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Old 02-14-2018, 07:20 PM #31
highsteppa
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I used to grow greenhouse hydro tomatoes and we used propane forced hot air heaters for both temp temp and humidity control. No dehumidifiers.
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Old 02-15-2018, 03:57 AM #32
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Exactly thanks.
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Old 02-16-2018, 01:38 PM #33
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Originally Posted by highsteppa View Post
I used to grow greenhouse hydro tomatoes and we used propane forced hot air heaters for both temp temp and humidity control. No dehumidifiers.
I agree. Working off of a basic VPD table, I'd use a heater to crank up the heat up to 25c, and have the RH% between 75% and 50% - depending on the growth stage of the plants in the green house.


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Old 02-16-2018, 01:43 PM #34
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[quote=brolex;8201281]I agree. Working off of a basic VPD table, I'd use a heater to crank up the heat up to 25c, and have the RH% between 75% and 50% - depending on the growth stage of the plants in the green house.

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Old 02-16-2018, 07:12 PM #35
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I have propane heat in my greenhouse. It is about 20% humidity here all summer during the day, spikes higher at night but still stays at 60-70% humidity which is fine.

Problem comes after first rain in the fall, night humidity levels hit 80-90% at night. Propane isn’t enough for me to lower my humidity at that point so I either continually run vents or dehumidify.
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Old 02-19-2018, 01:26 AM #36
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If you want to check out my greenhouse thread, i explain dehumidifying with heat in detail. I personally use pellet heat but any heat can be used as long as if it's fuel burning, it's vented.
Meaning of you are using propane or NG it is a vented unit. If it's not vented you are just adding more moisture.
Dehumidifiers are hardly ever more effective then heat dehumidification. The only time that heat dehumidification is not an option is when it's hot and humid. And the rise in temperature needed to dehumidify would put you over 90f. In that case you would want to use an ac unit to dehumidify.
That said, if you are relying on electric heat, you might as well use a dehu to create that heat as 1kw of electricity creats 1kw of heat regardless if its a 1kw space heater, 1kw dehu, or 1kw blender or toaster oven.
For every 20 degree rise in temperature humidity is cut in half.
So say it's 80%rh and 60f out. If you bring that air into the greenhouse and heat it to 80f, you now have 40% humidity in your greenhouse.
If you have good horizontal air movement, you shouldn't have problems if rh stays under 70% or so. And you shouldn't have problems if your temps stay below 90f or so.
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Old 02-19-2018, 04:12 AM #37
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Originally Posted by redlaser View Post
I have propane heat in my greenhouse. It is about 20% humidity here all summer during the day, spikes higher at night but still stays at 60-70% humidity which is fine.

Problem comes after first rain in the fall, night humidity levels hit 80-90% at night. Propane isn’t enough for me to lower my humidity at that point so I either continually run vents or dehumidify.
I am learning so much from this thread. Thanks Redlaser for the info.

What is the size of your greenhouse ?

What heater are you using ?

Do you have an idea of monthly fuel cost?

I am only planing on a summer grow looking for small plant count larger weight/plant.
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Old 02-19-2018, 04:14 AM #38
hamstring
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Originally Posted by CrushnYuba View Post
If you want to check out my greenhouse thread, i explain dehumidifying with heat in detail. I personally use pellet heat but any heat can be used as long as if it's fuel burning, it's vented.
Meaning of you are using propane or NG it is a vented unit. If it's not vented you are just adding more moisture.
Dehumidifiers are hardly ever more effective then heat dehumidification. The only time that heat dehumidification is not an option is when it's hot and humid. And the rise in temperature needed to dehumidify would put you over 90f. In that case you would want to use an ac unit to dehumidify.
That said, if you are relying on electric heat, you might as well use a dehu to create that heat as 1kw of electricity creats 1kw of heat regardless if its a 1kw space heater, 1kw dehu, or 1kw blender or toaster oven.
For every 20 degree rise in temperature humidity is cut in half.
So say it's 80%rh and 60f out. If you bring that air into the greenhouse and heat it to 80f, you now have 40% humidity in your greenhouse.
If you have good horizontal air movement, you shouldn't have problems if rh stays under 70% or so. And you shouldn't have problems if your temps stay below 90f or so.

CrushnYuba
As someone new to the GH forum I have seen your posts a few times now . Can you provide a link to your GH thread?
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Old 02-19-2018, 05:15 AM #39
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CrushnYuba
As someone new to the GH forum I have seen your posts a few times now . Can you provide a link to your GH thread?

https://www.icmag.com/ic/showthread.php?t=339175
Most of the pictures were lost. I need to run around and take replacements.
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Old 02-20-2018, 11:38 AM #40
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Originally Posted by CrushnYuba View Post
https://www.icmag.com/ic/showthread.php?t=339175
Most of the pictures were lost. I need to run around and take replacements.
reading your thread and your post in this one have been hugely inspirational while i get ready to put up my first greenhouse. here in maine we can have pretty insane humidity. luckily it stays cool enough even through summer that heat is almost always an option. one thing i cant get through my head however is how to pair the heat with intake/exhaust. if you are pulling too much cool and moist air in from outside, wont you defeat all the work the heat is doing for the RH%? I'm guessing its all about using something like half as much CFM coming in as going out? or maybe just run exhaust?
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