Unused fireplace has been sealed. Do I need to vent it? If so how?

bflare

I moved into my new home in March & when it was raining I could hear dripping near the unused fireplace. On inspection, the previous owners have screwed a board into the opening with silicone around it. The chimney pot also still had a revolving spinning cowl which I am assuming was allowing rain to get into the chimney. The house was built in 1984 & is the only house in the street with a chimney. The breast is quite a nice feature & I am wondering whether the previous owners had the chimney added & maybe a wood burner at some point? 

I have now removed the Rotorvent Spinning Cowl & replaced it with a rain cap which still allows for some ventilation. However, I am now left wondering how to vent the bottom.




Can I just add some kind of vent to the board? I have not taken the board off but I have removed some of the silicone, unscrewed the screws & let the board drop slightly & you can see quite a lot of s@it laying on top of the board. You can also feel a draft so air is getting through. I am reluctant to remove the board as I have no idea what's under there including the possibility of spiders!

Any suggestions?

FreeBear

Looks like a register plate before a hole is drilled for a stove flue. If you don't plan on putting a new stove in, I'd seal the plate back in place and then drill a couple of holes through from the outside into the flue. A couple of 25mm diameter holes will be more than enough. Fit a grill over the holes after they have been drilled, just to neaten up the wall.

Putting the ventilation holes on the outside will prevent the spiders from coming inside.