Sharing exhaust??? Condensing Boilers

[NeubCont]

Can multiple condensing boilers be combined into one exhaust?
Have a rental house with two floors
Wanted to set up each floor with its own gas hot water heater/heat combo units
Only one wall to the exterior and it has a lot of the electrical shutoffs and panels on it.
Due to limited space in the utility/boiler room
Can this be done?
Thanx

 

[metlmunchr]

I would doubt it since these would be pressurized vents that could potentially cause a recirculation problem when one unit is firing but the other isn't. That said, the only reliable answer would have to come from the manufacturer of the boilers you intend to use. Heating codes typically include language that incorporates the manufacturer's installation instructions as a part of the code governing requirements related to the particular appliance being installed.

 

[paulsomlo]

Some manufacturers offer common venting solutions, but they're designed around a particular boiler combined with vent "ware" that the manufacturer offers to be paired with that boiler. I'm thinking I saw something on a Rinnai website recently.

 

[yeldogt]

You have to look at the specifications -- when you can it requires back flow preventers combined to a larger common flue pipe and proper transition to that pipe. Often a safety bypass in the larger flue. Strict pipe length limits.

Condensing boilers have a fan -- this is a positive pressure point. You can't have one fighting another .... or back flowing when only one is running. Often they use 2" and 3" flue pipe and most can't pressurize a larger flue to properly exhaust.

 

[BD1]

Definitely contact manufacture.
I would say No because of pressure switches.


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[fitter30]

No

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[LS6 Tommy]

Nope. Gotta have neutralizers on the condensate drains, too. They need to be replaced or refilled yearly.

Tommy

 

[paulsomlo]

https://www.rinnai.us/system/files/2018-02/z6o0udahaytsae3u6fc0.pdf

 

[brewchief]

There are some units that can be common vented but they are generally units designed to be connected together to increase capacity.

How much room do you have for vents? There are usually multiple vent termination options, some need more space then others.

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[yeldogt]

Those saying "no" are not correct .... there are many situations where this is the ideal solution.

Just follow the manufacturer specifications.

It's the same with any venting ... some units can have very long distance vents -- others require short distance. It's all in the manuals ...most manufacturers have a specific manual for venting.

Some of the on-demand water heaters have limited options in the less expensive units ... the OP is doing a combo and they are typically higher BTU and have options

 

[danski0224]

Can multiple condensing boilers be combined into one exhaust?
Have a rental house with two floors
Wanted to set up each floor with its own gas hot water heater/heat combo units
Only one wall to the exterior and it has a lot of the electrical shutoffs and panels on it.
Due to limited space in the utility/boiler room
Can this be done?
Thanx

Choose a piece of equipment, then read the venting section in the instructions.

Repeat as necessary.

 

[LS6 Tommy]

Those saying "no" are not correct .... there are many situations where this is the ideal solution.

Just follow the manufacturer specifications.

You cannot have gas fired appliances on different floors of a building share a stack. Its a flat out "No".

"2012 IMC
801.19 Multistory prohibited.
Common venting systems for
appliances located on more than one floor level shall be prohibited,
except where all of the appliances served by the common
vent are located in rooms or spaces that are accessed
only from the outdoors. The appliance enclosures shall not communicate with the occupiable areas of the building."



Tommy

 

[brewchief]

You cannot have gas fired appliances on different floors of a building share a stack. Its a flat out "No".

"2012 IMC
801.19 Multistory prohibited.
Common venting systems for
appliances located on more than one floor level shall be prohibited,
except where all of the appliances served by the common
vent are located in rooms or spaces that are accessed
only from the outdoors. The appliance enclosures shall not communicate with the occupiable areas of the building."



Tommy

I read it as he has two boilers in a shared mechanical room or basement.
It may be difficult to find equipment that can be common vented when not sharing the same load. A lot of the equipment that is designed to be common vented is designed to be part of a cascade system, you might use 3 400k boilers to take the place of a single 1.2 million btu unit, as load increases more boilers are brought online to handle it.

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[LS6 Tommy]

I read it as he has two boilers in a shared mechanical room or basement.

Ahh! I get it. I saw "Wanted to set up each floor with its own gas hot water heater/heat combo units" and was thinking on on each floor.

Tommy