Condensing Boiler in a Brownstone -- Can I Vent Basement To Roof?

Brownstoner22

I have a 3000sq ft 4-story brownstone, need to replace 175Kbtu gas water boiler (cast iron radiators). Want to go high efficiency but my contractor is saying these need to be vented on very short runs and maybe not vertically, or they cause problems? Current boiler vents from basement all the way to the roof. He also doesn't like the reduction in water from 20 to 5 gallons due to pressure? He wants to do a Slant Fin at 84% AFUE, I was hoping to get in the mid-90s. Any thoughts would be appreciated.

Rich_49

You can vent many units up to 100' each way or a combined 200' . You can absolutely vent vertical with zero issues . You also quite probably need nothing anywhere near 175,000 BTUh , even if making hot water . Do some searching for another contractor who has a clue . You more than likely need no more than 90,000 BTUh and that is probably high for your needs . Cast iron rads do very well with lower temp water also before he hits you with that argument .

Brownstoner22

Thanks! Really helpful. I have to say he's actually a super nice guy, just old school -- and his quote for the replacement was very competitive. But I guess I should find someone who knows & likes these units.

EBEBRATT-Ed

You need to read the venting instructions for the boiler you want to install. As long as you follow the MFG venting rules you should be fine

Solid_Fuel_Man

We vent many mod/cons (high efficiency- modulating/condensing) boilers through the existing brick chimney if no other appliances will ever be connected. You need to run plastic vent up the chimney and properly terminate the top. 

Big Ed_4

I would add a trap and drain between the boiler and rise up the chimney and increase the vent size and intake ... Just thinking

JohnNY

Big Ed_4 said:

I would add a trap and drain between the boiler and rise up the chimney and increase the vent size and intake ... Just thinking

Why would you deviate from manufacturer's instructions? They give you a diameter and TDL to work with and all the HE boilers are designed to handle the condensate they produce. I've only had to drip flue piping when either over extended or an engineered change in elevation was necessary.