Gas water heater/oil fired furnace sharing flue

[msteger]

I was always under the understanding that gas fired appliances can not share a chimney flue with oil fired appliances. In my particular case, I am talking about a gas fired water heater and oil fired furnace venting into an unlined chimney. The two metal vents entered the chimney adjacent to each other (one above the other).

The JLC field guide (volume 2 page187) says no, as well, but the national fuel gas code says this is Ok.

JLC - "Never vent gas burners along with oil or solid fuel appliances in the same flue."

2006 INTERNATIONAL FUEL GAS CODE® CHIMNEYS AND VENTS -

"503.5.7.4 Combination gas- and oil fuel-burning appliances. A listed combination gas- and oil fuel-burning appliance shall be permitted to be connected to a single chimney flue. The chimney flue shall be sized to properly vent the appliance."

If I look at both (the JLC book and IFGC), they contradict each other. Which one is correct?

I've attached a photo. Oil fired furnace is the lower vent; gas fired water heater is the top one.

Is this type of installation Ok (assuming a proper flue liner) or not?

Thanks.

Image Insert:

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[Bill Kibbel]

I was always under the understanding that gas fired appliances can not share a chimney flue with oil fired appliances.

I hear that quite frequently. I'm pretty sure that's a myth. It's permitted if the flue is the correct size and appropriate material for both appliances.

That being said, I find that mixing gas/LP and oil eats up terra cotta flue tiles very quickly.

In my particular case, I am talking about a gas fired water heater and oil fired furnace venting into an unlined chimney.

That's different. It needs a liner whether it's for gas, oil or both combined.

[Neal Lewis]

Matthew,

Oil and gas is OK in the same flue. The solid fuel is not OK.

Looks like there are clearance issues for both of the metal vents.

[Jim Morrison]

The smokepipe from the water heater should enter the flue above, as it does in your photo. Clearly the flue should be lined, but assuming a properly sized and intact flue liner, there's nothing wrong with that arrangement.

[msteger]

Thanks for the help guys on this one.

So, if one appliance is fuel oil and one is natural gas, they can share the flue but the gas one needs to be on top of the oil one. Side by side for this example arrangement is NOT OK, correct?

[Bill Kibbel]

Originally posted by msteger

So, if one appliance is fuel oil and one is natural gas, they can share the flue but the gas one needs to be on top of the oil one. Side by side for this example arrangement is NOT OK, correct?

It's not the fuel, It's the size - smallest is always on top.

Originally posted by Jim Morrison

The smokepipe from the water heater should enter the flue above, as it does in your photo.

I've spent a good bit of time in and around Boston. Enough to pick up things like "wicked-good lobsta" and "bang-a-youie", but WTF is with "smokepipe".

[hausdok]

Originally posted by inspecthistoric

I've spent a good bit of time in and around Boston. Enough to pick up things like "wicked-good lobsta" and "bang-a-youie", but WTF is with "smokepipe".

That's funny,

I call 'em smoke pipes out here too and I grew up calling 'em smoke pipes.

Bill's led a sheltered life in them thar Pennsylvania hills.

OT - OF!!!

M.

[randynavarro]

I just finished a 2 day oil and gas seminar a few weeks back and the 74 year old instructor called them smoke pipes as well.

Back to the original question: I'm not sure anyone has reconciled the JLC Field Guide statement condemning mixing oil and gas together. Might this be folklore as well?

[hausdok]

Well,

I'm not sure. The way that I read that code, they're talking about a combination fuel furnace, not two different furnaces.

2006 INTERNATIONAL FUEL GAS CODE® CHIMNEYS AND VENTS -

"503.5.7.4 Combination gas- and oil fuel-burning appliances. A listed combination gas- and oil fuel-burning appliance shall be permitted to be connected to a single chimney flue. The chimney flue shall be sized to properly vent the appliance."

OT - OF!!!

M.

[hausdok]

I found this in my Code Check HVAC:

Under gas appliance venting - No solid fuel and gas in same vent (IRC 2426.5.7.1/UMC 802.4)

Under oil-burning appliance vents - OK to vent gas & oil to same chimney [iRC 2426.5.6.2/UMC 809.0)

OT - OF!!!

M.

[Steven Hockstein]

What about all of that wacky plumbing? Looks like the plumber emptied out his leftover bin and installed all of the odds and ends in this basement.

[msteger]

Thanks Guys. That cleared things up. I am still puzzled, however, about the code statement about "Combination gas- and oil fuel-burning appliances". Don't think I've ever seen an appliance that burns fuel oil and natural gas. Do these exist?

"2006 INTERNATIONAL FUEL GAS CODE® CHIMNEYS AND VENTS -

503.5.7.4 Combination gas- and oil fuel-burning appliances. A listed combination gas- and oil fuel-burning appliance shall be permitted to be connected to a single chimney flue. The chimney flue shall be sized to properly vent the appliance."

Is the reason the smaller vent has to be on top have to do with less heat and the bottom larger vent will help both vent upward and out?

[hausdok]

Hi,

There are all kinds of multi-fuel furnaces out there. Here's a sample of a few brands:

http://www.yukon-eagle.com/ (Wood/gas)

http://www.woodboilers.com/multi-fuel-furnace.asp (Wood/Oil/Gas)

http://www.charmaster.com/about.html (All types)

http://www.gsa-world.com/index.cfm?id=2 ... r%20burner (waste oil)

http://www2.northerntool.com/product-1/200325990.htm (Corn & Pellets)

http://www.harmanstoves.com/features.asp?id=30 (wood, coal & Oil)

http://www.alternateheatingsystems.com/ ... oilers.htm (coal, wood, & Oil in any combination)

http://www.firefix.com/Harmon_Multi-Fuel_Furnace.htm (Oil, coal, or wood)

OT - OF!!!

M.

[Jim Morrison]

Originally posted by inspecthistoric

Originally posted by msteger

So, if one appliance is fuel oil and one is natural gas, they can share the flue but the gas one needs to be on top of the oil one. Side by side for this example arrangement is NOT OK, correct?

It's not the fuel, It's the size - smallest is always on top.

Originally posted by Jim Morrison

The smokepipe from the water heater should enter the flue above, as it does in your photo.

I've spent a good bit of time in and around Boston. Enough to pick up things like "wicked-good lobsta" and "bang-a-youie", but WTF is with "smokepipe".

Hey Bill,

I've spent too much time in South Central PA to take offense to that. Talk about yer language butchers!

[Hearthman]

NFPA 211 allows interconnection of oil and gas appliances as long as there is sufficient draft for both and both have primary safety controls.

Solid fuel must have its own separate flue unless as a listed combination fuel appliance.

The smaller vent connector goes above the larger simply to allow a little more vent rise off the smaller appliance. If the vent connectors are manifolded into a liner, it isn't a problem.

An unlined flue must always be relined to meet the class of service.

HTH,

Hearthman

[John Dirks Jr]

How long is the horizontal run of the vent pipe for the furnace? Is it mounted horizontal or does it have slope? Could there be a problem with the length and whether or not it is properly sloped?

[msteger]

John:

The run from the furnace to the chimney was approx. 12 feet. There was indeed a pitch upwards towards the chimney connection.

Matt

[John Dirks Jr]

Originally posted by msteger

John:

The run from the furnace to the chimney was approx. 12 feet. There was indeed a pitch upwards towards the chimney connection.

Matt

Couldnt 12 feet be questionable in some circumstances? What was the diameter of the vent? Anyone care to share some rules on vent connector lengths?

[hausdok]

Hi,

Sure, the rule for an uninsulated connector is < 75% of the vertical vent and the rule for an insulated connector is < 100% the vertical vent, with a minimum of 1/4in./ft. toward the appliance.

Buy yourself a CodeCheckComplete - it's worth it.

OT - OF!!!

M.

[John Dirks Jr]

How about with respect to the diameter of the vent? I had read that a rule of thumb is no more than 1 1/2 feet in lenght for each inch of diameter. Therefore a vent 12 feet long should be at least 8 inches in diameter. Would you consider this a good rule to follow as well?

[John Dirks Jr]

I see something else in the picture that makes me wonder. Is that a flexible gas line (yellow coating) at the top of the picture? Where does it go?

It should not pass through a wall or a floor. I hope it's not going through the floor to feed an appliance upstairs. If so...no no no.

[hausdok]

Hi,

I've never read that. It's 7X diameter of the collar max. If you ask me, you're over-thinking it.

OT - OF!!!

M.

[Bill Kibbel]

Originally posted by AHI

How about with respect to the diameter of the vent? I had read that a rule of thumb is no more than 1 1/2 feet in lenght for each inch of diameter. Therefore a vent 12 feet long should be at least 8 inches in diameter. Would you consider this a good rule to follow as well?

I've never seen that written anywhere, but I do get frequent e-mails that tell me I should be concerned with my length and diameter.

I suggest getting out of the habit of calling that pipe a vent. It's best to use the word connector as in "flue connector" or "vent connector".

[Bill Kibbel]

Originally posted by AHI

I see something else in the picture that makes me wonder. Is that a flexible gas line (yellow coating) at the top of the picture? Where does it go?

It should not pass through a wall or a floor. I hope it's not going through the floor to feed an appliance upstairs. If so...no no no.

Where did you read that now? Could you be confusing flexible appliance connectors with CSST?

[hausdok]

Originally posted by AHI

I see something else in the picture that makes me wonder. Is that a flexible gas line (yellow coating) at the top of the picture? Where does it go?

It should not pass through a wall or a floor. I hope it's not going through the floor to feed an appliance upstairs. If so...no no no.

No. That's CSST (corrugated stainless steel tubing). You're thinking about flexible connectors. They follow that rule.

CSST can pass through walls and floors but uses rigid connectors - sort of like PEX.

OT - OF!!!

M.