Garn horizontal flue maximum length

[surefire]

Hi, my name is Chris, and this is my first post. I've been reading here for weeks though, and I have to say this site is an amazing resource, as are all of you who share.
I've been dreaming about having a Garn someday...
What would be the maximum length one could go with a horizontal flue beyond the exterior wall of a building? I realise that at some point friction resistance and Duratech flue wall cooling would be a factor. I'd like to go 16' if possible (to clear a porch and its inside corner).
Thank you!

 

[mike van]

Could you go vertical instead?

 

[heaterman]

You can download the entire manual which covers installation and design at
http://www.garn.com/garn-whs-manuals/

 

[surefire]

Thanks heaterman. On your advice I have read over the section on flue design again, but I still see no mention of maximums, only minimum specs (24").

 

[heaterman]

Have to say that's a question I have never encountered..... Will there be an elbow in the flue anywhere?
I think the max I have seen listed for vertical units was something like 18' but I haven't ever had occasion to find out about the horizontal vent.

I'll get an answer for you and then we'll both know.

 

[cityboy172]

If garn doesn't have anything to say about it, I would refer to a NFPA book after that.

 

[heaterman]

Hi, my name is Chris, and this is my first post. I've been reading here for weeks though, and I have to say this site is an amazing resource, as are all of you who share.
I've been dreaming about having a Garn someday...
What would be the maximum length one could go with a horizontal flue beyond the exterior wall of a building? I realise that at some point friction resistance and Duratech flue wall cooling would be a factor. I'd like to go 16' if possible (to clear a porch and its inside corner).
Thank you!

Just to clarify.......you are talking about 16' of horizontal flue correct? No transition to vertical? Just a straight 16' shot right out of the back of the Garn.
If so, how much of that length is outside the building?

 

[surefire]

Correct, no transition to vertical, just a 16 foot horizontal straight pipe. The usual amount inside, say 1-2'. I'm working on an alternate plan but I'd still be curious about the max recommended length. Thanks.

 

[heaterman]

Well here's the crux of the issue. While the Garn combustion blower is certainly capable of handling it, the manufacturer (in fact all manufacturers) of the Class A pipe will not allow that much horizontal flue length.
The problem is flue gas condensation laying in the horizontal pipe, eventually working its way into the gaps in the joints and saturating the insulation. This of course leads to total loss of insulating value and you are left with what is basically very heavy single wall pipe. Dura-Tech, the manufacturer that Garn uses will allow a maximum of 6' and that is it. All Garn's normally come with 4'.
I looked in every code book I have and could find nothing about it. The reason it's not covered is when it comes to venting, all codes follow manufacturers specifications. Being that no manufacturers of Class A pipe allow such a configuration, the codes don't even mention it. It's just not done.
I ran it past Martin Lunde, the owner of Garn and it stumped him too at first. He said they had never had that question posed in all the years of making the Garn. He referred to the manufacturer and got the word straight from the horses mouth.
So long story short, it's not an option.

 

[Woodfarmer1]

On that note, how should the pipe be run to prevent the condensation from laying in the pipe. Should it have more slope down to run out the end of the pipe? As opposed to sloping up to run back into the boiler?

 

[S.Whiplash]

Bottom line keep your horizontal to less than 6 ft. and you won't have a condensation issue. Better yet go vertical right off the Garn. If your plan doesn't pass with the manufacturers you don't have a hope in h*ll of making it happen with your insurance agent.

 

[surefire]

Thank you very much heaterman. I'm glad you were able to run it by Martin Lunde; I know he'll add this info to future versions of his amazingly-detailed installation and owner manuals. That attention to detail gives a prospective buyer confidence!

As for me, I'll get something figured out that will allow the proper flue length.

Thanks again!

Chris.