[VegGrower]

I've started seeds indoors, under lights, for years. I am fortunate to have enough space in my boiler room, so no heating cost and the LED light is consistent / predictable - unlike heating a greenhouse! and sun light quality in Spring being very variable

Problem is that the bugs love the environment too.

I was wondering about enclosing the growing rack with a cover, and a fan (and filter) with positive air pressure in the hope that would prevent the bugs getting in there easily.

I Googled it - it seems that most indoor growers (with high value crops ) want negative air pressure so no smells escape ... and I couldn't find much about positive pressure.

I wonder if I open the side to water whether the bugs will get in and, of course, once in and multiplying the fact no new ones can get in won't make any difference.

So would it be a waste of money? or have I got to get a white coat and a hair net to do the watering?!

[AndyRVTR]

The bugs (or lavae) will already be in your compost, the larvae will hatch when your compost warms up releasing the little black flies. I now blitz my compost in the microwave for a few minutes allowing it to cool down before using it, no flies on me now! 

[VegGrower]

Thanks, sorry wasn't clear. I agree with you that microwaving compost to kill any fungus gnats helps; I don't tend to have a problem with them (I'm using commercial-grade compost, maybe that helps). The things that invade my indoor growing room seedlings are aphids and the like - basically the ideal growing conditions also suit the aphid perfectly

[Hortic]

Bugs? What kind of bugs? If they are tiny little flies these are fungus gnats and will come from the compost. (It's a problem with peat free the manufacturers haven't got a grip with yet.) I water/use a spray of permethrim to kill them off, repeated required as they hatch at different rates. Don't over water as this encourages fungus gnats.
The smell you mention comes from cannabis farms, not veg growing.