My 80+ year old house is about 80% over a 2.5'+ high crawlspace with block walls, with a small interior basement. On the SW side I have a removable solid entry door (pt lumber with insulated back). On the SE side I have an approximately 1.5x2' window that's rusted just a little bit open and won't budge. On all sides I have 1-2 (each side) apprx 12" x 4" oval openings in the block that have metal grates in the back, but that are curretly closed up with pieces of 1" thick foamboard that I cut to fit to reduce drafts under the house in the winter. I just had a central heat/air system put in, so I have insulated ductwork running through the crawlspace. I have plastic on the ground and insulation under the floors in the crawlspace. There is no insulation on the walls of the crawlspace.

I just don't know what's the right thing to do for the summer. Do I open up and ventilate the crawlspace as much as I can or keep it closed?? I'm presuming that since it's not a conditioned space, that I should give it as much ventilation as possible in the summer, including possibly replacing the door with a grate and finding a way to open that window, to keep down mold and mildew. But I keep reading other things that say I should keep it locked up tight which doesn't really make sense to me for an unconditioned space but I'm not going to pretend that I know what I'm doing.

So, can anyone explain whether I should try to keep it closed up, or if I should open up just the oval vent holes, or if I should try to keep it as open and ventilated as I can?

Thanks!

However, before attempting any changes he advises: "Be sure to consult local experts and code officials before attempting unvented attics or crawl spaces on your own."