Does this CGi gas boiler direct vent setup require double wall pipe or not?

Jells · October 10

I've contracted to have the masonry chimney demoed and replaced with the snorkel direct vent, but they claim it doesn't need to be double walled. It seems like a liability to me to have a unprotected fully hot vent at ground level!

This is from the manual, page 15. https://www.weil-mclain.com/wp-content/uploads/CGi-S4-Boiler-Manual-0124.pdf

Obtain vent system components

The following special gas vent systems comply with UL-1738
and ULC-S636 standards and are certified by CSA as the only
systems suitable for use with CGi boilers (all 3” diameter):
• Heat-Fab, Inc. Saf-T Vent®
• Flex-L International, Inc. StaR-34
• Z-Flex®, Inc. Z-Vent II
• ProTech Systems FasNSeal

Can/should/must I require they use double walled pipe?

Previous discussion of options https://forum.heatinghelp.com/discussion/204544/what-to-do-with-this-odd-boiler-vent-setup-redirecting-the-vent-into-the-old-chimney#latest

EBEBRATT-Ed · October 11

Yes. it has to be 1 of the 4 pipes above

• Heat-Fab, Inc. Saf-T Vent® • Flex-L International, Inc. StaR-34 • Z-Flex®, Inc. Z-Vent II • ProTech Systems FasNSeal

Listed for the install. Nothing else can be used.

hot_rod · October 11

I think you have a class 3 requirement if that is a fan assist boiler.

So the common double wall B vent cannot be used. Stick with the list.

Double walled is used when you have reduced clearance requirements

Jells · October 11

https://forum.heatinghelp.com/discussion/comment/1906046#Comment_1906046

So if they can't use double wall, what do I do to make it safe? I don't have small kids but theoretically it's a burn hazard. Do I need to put chain link fence around this thing??

EdTheHeaterMan · October 11

Can you show us a photograph of the location for the expected termination of the vent pipe? Are you sure you need it to be a "Snorkel" configuration?

The Category III vent is for exhaust temperatures that usually range above 140°F, so that is somewhat of a concern when it comes to actually touching the metal vent pipe while the appliance is operating. I might place a metal cage around the vent pipe, with a clearance of about 3 inches from the pipe, using a material that will not allow fingers to get too close to the hot vent pipe. Placing a chain link fence will do the same thing however you would need to be farther away since a small child can fit their arms thru the fence. I have seen expanded metal mesh that will do what you are suggesting.

Screenshot 2026-10-10 at 10.48.43 PM.png

hot_rod · October 11

https://forum.heatinghelp.com/discussion/comment/1906056#Comment_1906056

you can use double wall as long as it is listed for Cat. 3 This is one brand on the Weil list you posted.

Which may be a nicer look than chain link fence.

The double wall add some insulation, I don’t think I would run much distance of single wall outside.

You can download venting manuals, most manufacturers use NFPA code guidelines.

Jells · October 11

https://forum.heatinghelp.com/discussion/comment/1906060#Comment_1906060

Thanks, that's what I needed to know. I'm going to tell the contractor that I want it double walled.

HVACNUT · October 11

EBEBRATT-Ed · October 11

These vent systems are specific to that boiler. All you have to do is follow the Weil McLain instructions regarding material and install

ratio · October 11

Sounds like this is a hazard that the mgr's engineers didn't consider (as if such a thing is possible). IIWM, I'd talk to the AHJ & see what they say. It doesn't sound like something that has never happened, I bet the inspector has come across this & seen the solution already.

Does this CGi gas boiler direct vent setup require double wall pipe or not?

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