Minimum slope for water heater exhaust flue?

  1. gas-fired water heater 1/4" per foot. Right?
  2. Oil-fired WH?
  3. Gas-fired furnace?
  4. Oil-fired funace?

Kenton is this another version of 20 questions???

James, do you always answer a question with a question? :mrgreen:

Seriously, no, these are very simple questions. I went through the IRC, couldn’t find the answers on the first pass. I suspect they’re there, but I’m runnin’ outa’ time. I’ve got a deadline and would appreciate any help. Don’t know why I don’t know this already but at this point I just need to be accurate. There’s always more to learn… sit down to write a library of narratives and that will become obvious really fast.

wish I could help you Kenton…I’ll back away now and give the experts a chance…jim

Kenton, all the installation instructions, for any of the above, that I’ve ever seen were a minimum of 1/4" per foot but I don’t have a code reference handy.

James and Larry, thanks for answering, I was embarrased to admit I don’t know, can’t find it in the IRC, now I feel a little better but would like to get at the real answer.
Does it vary by jurisdiction? Is it established by the IRC but a little hard to find?

Anyone got an answer for this?


Manufacturers installation instructions for all listed appliances.

I can’t imagine it would vary by jurisdiction and the manufacturer’s installation instructions would prevail.

Heck, just the other day I had a Burnham power vented boiler that required the vent pipe to fall 1/4" per foot toward the termination.

Sorry I can’t help more.

Too drain condensation----:smiley:

Ahhh…What is a Boiler by the way Larry?..:smiley:

Yes, but most often we see them drain back to the furnace to a condensate pump. :wink:

Ah, you should feel fortunate you don’t need to know. :stuck_out_tongue:

just a big or small hot water tank used to heat a house or building Dale…it’s not warm all the time everywhere…some of us need heat from time to time…:stuck_out_tongue:

If you call me soon the answer can be had for $99.00.

Page 312 IRC M1803.3

Ah, but IRC M1801.1 states those requirements only apply to fuel burning equipment other than gas, which needs to be vented in accordance with IRC Chapter 24. The plot thickens … :wink:

For Category-I gas equipment (basically natural draft, standard efficiency), G2427.10.8 requires the 1/4" per foot slope upwards towards the chimney.

For other types of gas equipment, the IRC requires the installation to meet the equipment manufacturer’s requirements.

[P.S. The IRC requirements above apply to water heaters, furnaces, and boilers]


Good question, but a little open ended.
The problem with “your” question is that there are variables that we probably all see in the field, that weren’t mentioned in “your” question.
1- Is the vent H & V run in a totally open area or is part of the venting material passing through combustible materials or encapsulated in chases of combustible material.
2- What type of material are we talking about (ex.- Metal Ridgid Double-Wall/ B’vent type pipe & fittings, Metal Ridgid Single-wall/pipe & fittings, Metal Flexible rated pipe & fittings, PVC Pipe & fittings, etc.).
3- Local codes in our area typically exceed minimum standards set be the Manuf. of the venting materials and/or the Equipment/Appliance Manuf’s. recommendations.
If I see what I think is a problem I always check local code dept’s. when I go outside my local jurisdiction, just in case.