Installing Harman P42i-TC myself, have a few questions

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New Member
Oct 27, 2023
Fairfax, VA
I have a Harman P42i-TC 20 inch on order and am planning on installing it myself. I have a 17 foot high chimney with a 1970's era Majestic brand metal fireplace in my house. The chimney is 8 inches inner diameter and has a stainless liner with a galvanized outer shell, it is squeaky clean and in great condition. Plan is to run a 4 inch flex pipe up the chimney. I took the heat shields off the sides to inspect it and ran a borescope into the Majestic vent to see what was going on behind the insert and everything looked great. It's on an outside wall and I can see the outside plywood paneling on the other side of the metal enclosure on the video.

I want to put an outside air kit on the Harman. Looking at the install manual on Page 11. One of the suggested venting methods is to take a 3 inch flex pipe and run it up into the bottom of the chimney then wad it with rockwool or something of that nature to seal it. In this method they don't talk about using a blocking plate or anything, just relying on the rockwool at the bottom to seal everything.

The other option is to use a through the wall outside air kit. I could very easily drill a 3 inch hole in the existing Majectic liner and then through the outside wall of my house to put a vent in. Downside of this method is that it would destroy the Majestic insert and make it impossible to switch back, not that I would ever want to.

Any opinion either way?

If I go out the top should I make and install a blocking plate on the plasma cutter I have at work or should I just rely on the wading with rockwool?

I did some searching around this forum the last few days and have found a few mentions of people talking about how cold outside air could cause condensation in the exhaust pipe promoting creosote buildup. Intaking down the chimney next to the exhaust pipe would preheat the air and reduce this problem potentially, any thoughts on this?

Another random question, is the wireless room sensor worth it?

Sorry if I missed a thread already answering these questions, I tried searching before posting but came up empty.

Anything else? Other install pointers? Pellet recommendations? Hardwood vs softwood?

Thanks for the help, Alex.
I’ve got the intake setup as you mention with rockwool at the bottom , I also made a metal block off plate that wingnuts onto the damper if I ever need to pull it out I can .. no issues for the past 4 years like this, it made a difference in drafts in my home as well, I no longer have the further rooms chilly. I also have the harman cap that allows air down the flue but keeps moisture out.

I was going to install the side by side piping to a different cap but never got around to it and I haven’t had any issues either.

Pellets: wood and sons softwood, turman for hardwood … although harman will burn anything :)
before you do any install you should contact your local inspector as you may have to have a inspection done for your insurance.. Ask then if their you should do or be aware of. I did this when i installed mine and the inspection went quick and inspector was quite happy that i took the extra time to contact him.
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Thanks for the replies. I actually called a local installer and asked them and they said that if he saw that I drilled a hole in the existing metal wood insert he would fail a chimney inspection. He went on to say that the hole in the side could allow fire to exit the enclosure in the event of some sort of stove fire and it is a safety issue. So it seems like I will be going up out the existing chimney with the insulation wading at the bottom.

I did pull a permit, my county requires it. I called the building department and they said they don't have a building code pertaining to inserts they just use the install manual from the manufacturer. So I guess I will just make sure everything is compliant with the install manual.
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