Jump to content

Gas water heater/oil fired furnace sharing flue


Bill Kibbel
 Share

Recommended Posts

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:

200811311312_DSCF0010.jpg

117.38 KB

Link to comment
Share on other sites

  • Replies 52
  • Created
  • Last Reply

Top Posters In This Topic

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.

Link to comment
Share on other sites

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".
Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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?

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

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!

Link to comment
Share on other sites

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

Link to comment
Share on other sites

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".

Link to comment
Share on other sites

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?

Link to comment
Share on other sites

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.

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share


×
×
  • Create New...