What do you mean by "openings"? Are you talking about soffit vents? Or crawl space? I'm confused.

The crawl space around the bottom of the house has screened openings and the original owner put steel or aluminum plate covers on the openings in the winter but the covers are missing and I am wondering whether to replace them and also where to find them.

Hmmm. Those sound like they were probably custom-made. I've never heard of something like that in my area, but maybe someone who has will chime in. Rather than :lost" I would think those nice metal plate got stacked up in someone's truck and taken to a recycler for cash.

Yes, replace them as they will help save heating costs in the winter. You can find them on-line by Googling "crawlspace vent covers."

For better efficiency, consider un-venting the crawl winter and summer and treat the crawl walls, floor and ceiling appropriately. See link.

Here is a link that might be useful: Conditioned Crawl Space Construction

I've seen thermostatically controlled crawl space vents that open in the summer and close in the winter.

Thanks for the help. I found a hardware store that carries the wrong size for about $4.75 each so now I guess I need to look around.

Thanks for the help. I found a hardware store that carries the wrong size for about $4.75 each so now I guess I need to look around.