Sizing for a chimney
I’m New here, so I’ll start slow. I’m replacing the heating & hot water system in my 2 family house. I have two seperate units for heating, and 2 units for hot water.
My question is:
I have an 8 inch (type B?) chimney that runs up from the 1st floor through the 2nd floor and out to roof. A total of about 15 feet end to end straight up, no 90s, but a 45 at the bottom. I need 1 95,000 BTU boiler, and 1 195,000 BTU boiler. I want to keep 1 of the old hot water tanks that’s 65,000 BTU and add a new one that’s about 40,000 BTU.
I know all this won’t fit in the existing chimney, so I’m thinking of hooking up an indirect heating tank to the boiler as an added zone, but only if I have to (too much $$$). How do I figure out how much BTU the chimney can handle? If I extend the chimney will it increase the capacity? Is there different vent pipes that I can run from the boilers to the chimney that will increase the capacity?
Thanks in advance, Hows
Welcome to Breaktime,
For gas fired appliances, 15 ft vertical rise, 395 mbh input rating total, you will need a 10" b-vent for the main vent up and out.
Individual single wall connectors for each appliance will be as follows:.
195mbh - 7", 95 mbh - 5", 65 mbh - 5", 40 mbh - 3".
This is assuming that all of the appliance are natural draft, natural gas fired and that there is a 3 ft rise for each connector to the main vent.
"How do I figure out how much BTU the chimney can handle? If I extend the chimney will it increase the capacity?"
I use the manufacturer's (Hart & Cooley) tables for b-vent sizing. Go to their website and you can download the application guide for yourself.
Vertical height increase will increase the capacity of the flue. Changing an 8" from 15' vertical only to 20' vertical only will increase the capacity from 365 mbh to 405 mbh, enough to accomodate all of you proposed appliances, but do really want an extra 5 ft of pipe sticking out of the roof?