Project: I need to add insulation to my attic. I live a few miles outside Rochester, NY. Most of the attic has only 4 inches of cellulose insulation, and some parts have less than one!

Obstacle: The metal flue and hot water pipes for our baseboard heat go through the attic in an area that has essentially no insulation at all. In the attic I can see bare ceiling drywall over most of the laundry room/utility closet. Before I insulate this area, I have two issues that need addressing:

  • I need something to keep the insulation away from the metal flue - and simultaneously prevent cellulose from falling into the utility closet.
  • I need a way to completely air seal the utility closet from the attic space.

My question: Can I build a plywood box around the flue, all the way up to the roof deck, and then seal the edges with foam? The box would be slightly wider than the hole in the drywall. Would this be a safe and acceptable solution for my two issues?

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  • Are you also looking for suggestions on how to deal with protecting the heating pipes from the sub-freezing temps in the uninsulated attic?
    – Upnorth
    Commented Sep 28, 2017 at 5:04

2 Answers 2


From the photos, the stack is class B venting. You local big box store should be able to supply you with a part called "attic insulation shield". It's just another pipe 2" larger in diameter than your stack & the top gets sealed with a storm collar to fit. Seal with hi-temp silicone and insulation to your hearts content. Stacks that service a zero clearance appliances are not zero clearance as well - only the appliance is.


That looks like a zero clearance exhaust stack, but do verify the manufacturer's label on it.

So, if you want, you can place insulation or plywood right up to it and leave it touching.

I would think you want to wrap insulation around the water pipes to conserve energy and improve heating efficiency. Most hardware and material supply stores sell foam tube sections which can be easily installed around the pipe.

However, the foreignness of this installation makes me want to ask around locally and see if there is any non-obvious reason why it is the way it is. Is it providing heat to the attic and roof that way for a reason? Is there something about that ugly hole in the ceiling providing needed airflow? Etc. I'd start by asking your neighbors who have similar equipment if you can have at peek at their installation.

If they all have a similarly inefficient arrangement, there might be a reason: inquire with a local HVAC for details. If some have a more sensible installation, by all means copy it.

  • Thanks for the reply. We have found other poorly executed DIY stuff in the house. The records I've found indicated it was a foreclosure that someone tried to flip about 10 years ago. We've only been here 2 years. My assumption was that this is yet another thing that was done poorly. I gingerly put my hand on the exhaust stack this morning, while the boiler was running. It felt hot, but not painful. I will get an HVAC contractor out here to confirm. Thanks! Commented Apr 20, 2017 at 20:55
  • The Class B vent shown in the photos is probably NOT "zero clearance", but rather 1-inch clearance, according to the AmeriVent website. The entire stack needs to have the necessary clearance, and your idea of boxing it in should work, provided the stack cannot be moved within the box and the box is at least an inch from the pipe. The shield only needs to go as high as the insulation.
    – Upnorth
    Commented Sep 28, 2017 at 5:00

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