I wonder whether I need to close my crawl space vent or not. I have three vents in different areas of the crawl space. The vents have wire net. What I mean by cover is completely closing off the vent.
Below is the image of my crawl space; there are three areas where I see vent in crawl space.
The city I live in is Everett, WA
There still isn't enough information in your post to know for sure. We don't know what specific problems or concerns you have. That said, here's some general advice.
Why you would close the vents:
Why you would leave the vents open:
In my northern region it's fairly common to close vents in the winter and open them in summer for the reasons listed. Don't expect to seek a consensus online because conditions and motivation vary. Do what makes sense for your situation.
Good news from what I can find on the web you should not be in danger of hard freezing this winter. You need ventilation in the crawl space or you will probably have mold problems. You also need to insulate the pipes if it gets much below freezing for a period of time. You could put heat tape on the pipes with a thermostat (many come with) that should keep your water running. You are losing heat through the floor which will also help keep them from freezing. Closing the vents will help keep the heat in. If it were me I would tape it, and insulate the floor if you have AC.
