Air combustion vent, ducts and in-line fan size?

[Brianosaur]

I need to add a low mount air combustion vent and a high mount air exchange vent, both to the outside, in my enclosed oil fired boiler utility closet.

The spec stickers on the Peerless boiler state the max at 129k btu's.

If I need 1"sq/2000btu's for horizontal duct that would be a 65sq in.
8"x8" or 10" round.

If possible, I would instead like to add a 4" round with an in-line duct fan to save what little space I have.

How would I convert the additional cfu's from the fan into the amount of square inches I need and know what size cfu fan to get?

 

[Dana]

Pressurizing the boiler room relative to the rest of the house using a fan is bad idea on a number of fronts, don't go there.

Many codes now require a square inch per 1000 BTU, not half that, a result of houses being built tighter in the post IRC 2009 era.

Odds are much better than 50/50 that the 129K-in /110K-out boiler is more than 2x oversized for your actual heating load, and down-firing with a smaller nozzle would likely provide higher comfort & efficiency.