*
I am renovating a 3 family home. I would like to vent a gas hot water boiler (175,000 btus/82% efficient)and 3 gas hot water heaters (32,000 btus each) into one large chimney stack. What size must the flu be to safely vent this equipment?
Any comments are appreciated. Thank you.
Replies
*
It depends... Definitely a question for a pro. Too large and too small can get you into serious trouble.
*As andrew says: it depends.You need to know the Total Vent Height and then use your BTUH input to determine the Minimum Internal Area of Chimney.Example:275K BTUH input @ 10' Total Vent Height = 78 square inches minimum internal area.275K BTUH input @ 30' Total Vent Height = 50 square inches minimum internal area.Hope this gives you some type of an idea.
*Does your code, or for that matter, your inspector, allow multiple appliances to be vented into a single flue?Even though my code allows it in certain cases, my inspector chooses to have a separate flue for each appliance, even if they use the same fuel. He holds fast up to 3 flues, then he'll allow two like-fuel appliances to share a common flue. Lots of variables thrown into the (his) equation, though.If you can vent all four gas appliances into a single flue, would it be prudent to install two flues just in case the owner someday decides to install an appliance that burns a different fuel? Possibly uneccessary, but less expensive and easier to do it now then in the future. Just a thought.
*Our furnace has a bunch of scary multivariate tables, accounting for factors such as min/max BTU input, vent height, diameter of connecting flues, height change of connecting flues, etc. in calculating the main flue diameter. And this is for sharing a flue with ONE water heater. The furnace has a fan to ensure a draft up the flue, which tends to make natural draft devices such as a water heater backdraft. Basically, the amount of backdrafting too small to care about. But there are a lot of rules of thumb in play here, more than are worth tinkering with when an HVAC pro could give you the right number for your jurisdiction in ten minutes.
*Fred, He (inspector)used to live up in Alaska. His wife and daughter were hit with CO poisoning (BTW, not his house, they were visiting friends). Daughter died, wife was in a coma for several years 'til she passed. Thus, he has a few quirks when it comes to fire safety and CO. He inspects two of the towns I build in. Different inspectors for the other towns, they essentially go with basic code. It's been debated down here, as it is a bit more expensive to throw up a multi-flue chimney. We've got a few meetings coming up, we'll see where they lead. As for him being a "nut" I'll throw out this statistical tidbit from one of our last meetings:Our town, as well as the surrounding towns, keep records of all emergency responses made by the local fire departments. For the two towns this inspector "controls", responses for high CO levels (homeowners calling in or monitored alarm generated responses) are 43% less than in the surrounding towns. That number takes into consideration certain new home construction rates and variables, etc, and is adjusted for differences in population.Fluke? Who knows. Is the added expense worth it? Who knows. BTW, I enjoyed your article in the last issue of FHB. Nice job. Mongo
*A grisly education. His solution may or may not be right... But I remember a family outside Boston dying because the exhaust on their driveway heater (for people who don't like to shovel snow) was plugged up with leaves and the poisons backed up into the house. Awful.I can't see the harm in combining natural-draft appliances at least. But a lot of other variables are important. I was in a seaside town in Calif. recently, a valley town that i guess gets a lot of winds, and every chimney had a weathervane-style attachment to the top of the flue, designed I supposed to keep the orifice downwind at all times. I'd never seen anything like it.I'll be triple-checking our new flue. Sealed combustion is sounding better and better. Or put the damn equipment in a shed out back.
* Mongo,
Joseph Fusco View Image
*
I am renovating a 3 family home. I would like to vent a gas hot water boiler (175,000 btus/82% efficient)and 3 gas hot water heaters (32,000 btus each) into one large chimney stack. What size must the flu be to safely vent this equipment?
Any comments are appreciated. Thank you.