Oversized overtall chimney?

captainco

I was on a job once with a contractor and it took opening a double garage door to overcome the leakage of a house. We didn't tell the homeowner to fix his house or tell him his chimney was too big for his orphaned water heater. Excessive house leakage causes down drafting not excessive up drafting.

Wet chimneys loose about 40% of their capacity when wet, which is why caps are called rain caps.

Open door, cold and wet chimney and door open. Which way will the air move initially.

There is not one scientific study that proves chimneys can be too big. I can come up with hundreds of field situations where big chimneys were never the problem. Pressure and temperature control chimneys not size.

Bob Harper

Install a smoothwall 316 ss chimney liner sized for the input rate. Incorporate a barometric damper and set it using a draft gauge btw the baro. and the flue. Seal the upper level air leaks in the home. Run combustion analysis to tune the burner.

A manual fixed blade stack damper is a flow obstruction. BTW the barometric damper and the burner compartment, it can cause sufficient flow disruption to cause flame impingement, which leads to CO production and soot. Use with caution and only guided by testing.

Too high draft pressure can cause CO production so it must be regulated and the only thing that does that reliably is the baro. damper properly set. In extreme cases you may need to install a baro. larger than the vent connector diameter or add a second. On gas, you would use double acting baros. with spill switches attached.

Jamie Hall

Really now. You are going to use a fan to bring in more air… in hopes that a little less air will come through the cracks? Please…