I train indoors at 20 - 27 C, 35 - 50% RH.
You likely need a better blower fan. Not all fans are created equal. I’m a hobby HVAC expert.
You can’t go by “CFM” ; there is no standardized testing. I can make a fan and slap “2000 CFM” on it, and nobody can stop me.
What matters is the pressure it can create, and the actual power and volume of the airstream. The only way to know is to actually feel the differences, IRL.
Your fan should be powerful enough that you can’t look into the airstream without glasses. There should never be any drips of sweat down your body or on your bike; it should be drying on you.
[ Wearing an absorbent headband that you may need to swap a few times. ]
You should need earplugs. Not for the motor noise; for the windspeed noise. It should feel like going downhill 50 - 80 km/h outdoors.
The fan should be at head level, front-on, so that it creates a wind tunnel effect both below & into your chest, and also up over your back, simultaneously.
The Lasko Super Fan Max is currently the best fan on the market. And it’s way cheaper than so - called “trainer fans”, by cycling brands. I can only run it on speed one. Two feels like standing in a cyclone. I once did three, it removed part of my face; I have scars, never did it again.
The front exhaust grill creates 75 - 90% of the wind turbulence, and therefore noise. Theoretically, if someone used a jigsaw to cut the front grille off, just behind it, where the plastic is flat & smooth, so that the air exited smoothly, the noise of the fan would be reduced by above %. However, this would be unsafe, so don’t do it, because I definitely didn’t do that so that it is extremely quiet [ vs. the airstream produced. It’s still loud. ]
Conveniently, you can also use thin copper wire as a twist tie and attach a 6" to 4" HVAC adapter to the intake side. This can then attach to a 4" HVAC flexible hose, and slam a 4" tube to rectangular duct intake on the other end. These clip beautifully into any sliding window, etc., to intake raw cold air from outside. If & when the temps allow for that.
EDIT: Just slap a 6" to 6" cuff wired directly onto the fan. Then perma - attach the 6" to 4" adapter to the hose. Then you can pop it on and off the cuff as you like; when you don’t want the outdoor intake, the fan just sits there, w the 6" cuff attached.
[ Tape a pc of cardboard over the power outlet side of the “intake”, because it’s mostly blocked anyways; the open side supplies more than enough. ]
Earpeace Original are the most comfortable & best sounding plugs I’ve ever worn. I tested 3 - 5 brands, side by side, for noise reduction, but also sound quality. If you’ve never tried hifi plugs, you need to. They’re amazing. Wind noise can and does lead to tinnitus and hearing loss over time; nobody should ever ride at 20+ km/h without hearing protection. You’ll use them at concerts and bars too; you hear the music better than without them. Riding, you will also hear everything you want to hear, better; cars, horns, bells, ppls’ voices, etc., because the background wind noise is reduced.
Get the Pro if you want better sound, apparently. But I prefer the better noise reduction of the original. There are other brands available, I prefer these.
EDIT: Your % RH is also critical. If you’re >60 - 75 ish %, no fan can save you; you’re gonna drown & overheat. I would then 100% do a two hosed portable AC. Never buy a single hose AC.