I’m not trying to say or suggest that. If I read correctly above (and certainly possible I didn’t) I think you said your rh in the lung room is pretty consistent at 75% rh.
Let’s assume you can maintain the inside of your flower tent at that same 75% rh (highly unlikely, but we’ll assume).
What does your vpd chart show the required temp to be at 75% rh for late flower?
It’s not a test 
, I’m curious. I’m thinking you’d need to be 100f+ to get 1+ vpd
The chart I have that i linked above does not specify stage of growth, so I assumed that that same VPD applied at all stages?
Maybe I dont undersand the chart right? As I was reading it, if you look at 75% rh at the top, It goes yellow, which I assumed meant a okay temp, to green which i took to mean a good window of temp and back to yellow which as above I thought meant ok but not great. Red I assumed was bad. so going by that chart with the way i was reading it I thought at 75%Rh I was at least ok from 59f all the way to 93.2F. Am I reading it wrong? I am very new to VPD never needed it for food plants outside or in my first grow tent indoors.
I think the Pulse charts are fairly well accepted and sure read easier than the one you have. This one suggests in late flower you need a leaf temp of 100+f to maintain proper vpd at 75% rh.
Yeah, looking at your chart, I’m just not sure. Your theory of chart reading (seems logical 
) would suggest that at 75% rh, any temp between 65f and 90f would land in the “acceptable” vpd zone, but that’s just factually incorrect, so I’m not sure what they are trying to say. There’s no growers here who would agree with that….
Maybe take a look at those Pulse charts (there are different charts for stages of growth) and see if that makes more sense.
You can successfully harvest big colas with your tent rh in the 60’s %, but it can get dodgy and does require some experience. 50%’s is much much better. 70’s is just asking for mold/rot in my experience.
Looking at your chart, Wouldnt I be OK if the temp in the tent was at least 82F? That is where yellow starts if I am reading it right anyway?
There are different levels for seedling, veg and Flower. Much easier to see if you use a laptop.
These are not be all end all but a nice target to shoot for based on environment ability.
Im on a desktop pc. But I guess I am not understanding the chart, cause the way it reads to me, In flower stage, i would be “okay” as long as it was 82f or higher. So not sure if im reading it wrong or not. I can say that i highly doubt ill ever be able to afford everything to hit “the perfect vpd”.
The yellow area of the chart that you are interpreting as “okay” is actually the caution zone. At the 82f level, with 75% rh, in flower, you are on the edge of caution vs danger. That’s just really not an area that most of us choose to live in. Try to get into the light green area as a minimum.
Agree, nothing is ever perfect, nor does it necessarily need to be.
We are talking specifics and you are still a ways away, so let’s not get bogged down. I’ll just go back to my original comment that your 75% rh is going to be an issue when you start flowering plants, and you should start considering that, and a $40 in-tent dehumidifier isn’t going to solve the issue.
Good luck, let me know if I can help!
And edit to add, I’m throwing all of this vpd stuff out there, and, tbh, I don’t pay too much attention to that specific metric. I’m a temp/rh guy myself, I have just learned what works through trial and lotsa error.
i had no clue about VPD till reading this i think, but i dont think such a table does realisticially reflect the conditions in a growing tent. Its probably useful as a guideline thou.
The humidity, temp and air flow is vastly fluctuating from area to area inside a tent. You might measure the correct values at the bottom, but over by that branch it will be different.
Then the plants themselves will be vastly different, even amongst relatives, their size and the amount of water they moves are different. Mind fluctuations due to night and climate madness, nutris and whatnot.
Better airflow helps alot here.
But then we also have to consider that ganja is different to most vegetables or fruits and berries and so on, as that they have dense buds, with lots of irregular cavities for moisture to rest in. We rarely measure in there thou, hence have to judge from the overall tent climate to how the buds are doing inside.
This, i presume, results in many people reporting those low RH and temp numbers being preferable, its like a safetycap to cover the uncertainty.
found a reasonable 3000sq ft dehumidifier, that I think I can squeese into the budget. the room the tent is goin in will be a 3021sq ft room so I think that should be close enough.
Sounds like a plan. That’s a big room!
its a 12x20 foot room. Should I put the dehumidifier in the lung room or in the tent itself? If im looking at the charts right, I should have to drop the RH to about 60% to hit the green zone for flower. Shouldnt have a problem hitting a 15% Rh drop or at least I hope its not lol
If it’s rated for 3000 sq ft, you should put it in your lung room. That’s basically a whole house unit, which is exactly what you are gonna need. It’ll only run as necessary, so don’t worry - oversized is better. You just need to be sure you’ve got a good exhaust system for the tent.
I’m not even going to make you worry about the fact that the dehumidifier is going to throw out a lot of heat, increasing the temp of your lung room. 
It’s always something…
Your first run in new tent, you are going to discover the problems.
Second run, you’ll fix a bunch of issues and it’ll be better.
Third time, you should have an idea of how your environment behaves and what it takes to control it. It’ll get a lot better from that point on.
