Crawl space vent to outside - can I seal it?


I pulled up the floor to the crawl space just in the back part of the house to put black plastic down and insulate it and I found a one foot square hole to the outside and the air coming in is FREEZING. There is a half basement with a small window and another small vent about 7 inches in diameter under another room next to the big freezing one. The house was build in 1900.
Can I seal up that airspace or put insulation over it? It also has a grating outside on the ground and I bet when it is raining that water gets in too.
What are my options? Thank you
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it may provide fresh air required for combustion in heating.
Mulan wrote:

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the vent is to allow moisture to leave, and dirt tends to become moist on the other hand, there are people who argue that crawlspace vents should be sealed and moisture problem handled with sump pump. in fact there are companies whose business is to seal up your crawlspace
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peter wrote:

How in the world do you handle crawl space humidity with a sump pump? Wait till there is 6 inchs of water, then pump it out?
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What I've always done is; cover them after the first frost & open them up after the final thaw. I may misjudge the final thaw, but this isn't rocket science, I may even wait till it hits 80 degrees out. I bought some automatic vents that have a bi-metal spring to open & close them at a set temperature. I haven't installed them yet, but they will free up 5 minutes a year.
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Close it in winter open it in summer, plastic on the ground will help keep humidity down. A house built that long ago is not sealed well anyway .
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As ventilation is generally a good thing, perhaps put fiberglass bats on the underside of the floor over the crawl space. Then the cold (fresh) air in the crawl space won't chill the floor so badly.
Mulan wrote:

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Mulan wrote:

If you have any dirt still showing in your crawlspace/basement. Cover it with 4-6 mil plastic. Make sure that you have 2-3 foot overlaps so that any water that gets in can drain to the ground through the overlaps.
Yes, seal the whole thing up in the winter. Plug every hole and opening with fiberglass insulation and cover the outside of holes with wood to keep the fiberglass dry. I would add something over the window too unless you use if for illumination, in which case, I would cover with 4 mil plastic in the winter. You can remove the insulation from the big areas and replace with screens in the summer.
Don't understand about the grill on the ground and water coming in. Water should drain away from the foundation/basement walls.
A 1900 era house is so leaky that you shouldn't need to worry about air for combustion of a furnace. If a furnace guy says you need more air, then run a cold air pipe from outside to the furnace and put a damper on the pipe (opens when the furnace draws combustion air).
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