dehumidifier to get the room to 16C or more.

However, in summer, with my ambient temps ranging from ~22-28C, the dehumidifier is useless. The exhaust fan is often triggered in lights-off by ambient air temp, moving air through the op faster than the dehumidifier could ever possibly treat it. Regardless, in summer, the dehumidifier is on a timer so that it runs only during lights-off, for those cool lights-off times when the exhaust thermostat isn't being triggered. When the 1000HPS lights are on, they're making more than enough heat to keep the exhaust blower running pretty much all the time (winter or summer).


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## psyclone (Jan 23, 2008)

So move a lot of air in summer. More catalogue browsing then... Who makes a good, quiet powerful fan? I guess it's better to get something reasonably profesional, it will be working pretty hard. Any thoughts?


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## FilthyFletch (Jan 23, 2008)

Just take your intake fan and flip it so its outside the growtent hook your long silver duct hose to it and run it to a heat vent from the closest point you can now draw warm air in from your homes heater.


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## Al B. Fuct (Jan 23, 2008)

psyclone said:


> So move a lot of air in summer. More catalogue browsing then... Who makes a good, quiet powerful fan? I guess it's better to get something reasonably profesional, it will be working pretty hard. Any thoughts?


Depends on the volume of the airmass you need to shift. The rule o' thumb for ventilation means your exhaust blower (and intake blower, if used) needs to be able to shift the room's air in 3-5 mins. A 500cu ft room would thus need a minimum 100CFM blower. However, in practise, that's enough to supply fresh air for the plants but not generally enough to remove the heat from big lights to keep temps under 28C. 

If you have a long exhaust duct run (more than 2-3m) or a carbon filter, you'll want a centrifugal blower. Axials don't cope well pushing air into a high static pressure created by obstructions in the air path, those obstructions including a big column of air. When axials encounter more static pressure than they like, air leaks backward between the fan blades. Centrif blowers are not air compressors but they can push air lots better than an axial into high static pressure.

I use this 250mm unit as my main exhaust blower; moves 875CFM for my 500cu ft room. It's like a freaking wind tunnel. I use a couple of old 200mm axials (formerly used as exhausts in other applications) as intake blowers. Those old axials combined push about 90% of the capacity of the 250mm centrif, meaning the room remains at a slightly negative pressure. The axial intake fans are not working very hard when they are pushing into air pressure slightly lower than atmosphere. You ask, why bother with intakes, then? Simple- passive (fanless) intake is very inefficient, requires the intake opening be around double the area of the exhaust blower's annulus and thus makes light-trapping the intake difficult. 

Keeping your grow at a slightly negative pressure compared to atmosphere is important. If there are any air leaks in your room construction (and there WILL be), air will be sucked into those leaks. All air leaving your grow will go through the exhaust blower. If your room is at positive pressure compared to atmosphere, air will be pushed out of those little leaks, making scents difficult to impossible to control. 

Fletch's suggestion is OK if you can cope with scent leakage. His method will keep the room at positive pressure compared to atmosphere. If one uses an intake blower attached to the home heating system duct instead of temporarily repurposing the exhaust blower, the room would remain at negative pressure.


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## psyclone (Jan 24, 2008)

Scent leakage is ALWAYS an issue- I have no domestic problems, but I do not want to pump out Ganja-laden air out for the local youth in our Village to get excited about.
That fan looks the absolute Dogs Bollocks as we say, and I will do as you suggest and flip a couple of cheap exhaust fans as in intake (I am looking at two Medium tents, one veg, one flower) and then join the top outlets of each tent with a ducting "tee" and put the fan you recomend at the centre with some sort of scrubber.
I am assuming it's designed to be able to fit filtration?


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## Al B. Fuct (Jan 24, 2008)

Yes, centrifs are designed to push into high static pressure loads like carbon filters, etc. 

The Spectrum C250L blower I'm using does not have a flange for ducting on its intake. It has a very small lip on the intake side which _barely_ allows a 250mm duct to slip over it and be duct-taped on, but clearly, that's not the intended means of usage. 

A long duct on the intake side would produce a low pressure condition relative to atmosphere in the inlet duct. While the effect would be less pronounced in a centrif blower than with an axial, this will reduce the efficiency of the blower a bit. The vane shape in a centrif blower will almost certainly be designed to work at atmospheric pressure. Lower air pressure on the intake may cause some cavitation or stalling of the vanes.

I do have a _very_ short length of duct (about 200mm long) attached to the intake side of my exhaust to facilitate convenient mounting of the blower. I haven't put a manometer on the intake side to see how low the air pressure is in my intake side, but as short as my intake side duct is, I doubt it is significant.


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## psyclone (Jan 25, 2008)

I shall start the looking around and see what I can find in the way of importers.
Thanks for the advice.


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## Al B. Fuct (Jan 25, 2008)

Importers? For the blower? I'd shop locally for that if you're in Nth America. Remember that Aus uses 240V mains power if you order Aussie electricals.


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## psyclone (Jan 25, 2008)

Could be on Cat Island......


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