LP Gas Fireplace Direct Vent Technical Question:

LP Gas Fireplace Direct Vent: Once the vent exits the exterior wall of the home, is ANY horizontal run allowed? If so, what are the limitations? (Manufacturer of fireplace and vent unknown).

Please supply the source of your information. If only an opinion, please state that it is so.


See attached photo’s…

Clearance graphic… does not address horizontal runs…

One manufacturer of direct-vent fireplaces, Lennox, allows a maximum of 20’ horizontal run only if 4.5’ of vertical run is provided above the firebox.

Very interesting. Thanks Mike. Much appreciated.

I have never seen a horizontal run before, after exiting the exterior wall.

I visited a fireplace store this morning and discussed the scenario with a service tech, and he stated that horizontal runs are not allowed at all.

I have a call in to a “Sweep”, but haven’t received his return call yet.

No AHJ on duty today (Saturday).

Please continue to reply with any additional info. This is one of those rare occassions where we can all learn from something not often seen. :slight_smile:

It would have been wrong to terminate where it left building. For direct vent appliances always check the unit manufacturer installation requirements. A lot of gas codes have not caught up to them yet. Looks like a good install to me.

If there was a power vent installed, it’s limitations would be similar to this here;


As for a non power vent or direct vent, using a Regency I have installed in my own house, it is limited to a 10 foot horizontal run + an 8 foot rise at the end of the vent.


The first chart I posted was for what Lennox refers to as a “vertical vent”. Here is another graphic for their “horizontal vent” and indicates as much as 10’ vertical is needed. This diagram is closer to your real world example.

Lennox DV2.JPG

Here’s a link to a Lennox Installation Manual and you can better understand their requirements (which vary by model and might very well be different than other manufacturers of course).


See pages 17-20 for horizontal vent installations.

Thanks guys. I appreciate everyones assistance with this.

I presented all of the information to my client, and since he will be having a service tech out for service due to an ignition concern, I recommended that he have the entire flue system evaluated for function and compliance to manufacturers requirements.

Please continue adding any comments for future reference.

it looks like one of those new fangled deck warmers to me…

Any signs of condensate leakage or corrosion from leakage should be noted.

Based upon your climate zone, condensation of combustion gases producing water and nitric acid will accelerate flu deterioration. The longer the run, the greater the potential.

Also potential snowfall levels and flue termination elevation. Snow can hold a lot of combustion gas byproducts which could reenter the house from the snow piled up against it.
(Comments based upon your geographical location)

That is actually my primary concern, that none of the Manufactures seem to address in their manuals… the horizontal run on the EXTERIOR of the home. They all address INSIDE the home. There is basically 18ft of exposed venting to the elements. (Akin to uninsulated venting through a cold attic, only worse). The system looked new with no indications of any condensation or deterioration… YET. Connections, hangars, slope rise, vent cap termination height and distance to vinyl siding, everything looks professionally installed, but I just can’t get my head wrapped around it. It continues to bug me, and a few more calls on Monday may be in order. I want a definitive answer on this. I don’t like ‘gray area’ reporting!

Did you find your answer as too the validity of this install? Is this safe or does it pose a fire hazard in years to come? I’m new to this, if this question is illegitimate I’m sorry.

Hey Ryan… no problem with your question. Glad to see that you wish to learn.
Unfortunately, I never came up with any more definitive information than what is in this thread. I still think about it from time to time, and it still bugs me. Everyone I talk to about it either admits they just don’t know, or many say “don’t worry about it”. Calls I’ve made yielded zero help. Tech nowadays simply reads out of the manual… totally useless!
If and when I ever get more useful information, I will be sure to followup and post it in this thread. Feel free to add any input or opinions you may have. One never knows where a key piece of info will come from.
Good luck to you.