Thread: venting options

I currently have someone installing my water heater(gas fired) and before I let him go busting through my chimney I wanted opinions from the internet! He wants to vent it up and out about a foot from the other pipe(oil fired) all natural draft and he told me the WC was .04 was ideal so he tried to explain it to me I still didn't understand is what he is doing alright? I called my oil company and they said I could put a damper right at the bottom of the chimney and that would take care of both.

I have no idea except buy the NFPA 54 book myself and figure it out or keep calling contractors to find the answer.

Thanks.

Joe.

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Originally Posted by Joe Curtis

I currently have someone installing my water heater(gas fired) and before I let him go busting through my chimney I wanted opinions from the internet! He wants to vent it up and out about a foot from the other pipe(oil fired) all natural draft and he told me the WC was .04 was ideal so he tried to explain it to me I still didn't understand is what he is doing alright? I called my oil company and they said I could put a damper right at the bottom of the chimney and that would take care of both.

I have no idea except buy the NFPA 54 book myself and figure it out or keep calling contractors to find the answer.

Thanks.

Joe.

What is being proposed is not unusual. As long as the interior dimensions of the flue do not exceed 7 times the area of the outlet of the water heater it is acceptable. The flue should be capable of venting both appliances, meaning that it cannot be too small either. A typical acceptable liner would be an 8x8 clay tile. Make sure the flue is in good condition and that all clearances from the connector are met.
The connector for the water heater should enter the chimney above the larger furnace connector. As the gas water heater has a draft hood I would recommend installing the barometric damper on the connector for the oil-fired furnace rather than in the chimney.

Ashley Eldridge
Chimney Safety Institute of America
Director of Education
Chimney Safety Institute of America

You are allowed to common vent oil and gas appliances as long as it meets the criteria Ashley pointed out but there are additional criteria. Since you are making a change in fuels, an NFPA Level II inspection is indicated. Most likely, this will confirm the need for a listed liner.

As for the connectors, you can stagger them as Ashley stated or you can manifold them together at the chimney as long as the manifold is properly sized for both.

Another requirement is that both appliances have 'primary safety controls' such as spill switches. The code is not clear on this but the general application of a primary safety control is to shut down all burners in the event of tripping the switch. Now, you can add aftermarket spill switches to both appliances so each trips if there is sustained backdrafting while that unit is firing. The confusion comes in as to interlocking them to each other. For now, the general concensus is to just allow each appliance's safety to protect itself. However, this does no good if the safety of the appliance firing fails to trip while it backdrafts at the other appliance's relief opening such as the barometric damper or draft hood. Ideally, they should be interlocked so any spillage from either point shuts down both appliances, which would force a human to investigate the problem.

The barometric damper for the oil fired appliance should be located close to the appliance collar but at least 2 duct diameters downstream to allow a test point for combustion analysis. Any closer could result in inaccurate numbers due to insufficient mixing of flue gases.

This is a case where I would get approval from the AHJ to remove the draft hood from the WH, install a bullhead tee with a double acting barometric damper armed with spill switches to both apliances.

Don't forget to add up your input BTU ratings and calculate your makeup air requirements.

Once its all done, have a certified technician perform combustion analysis to ensure proper firing and venting.
HTH,

Joe
According to the National Gas Code See section 7.10.5 b. A listed combination gas- and oil- burning appliance shall be permitted to be connected to a single chimney flue. The chimney flue shall be sized to properly vent the appliance. The water heater flue pipe is to enter the chimney above the furnace. NO dampers are required on the water heater. NO back flow devices are required.
Now understand I do not agree with all this. I do not believe that you should vent a gas appliance into an older chimney without a metal liner.
Be sure that the installer seals the flue pipe from the water heater where the pipe enters the chimney.
Bruce Adams