My friend has the deadband on his AC setup to 3 degrees so his AC comes on fairly often. I've read that a lot of on/off intervals is not good for the compressor and is not very efficient. I was also thinking of combining AC with venting to cool the room very quickly but also have the deadband set fairly high, like 10 - 15 degrees (see Grow journal in signature for details). This way the room would cool down from like 85 to 70 or something like that. That way when the cooling period ends the CHHC-1 controller would blast the room with CO2 until it gets back up to 1500 ppm and the plants will have a longer CO2 uptake period before the next cooling period begins. This would also be a bit more efficient for the AC and easier on the compressor. (I will be upgrading to a mini split AC after I have a couple grows under my belt.) So the questions after the long explanation: is a 15 degree temp change considered dramatic? Would it adversely affect plant growth?

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This might help you but keep in mind that this speaks to internode control:

Temperature control

The easiest and most under-used way to control internodal stretch is temperature control. Plant internodal length is directly related to the difference between day and night temperatures – the warmer your day cycle is as compared to your night cycle, the greater your internode length will be. The opposite also holds true; the closer your day and night temperatures, the shorter your internodes will be. Ever notice how as the warmer summer months approach, your plants begin to stretch? Part of this problem may lie in an overall hotter grow-room, but a larger factor is the increased difference between day and night temperatures.

Lets look at putting this to play in your grow room. Maximum temperatures should ideally never rise above 26°C, so you must do everything you can to prevent your room getting too hot (run lights at night, use exhaust fans, air conditioners, etc). An ideal temperature range is 24-25°C when the lights are on, and 22°C when the lights are off.

The temperature technique is most effective under a 12/12 light regime, which is ideal as this is when cannabis stretches the most. When the light cycle is brought to 12/12 we will raise the night temperature to the daytime level of 24-25°C. Space heaters on timers work well for this, and max/min type thermometers are ideal for
tracking temperatures.

It is during the first 2-3 weeks of the flower cycle that most strains begin to lengthen internodes, making it a very important time to control temperature, as this is when the framework for future colas is built. After this 2-3 week window we need to drop the night temperature back down to 22°C, as this is where the plant is happiest.


As floral development begins we need to keep in mind that the total size of your buds is determined largely by average daily temperature, provided it does not exceed optimal. So if you are letting your day temperatures drop below 24°C or your night drop below 22°C, you are costing yourself in overall weight and harvest.

Once your buds have reached optimal size and and you have begun the flushing period, you may consider dropping temperature down to 17-19°C for the final week or two. This drop in temperature triggers anthocyanin production, which intensifies the colour of the floral clusters and makes for a showier bud, especially with "purple" varieties. This final temperature change is not always feasible and can be omitted.

For extreme height control you may even use warmer night temperature than day, but be very careful when running settings like this, as even a zero difference between night and day temperatures will lead to leaf chlorosis (yellowing) after 2-3 weeks.

Some things you will notice while using this technique are a change in the leaf angle, upwards during warm days and downwards during warm nights. There is also the chlorosis if this is done for too long. Neither of these symptoms is nutrient related and will fix themselves when the temperature is changed back.

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Most residential thermostats don't have an adjustable deadband and in fact 3 degrees is pretty much standard.

Yes...you are correct. Starting a motor (or compressor) is not as efficient as running it. We're talking pennies though unless it's starting up every 2 minutes. And....naturally it does cause more wear on the motors with "short cycling".

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Thanks gohydro. That is very interesting. Where did you get it from? It doesn't exactly address temp changes with a given day (lights on period) which is really what I'm looking for. Good lookin out though.

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The default temp deadband on the CHHC-1 is 3 degrees as well. More than the AC issue I'm more interested in allowing for longer CO2 uptake periods with shorter cooling/venting periods.

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Been growing for over 25 years and I found it somewhere a long time ago.....cant remember where but it is invaluable to indoor growers who struggle with height issues. Heres my current grow at 23 days (one of the last posts)


Hash Plant in NFT system

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anyone else have any info on temperature variation during lights on and plant growth?

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I shoot for a 10 deg. change. That what I was told many times. Don't know why.

You mean a 10 degree change during cooling or a 10 degree difference between lights on and lights off?

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that would lights on and off.