Thread: Vent connector length at WH draft hood

What is the minimum length (height) of the straight vent connector at the draft hood before it can be connected to a 90 degree elbow? I think it's 12" but want to make sure. I recall seeing a post had some very nice illustrations depicting dimensions and clearances but cannot find it now.

Same rules apply to a gas-fired furnace?

Thanks.

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Originally Posted by Stanley Chow

What is the minimum length (height) of the straight vent connector at the draft hood before it can be connected to a 90 degree elbow? I think it's 12" but want to make sure. I recall seeing a post had some very nice illustrations depicting dimensions and clearances but cannot find it now.

Same rules apply to a gas-fired furnace?

12" is correct.

All the charts start with a 12" connector length and then get longer from there.

Yes, that applies to all gas appliances with vents and vent connectors.

Thanks for your response Jerry. Any idea where I can find those graphics? I know I saw it in one of the posts here...but can't seem to find it.

12" of vertical rise before an elbow is certainly desirable for good vent design but I do not believe it is a code requirement. Another poster said all the charts start with a 12" lenght but that is only in the multiple appliance tables. The single appliance tables do not even have a column for rise. Additionally, connector rise is measured as the total vertical height change from the appliance outlet to the chimney or vent connection, irregardless of elbows in between. In other words, you could have an elbow directly on the outlet, then a horizontal section, and then a two foot vertical section and it would count as two feet of rise.

Originally Posted by Stanley Chow

Any idea where I can find those graphics?

If you have the IRC, or go to the IRC online, they are in Appendix B.

Then go to Table G2428.3(1) and look at the column for 'Connector Rise', you will see that the least connector rise is 1 foot.

Originally Posted by Jim Brewer

12" of vertical rise before an elbow is certainly desirable for good vent design but I do not believe it is a code requirement. Another poster said all the charts start with a 12" lenght but that is only in the multiple appliance tables. The single appliance tables do not even have a column for rise.

The vent connector rise is not shown in those tables because those tables are for "Appliance Vent Connection" = "Connected directly to vent", thus there is no *separate* "vent connector rise" just "vent" height ("rise"), and that vent rise still needs to be 1 foot before it turns from the vertical (refer to drawings in Appendix B).

Originally Posted by Jerry Peck

The vent connector rise is not shown in those tables because those tables are for "Appliance Vent Connection" = "Connected directly to vent", thus there is no *separate* "vent connector rise" just "vent" height ("rise"), and that vent rise still needs to be 1 foot before it turns from the vertical (refer to drawings in Appendix B).

The tables with zero entries are the single appliance tables and the zero entry appears in the column for lateral, and has nothing to do with rise.

The original question asked what is the minimum height of vent connector before an elbow, and the answer remains zero. Certainly, the more you have the better the installation will perform but there is no stated requirement (in the code) for 12" as others have suggested. You might find it in the manufacturer's installation requirements for the appliance.

Also, you can't prove the requirement through the venting tables because the venting tables are only one of the approved methods for vent sizing. In other words, even if the 12" height requirement was stated in the venting tables it would still not be an absolute requirement because the venting tables aren't mandatory. It is probably true to say a 12" minimum height is required if you are sizing a multiple appliance installation via the tables since the lowest rise in the tables is 1 foot. However, rise isn't a factor in venting tables for single appliances nor is it a factor for other sizing methods which are approved by the code.

So, to the OP, be careful how you word your report. If you say a 12" minimum rise is recommended (for good vent performance) you can probably get away with that but if you state it is required you should be prepared to document your source if questioned.

Originally Posted by Jim Brewer

The tables with zero entries are the single appliance tables and the zero entry appears in the column for lateral, and has nothing to do with rise.

The original question asked what is the minimum height of vent connector before an elbow, and the answer remains zero. Certainly, the more you have the better the installation will perform but there is no stated requirement (in the code) for 12" as others have suggested. You might find it in the manufacturer's installation requirements for the appliance.

Also, you can't prove the requirement through the venting tables because the venting tables are only one of the approved methods for vent sizing. In other words, even if the 12" height requirement was stated in the venting tables it would still not be an absolute requirement because the venting tables aren't mandatory. It is probably true to say a 12" minimum height is required if you are sizing a multiple appliance installation via the tables since the lowest rise in the tables is 1 foot. However, rise isn't a factor in venting tables for single appliances nor is it a factor for other sizing methods which are approved by the code.

So, to the OP, be careful how you word your report. If you say a 12" minimum rise is recommended (for good vent performance) you can probably get away with that but if you state it is required you should be prepared to document your source if questioned.

I am going to presume that you understand enough, and know enough, that a vent can be connected to the appliance either with a vent connector or by directly connecting the vent to the appliance, and that you can use single wall or double wall connectors to connect to the double wall Type B Gas Vent.

Further, I will presume that you understand that when a vent which is directly connected to the appliance, the fist section of vent is also serving as the connector.

Additionally, I will presume that you have read various manufacturer's installation instructions and understand and know that they state there must be a minimum rise of 12 inches above the draft hood for the connector (which is also the first section of a directly connected vent).

Please correct me if my presumptions of what you understand and know are incorrect.

Being as you understand and know the above (at least I am presuming that you do understand and know the above), then you will understand that the minimum rise before the first elbow is 12 inches ... whether or not the vent is a directly connected vent and is connected to only one appliance, or whether or not the vent is a directly connected vent and is connected to one of multiple appliances, that the manufacturers, and the code which incorporates the manufacturer's installation instructions by reference, require a 12 inch minimum rise before offsetting.

Therefore the OP has been made aware of the 12" minimum rise requirement.

Jerry, thanks for telling me what I know but that wasn't really necessary as I have a pretty good handle on that already. While most of your points are irrelevant to the discussion allow me to correct one of your points about what you think I know. I don't know that all water heater manufacturers require a 12" rise, because they don't. As I said in an earlier post, some manufacturers may require that. I'll add here today that while some may, most don't. Most manufacturers have no reference to a 12" minimum rise requirement, while State Water Heaters have the following: "It is recommended (but not mandatory) that a minimum 12 inches of vertical vent pipe be installed on the draft hood prior to any elbow in the vent system." (That was a direct copy and paste from a State manual)

So Jerry, code doesn't require it, most manufacturers don't require it, so what makes you think it is a requirement? Actually, I'm not sure that any manufacturer does require it because I've seen a lot of manuals and don't remember it. It is not a requirement that manufacturers would want to include because it is likely to conflict with clearance requirements, and could cause some loss of sales. Imagine a basement with a low ceiling where you couldn't get the 12" rise and maintain adequate clearance to the (combustible) ceiling or floor joists. In that case what do you think the manufacturer would say? Maintain the clearance for fire safety or maintain the rise for some small benefit in performance?

So to sum it up, if a HI states on his report that a 12" vertical rise before elbow is required he should be prepared to document his source.

Originally Posted by Jim Brewer

Jerry, thanks for telling me what I know but that wasn't really necessary as I have a pretty good handle on that already. While most of your points are irrelevant to the discussion allow me to correct one of your points about what you think I know.

Jim,

Let me correct you in correcting me - I didn't tell you what you knew, I said what *I* *presumed* that you knew. I also left it open for you to correct me on those presumptions where I was presuming that you knew.

I don't know that all water heater manufacturers require a 12" rise, because they don't.

Again, "vent" .... the "vent" is what is being discussed, not the "water heater", thus it is the "vent" manufacturer's installation instructions which need to be referred to, not necessarily those of the water heater manufacturer.

So Jerry, code doesn't require it, most manufacturers don't require it,

Most "vent" manufacturer's require it, that is why it is a code requirement.

Jim, you need to keep track of what is being discussed, in this discussion that is the "vent", not the "water heater".

in this discussion that is the "vent", not the "water heater".

Jerry,
The OP started with this:

Vent connector length at WH draft hood

So I believe there is some relevance to discussing the product's use or application.

Jim,

The first thing to keep in mind is that there is a 'vent connector' installed in the vent system which 'connects the vent to the appliance', this is whether the vent is directly or indirectly connected to the appliance.

An indirectly connected vent means that a listed 'vent connector' was used to connect the vent to the appliance.

A directly connected vent means that the vent is connected directly to the appliance and the first section of the vent becomes the vent connector which connects the vent to the appliance.

If the above is not understood, then trying to explain the rest becomes a moot point - so, as in my first response to you, *I am presuming that you understand and know that*, and, again, please feel free to correct me if I am wrong in what I am presuming that you know.

With the above out of the way ...

Here is one vent installation instructions for you: (bold is mine) http://www.duravent.com/docs/product/L204_Mar2011.pdf
- Scroll down to page 5, left column, last line, continues to top of right column below Figure 2, "8. Connector Rise. Plan a minimum of one foot vertical connector rise coming out of each appliance."
- Remember, the "vent connector" can be a special listed piece or the first piece of the vent which connects to the appliance.

Here is another vent installation instructions for you: (bold is mine) http://www.hartandcooley.com/Librari...?download=true
- Scroll down to page 5, left column, at the bottom, and continues at the top of the right column, "Connector Rise The immediate vertical height from the flue collar to the first turn (connector rise) will have an important effect on the proper functioning of a venting system. In order for a venting system to prime (for flow up the vent to start), the vent MUST be heated by the flue gases. If it is easier (less resistance) for the flue products to spill out the draft hood relief opening than to flow into the vent, priming can be delayed or prevented altogether. By using all of the vertical height (head room) available (NEVER less than 1 foot), a venting system will usually prime within 8 to 10 seconds. Small increases in connector rise generally have a greater impact on vent capacity than an increase in common vent height."

Now, referring back to the code and the drawings in Appendix B, you will see that even the single appliance connected vent has a vertical vent connector rise. The above description of a directly connected vent explains this.

Originally Posted by Dom D'Agostino

Jerry,
The OP started with this:

"Vent connector length at WH draft hood "

So I believe there is some relevance to discussing the product's use or application.

And we are discussing that, but one refers to the *vent installation instruction instructions* for the installation of the vent, and the OP was not questioning the installation of the water heater, he was specifically questioning the installation of the vent.

The OP also said: "Same rules apply to a gas-fired furnace?"

And my reply was "Yes, that applies to all gas appliances with vents and vent connectors."

And "vents" and "vent connectors" has been the discussion since then. The OP is not asking if the water heater needs to be raised 18" above the garage floor, he is asking about the vent and its connection.

Jerry,
You found some vent manufacturers that require the 12" rise. Great. There are plenty more that don't so it is not a universal requirement. How about a water heater vented with single-wall galvanized pipe connected to a masonry chimney? Neither the single-wall connector nor the masonry chimney have installation instructions so there is no requirement there.

So again, if the HI states a 12" rise is required (before an elbow) he should be prepared to document his source.

Originally Posted by Jim Brewer

Jerry,
You found some vent manufacturers that require the 12" rise. Great. There are plenty more that don't so it is not a universal requirement. How about a water heater vented with single-wall galvanized pipe connected to a masonry chimney? Neither the single-wall connector nor the masonry chimney have installation instructions so there is no requirement there.

So again, if the HI states a 12" rise is required (before an elbow) he should be prepared to document his source.

That's when you go to the code and follow it to Annex B and look at the drawings showing how it is to be installed, and go 'Golly gee, that thar drawing shows thar are a rise between da draft hood and da elbow.'

Sorry about that back woods country reference wording, but that is what you are stretching trying to reach, so I figured I would provide that for you.

As long as the OP understands what is what, I can see that you are beyond reasoning with. I suspect that you are the kind of person who wants the code to be specific on every nail and screw and then would complain that the code was overly restrictive, bulky, and unwieldy to use if it was that way.

Are you aware that the water heater manufacturers (all that I have seen) REQUIRE the draft hood to be anchored to the top of the tank? Yep, the draft hood is part of the water heater and is therefore in the water heater instructions. How many draft hoods do you find anchored to the top of the water heater? I'm going to guess 'none', if you even looked for that.

Jerry,
Now you are just being nasty and childish. I'm done.

Originally Posted by Jim Brewer

Jerry,
Now you are just being nasty and childish. I'm done.

No, I'm not, I'm responding to the way you are stretching for support of your answer.

We have another one or two here who state things and then do not provide support, it's supposed to be their way because they say it is their way.

Hey Jerry and Jim....

I'm the OP'er. I thought my question was a simple verification of my basic understanding of gas-fired appliance vents and their recommendations/requirements. What I got out of this post was more than I bargained for....so thank you both for sharing your knowledge and expertise. Opposing viewpoints are good and healthy so we can learn both sides of the coin on how different folks view the same issue. It's a great education for us less knowledgeable folks...like me. Where it becomes bad, less healthy and unprofessional is when the dialogue starts to go downhill. Guys...it's going downhill. This forum is for professional folks to share and learn from each other. To do that...we all have to maintain our sense of professionalism towards each other.

So I propose that we end this thread and enjoy a nice glass of wine.

I have great respect for you guys. Thank you very much for all the great knowledge that you've shared with us.

Stan

Jerry,
Thanks for providing the manf's requirements for a distance that I have always been told to use. It is easy to say "do it this way", but the person who can document the rules is the one to listen to.