Common BigMaxx exhaust pipe spec?

[themeatsweats]

Hi all. I searched and read through a bunch of exhaust pipe (horizontal vs vertical) threads, but didn't see any pertaining to tying into an existing pipe. I've got a water heater closet right next to where the 50k BigMaxx is mounted and have been agonizing over whether I should do a horizontal or vertical duct. Now to further paralyze me, I'm considering tying into the existing water heater exhaust.

Far as I can tell, it appears to be 3" all the way up. Pics show it through the garage ceiling, takes a couple 45s and then exits through the roof. Is it possible to tie my heater into this pipe and save myself a roof penetration? The only mention of common exhaust in the manual just states that it can't be used in a horizontal fashion. Is there a spec on how many BTUs a 3" duct can support?

 

[themeatsweats]

Just found this in the manual, but I am taking everything I see in here with a grain of salt since they also recommend b-vent and a vertical raincap for a horizontal application

 

[toyotadriver]

I have a propane water heater and a propane Mr. Heater (45K-it's an older one....newer ones are 50K) vented together. The common vent is 4 inch. The Mr. Heater and the water heater are both 3 inch vents. The vent exits the house vertically through the roof. The Mr. Heater has a 90* pipe and then straight into the 4 inch pipe and straight up. The water heater goes up vertically, 45* pipe, then into the 4 inch wye pipe and up and out. Been working great for 7 years now.


Nothing in this post should be misunderstood, interpreted, misinterpreted, or construed to be of a political nature.

 

[D45]

Heaters up to 75k can use a 3" vent

 

[PCustoms]

I'm 99% sure you cannot combine vents.

I might be wrong, but at least being wrong this way won't kill anyone.

 

[brewchief]

3" B vent is barely adequate for a single water heater, common vent charts don't even show 3", they start at 4". In order to calculate the needed size you need the vent height from the appliance outlet to the roof termination, the btu input and type of appliance (fan assisted or natural draft) the amount of offset in the common vent, the lateral length of the vent connector.

This looks to be a case that it will be far easier to run a new separate vent.

 

[themeatsweats]

3" B vent is barely adequate for a single water heater, common vent charts don't even show 3", they start at 4". In order to calculate the needed size you need the vent height from the appliance outlet to the roof termination, the btu input and type of appliance (fan assisted or natural draft) the amount of offset in the common vent, the lateral length of the vent connector.

This looks to be a case that it will be far easier to run a new separate vent.

Looks that way. If I've done my homework, it looks like my options are vertical b-vent through the attic/roof for $120 from Lowes, or stainless through the wall for about $300. The manual shows horizontal b-vent, but I'd rather not have to replace it in 5 years. Does all that sound about right?

 

[brewchief]

Sounds right, horizontal B vent is no longer allowed where I'm at so it's stainless if sidewall vented. Ive yet to see a thimble for a sidewall vent that looks decent and doesn't need a bunch of silicone to seal to the sideing and most of the time you end up with a long piece sticking out to clear a soffit so it looks sore. I greatly prefer a vertical vent through the roof and will only do sidewall if there is no path to go up or the roof is something we don't want to cut through(slate, wood shakes, tile, etc).

 

[themeatsweats]

New 4" vert it is. You're a legend, brewchief. Thank you