Harman P43 install - Will 2" outside air kit restrict flow at all or do I need to go with 3"

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Dec 27, 2010
Hudson Valley, NY
I'm replacing my old Englander EP25 with a 4 year old Harman P43 I picked up, yay!

My current outside air kit is 2" and as everyone here knows the Harman uses 2 3/8 flex tube. I have a 2 1/2" to 2" car exhaust adapter that fits nice and snug in the P43 air intake so if I use that, I can use the 2" flex pipe and it would be a clean and tight install.

I have to buy a new outside air kit anyway since the old one is damaged and was wondering if a 3" kit would be better than a 2" I'm not sure if the airflow would be much different between the 2" and the 3" but I think I would prefer the 2" unless the airflow from the 3" would be better.



Minister of Fire
Nov 5, 2011
Kananaskis,Alberta, Canada
I put a 3” on my P61A, any larger airflow is better...think of it as using a tiny straw vs using a larger straw in a drink


Minister of Fire
Oct 31, 2014
South Central NH
The thimble of my P43 only has a hole for the 2" OAK, so that is what I use (connected to a 3" before it goes into the stove) . The stove runs fine. That being said, it is a very short run so YMMV.

My P61a has a 3" on it, which it definitely needs. Used to have a 2" and the 3" is a definite improvement. However, it has a much longer run (about 6') and the OAK is seperate from the thimble so I just had to cut a bigger hole in the plywood.
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