Thread: Vent Connectors, male up or male down

I call out vent connector installations where the male end of the connectors are facing down because of the potential for flue gas spillage as you can see in the second picture. Wood stove installers seem to be more concerned with condensation and creosote drippings not exiting the stove pipe than with flue gas spillage so they frequently install vent connectors with the male ends facing down.

I'm of the opinion that potential flue gas spillage should be prioritized and the male ends should face up inline with the flow of combustion gases. Which way is correct in your opinion, and what documentation do you use to substantiate your opinion if called on it ?

The pictures are from two different inspections.

Thanks.

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Some googling and it seems I'm in the minority opinion and my opinion is in contradiction to at least a couple of the manufactures installation instructions, for single walled stove pipe, that I was able to dig up. Here's a quote from one of them.

"The reason to have the crimped end of the pipe pointing toward the stove is so that any condensation inside the pipe will flow harmlessly back to the stove, rather than leak out the joint and on to your hearth."

Is anyone of the same opinion as I am and thinks the manufacturers are prioritizing the wrong issue ?

The IRC refers you to NFPA 211, which requires the male down for solid fuels. Gas and oil can be either way. If you are getting spillage of flue gases on a natural draft appliance, you have Combustion Appliance Zone depressurization With Respect To flue gas pressure. Otherwise, natural draft creates a venturi effect that will inhale room air through gaps in the pipe, draft hoods and barometric dampers.

Now, if you clog the chimney, you can get blow-by through such joints. Either way it is a red flag for a qualified professional to determine why it is spilling but the male end orientation is a myth regarding flue gases blowing out of the joints under normal conditions. Be advised some mfrs. of 80% furnaces do not recommend channeling flue gas condensate back into the heat exchanger.

Thank you Bob...sounds like I've been over stepping if not wrong and need to change my opinion and comments. It's difficult for me to agree with the male end down recommendation though. In practice with less than ideal firing (especially with solid fuels) questionable make up air and postponed cleaning of flues...vent connector spillage is far too common. Seems to me the orientation of the male ends facing up in line with the flow of gases would reduce spillage when the draft is less than ideal.

Why the difference between solid fuel and gas or oil and what do you recommend for gas and oil....male end up or down ?

Thanks.

Originally Posted by Robert Foster

Thank you Bob...sounds like I've been over stepping if not wrong and need to change my opinion and comments. It's difficult for me to agree with the male end down recommendation though.

It is my intention that I never put any opinion in a report that I do not have written documentation that backs up that opinion. I am of the firm opinion that what I think does not really matter...I was hired to convey facts...not opinions based on....well...other opinions.

Originally Posted by James Duffin

It is my intention that I never put any opinion in a report that I do not have written documentation that backs up that opinion. I am of the firm opinion that what I think does not really matter...I was hired to convey facts...not opinions based on....well...other opinions.

I don't see a smilie face to suggest you are joking so...

...while that's an interesting idea, several areas where that idea might be difficult to apply come to mind.

What criteria and supporting documentation do you use for calling out that the paint on the exterior trim has reached the end of it's useful service and that the trim should be prepped and paint reapplied ?

How about loose stair railings or guards....how much deflection do you allow before calling it a concern?

How about the functional flow of the water supply ?

Originally Posted by Robert Foster

Thank you Bob...sounds like I've been over stepping if not wrong and need to change my opinion and comments. It's difficult for me to agree with the male end down recommendation though. In practice with less than ideal firing (especially with solid fuels) questionable make up air and postponed cleaning of flues...vent connector spillage is far too common. Seems to me the orientation of the male ends facing up in line with the flow of gases would reduce spillage when the draft is less than ideal.

Why the difference between solid fuel and gas or oil and what do you recommend for gas and oil....male end up or down ?

Thanks.

With solid fuel, male up allows combustible creosote to seep out of the pipe down over the stove where it can ignite. At the very least, it makes a sticky mess. Wood has been male down for over 30 yrs.

If you have questionable MUA and lack of maint. then those problems need attention--not the orientation of the pipe. Properly installed and operated, make down does not spill smoke.

Again, your male up theory is flawed according to physics and experience. Any gaps in the pipe around male ends will draw room air into the pipe due to the Bernoulli Effect (venturi). If you don't have negative vent pressure then you have larger problems than the stovepipe.

Smoke is stupid and does not read directional arrows or look for male crimped ends. Smoke flows from higher pressure to lower pressure and hotter to cooler--that's it. If the smoke is going the wrong way, then figure out which of these parameters is off and correct that parameter such as balancing air pressures or burn hotter fires. If you have flow restrictions, sweep the chimney and assess the layout for best performance.

Bob Harper is 100 % right about the negitave pressure in the venting system and in the home. The new NFPA 31, 2011 Edition, Standard for the Installation of Oil Burning Equipment addresses the direction of the connector pipe in oil-fired appliances.

6.6.28 states: Single wall connector pipes shall be install by one of the following methods:
(A) In accordance with the appliance manufacturers instructions.
(B) With the crimpted end toward the chimney.

As Bob H said, IRC referes you to NFPA211. NFPA 211 referes you to NFPA 31

Originally Posted by Robert Foster

Thank you Bob...sounds like I've been over stepping if not wrong and need to change my opinion and comments. It's difficult for me to agree with the male end down recommendation though. In practice with less than ideal firing (especially with solid fuels) questionable make up air and postponed cleaning of flues...vent connector spillage is far too common. Seems to me the orientation of the male ends facing up in line with the flow of gases would reduce spillage when the draft is less than ideal.

Why the difference between solid fuel and gas or oil and what do you recommend for gas and oil....male end up or down ?

Thanks.

I also agree with Bob's logic. To directly answer your question, the logic for the gas or oil-fired appliances having the crimped (male) end of the connector facing away from the appliance has to do with the potential force created when the burner fires, creating a temporary situation where it (the exhaust gas) is under positive pressure. At that point having the male end "up" allows that force to dissapate within the connector. The entire venting system is ordinarily under negative pressure, otherwise known as draft.
That scenario is unlikely with a wood burning appliance unless you have too much force created by runaway combustion, like especially dry wood, and a restriction in the venting system. That restriction could be a blockage or a flue that is marginal in size.

Ashley Eldridge
CSIA Director of Education
Chimney Safety Institute of America

Bob, John & Ashley....thank you for the education...I downloaded an older copy of the NFPA 211 document last night and started studying.

From what I remember from my college days, whether the male was up or the male was down didn't make a difference. It didn't seem to be a priority at the time.

Originally Posted by Eric Barker

From what I remember from my college days, whether the male was up or the male was down didn't make a difference. It didn't seem to be a priority at the time.

I wondered when I typed the title how long it would take before this thread took this turn.

Originally Posted by Ashley Eldridge

I also agree with Bob's logic. To directly answer your question, the logic for the gas or oil-fired appliances having the crimped (male) end of the connector facing away from the appliance has to do with the potential force created when the burner fires, creating a temporary situation where it (the exhaust gas) is under positive pressure. At that point having the male end "up" allows that force to dissapate within the connector. The entire venting system is ordinarily under negative pressure, otherwise known as draft.
That scenario is unlikely with a wood burning appliance unless you have too much force created by runaway combustion, like especially dry wood, and a restriction in the venting system. That restriction could be a blockage or a flue that is marginal in size.

Ashley Eldridge
CSIA Director of Education
Chimney Safety Institute of America

Ashley,

Interesting point of view on the positive pressure. But in real life how long does this "positive" pressure last, being the other end of the pipe is open (assuming the chimney and "stove piping" has been sized according to the manufacturers instructions)?

Some metal chminey manufactors, in an oil fired situtation, indicate that want the male end down (toward the furnace, water heater) to allow condensation to drain into the appliance and not out of the stove pipe. In this situtation can the metal chimney assembly be considered an appliance also?

Rich

Originally Posted by Rich Goeken

Ashley,

Interesting point of view on the positive pressure. But in real life how long does this "positive" pressure last, being the other end of the pipe is open (assuming the chimney and "stove piping" has been sized according to the manufacturers instructions)?

Some metal chminey manufactors, in an oil fired situtation, indicate that want the male end down (toward the furnace, water heater) to allow condensation to drain into the appliance and not out of the stove pipe. In this situtation can the metal chimney assembly be considered an appliance also?

Rich

Rich, it does not last long. The chimney manufacturer does not overrule the appliance manufacturer when it comes to the appropriate direction of the connector. I believe if it is not specified by the appliance manufacturer one must consider which is more important, the condensation or the ability for small amounts of the exhaust to escape the connector. If the manufacturer does specify the direction of the breeching, then by all means follow their advice. They have made the determination for you and it is clear.

If the male end is designed to be attached to the appliance it should naturally allow the chimney to enter the female end of the connector. That will create a drip-free arrangement at that point. Even in cases where the connector has the male end directed away from the appliance, an adapter can be used to create this "drip-free" connection. It is usually easy to determine the manufacturers' preference by which end of the connector fits properly on the exhaust outlet.

A chimney is a chimney and the appliance is an appliance. They are not the same. Combustion takes place in the appliance and the chimney contains the products of combustion and is not expected the support combustion.

Ashley Eldridge
Director of Education
Chimney Safety Institute of America

Originally Posted by Robert Foster

Some googling and it seems I'm in the minority opinion and my opinion is in contradiction to at least a couple of the manufactures installation instructions, for single walled stove pipe, that I was able to dig up. Here's a quote from one of them.

"The reason to have the crimped end of the pipe pointing toward the stove is so that any condensation inside the pipe will flow harmlessly back to the stove, rather than leak out the joint and on to your hearth."

Is anyone of the same opinion as I am and thinks the manufacturers are prioritizing the wrong issue ?

Well I have been using wood stoves for about 30 years and place the crimped end towards the stove. Cuts down on the unsightly black stain of creosote on the hearth running onto the floor when burning NOT SO SEASONED wood..
DL