MH and Heat - turning my tank into soup cooking pot?

[andsoitgoes]

The house we're in has horrible insulation and my wife and I must just produce a LOT of heat

I have no cover on my tank, previously did have a glass top, but took that off as soon as I got the legs.

No sump yet, but am putting in one in the next few weeks.

I have 4 powerheads (I know this isn't helping the situation) - and I struggle with getting ample flow to the right places. I have 1 PS 20, 1 AC 301, and 1 coraline covered u/k powerhead

There's no computer in the room, there are another 5 tanks nearby, the one below (my Freshwater planted) is a cool 75, and the tanks to the left are all running below 80. There's the standard Aqualight Pro fan installed on the light as well.

Heat register is covered in the room (magnetic cover)

I figured a 1/10 was too much, can't seem to find a 1/5 anywhere, but that's why I'm starting now.

Just wondering if the sump will answer a lot of the problems, but my initial goal is to do a refugium w/ skimmer above as my tank isn't drilled - hoping that won't cause more problems than it's worth.