Just surprised a residential unit (I have a 50 pt in my basement for comparison) can generate enough heat to heat such a big enclosure.
I'm working on making a much smaller kiln (3'x3'x10') that will be serviced by a 25 pt dehumidifier. I'm guessing I'll need a way to introduce outside air if the inside gets too warm?
This box will be 7x7x10=490 cubic ft last box was 5x6x12-360 cubic ft This will be better insulated. Face 12x6 of kiln 1 were 1/2 plywood with 1" foam screwed on. in the beginning it was sorta sealed, in the end, it had taken a beating from miss steps with tractor. I was still venting in October-Nov. and in spring. I do not use in summer. I would need an AC unit.
I like to keep green burl in the 80-90 degree range for the first 2 weeks. after that 100-110 is ok.
I assume with tighter box-more insulation, smaller door area and much better sealing and insulated doors that the 75 will need venting. the 50 did.
If your box -90 cubic feet is insulated and sealed I would assume you will definitely need a vent.
I have only had the one kiln. but learned a lot using it.
1. there is a LOT of water in fresh cut wood.
2. if you keep temps low enough in beginning it is very hard to screw things up.
3. Just because water stops coming out does not mean dehumidifier is dead. Usually it means wood is dry. This lesson is why I have 2 working dehumidifiers.

4. I have used kiln for other things but most of my experience is with burl. Mostly maple burl but also box elder burl. I think burl is a much different animal than regular lumber.
5. also have to remember, I have read up on kilns and drying cycles, Etc. I go by none of this. I operate on what works for me nothing else. Why fix what is not broke.
Took me about 5-6 weeks to dry maple burl in last kiln. this one will have 2 sets of rollers on floor and the burl will be 2 stacks high-rolled in and another 2 stacks will go in. so I probably will have 1/3 + more burl in there. I expect results to be about the same. We will see.