Fuel Oil and Gas

[Bugster]

I apologize if this is the wrong thread, but its the closest for my question. Are there any codes for the sharing of a fuel oil boiller flue and LP boiler flue within the same stack? Both flues go above roof line, but share the same rain cap. The LP is primary and fuel oil is back-up only. Any verification from NFPA or ASHREA would be helpful.

Thank you,

[hearthman]

NFPA 211 and the 2009 IRC both allow common venting or interconnection between gas and oil. Solid fuel must have its own separate flue.

You refer to same 'stack', which is confusing. They appear to share the same flue. Are there two separate flues within this one chimney-one for the oil and one for the LPG but both terminating under one large multi-flue cover?

Those connectors look pretty big. A common vent or flue must be sized for the combined BTUs. Both appliances must have primary safety controls. Both have very little vent rise. I don't see a listed liner but I do see galvanized steel cemented into the wall which is not approved in 211.

I would install a listed liner sized both both appliances and bring it in closer to the ceiling while maintaining clearances to combustibles. You would use type L vent near the ceiling for a 9" clearance to combustibles, manifold it, install separate barometric dampers with spill switches, etc.

Any pics of the top of the chimney?

Move this to Pro section and we can discuss sizing and other details.

[meplumber]

This looks like a commercial or institutional installation. If that is the case, there may be other codes or standards that come into play by municipality and state.

What is the building's usage?

[Bugster]

Hearthman and Meplumber,
Thanks for your timely responses. I will post a couple more photos for referencing; though crude.. they may assist with increased defining of use. The heating water is used for a large garage with docking access.

[Bugster]

Here are a couple more photos of installation;

[hearthman]

You have a problem there with that draft inducer/ power venter. It can generate positive vent pressure, which is not allowed in either vent system. Positive vent pressure can only be on one appliance regardless of fuel type and the venting must be listed for positive vent pressure. Just gooping joints with red RTV silicone does not count. Besides, in this application, it could easily vent from the WH back through the boiler into the room if the top of the chimney is blocked.

Do you have a photo of the chimney taken from this county? A little far away...

[pacnw]

You have a problem there with that draft inducer/ power venter. It can generate positive vent pressure, which is not allowed in either vent system. Positive vent pressure can only be on one appliance regardless of fuel type and the venting must be listed for positive vent pressure. Just gooping joints with red RTV silicone does not count. Besides, in this application, it could easily vent from the WH back through the boiler into the room if the top of the chimney is blocked.

Do you have a photo of the chimney taken from this county? A little far away...

not to hijack, but a similar question/situation;

a NG natural draft H2O heater with an Iron Fireman oil furnace. Is the I.F. considered a power venter or induced draft and therefore okay? I have questioned this for years, have 3 homes this way of which 2 are former company owners homes.

[hearthman]

PAC, your answer is not from the mfrs. propaganda but your manometer. If you read positive pressure in the vent connector, then you must treat it that way. This is under 'steady state' (as if that truly exists) or after 5-10 min. of firing.

Note in the pic all the red RTV downstream of the inducer/ blower. Shouldn't be needed if nat. draft. If it truly just induces and vent pressure goes neg. then its ok for a minute or so......unless its dumping gobs of CO into the CAZ.

[meplumber]

pac. The I.F. oil furnace is not positive draft. At least I have never seen one that was. As long as the flue is of the appropriate size and the smaller btu appliance (the water heater) connects to the chimney above the larger, then you are alright.