I'm installing a 45k BTU gas heater in my garage. It will be a vertical vent installation with 3" b vent pipe and I'm going to insulation the attic with about 18" of cellulose insulation.

No one in town has an attic insulation shield in stock so I was thinking of building one. Either Plywood that would be about 6x6" or 7x7" and go from the firewall support to the roof or getting a 6" piece of pipe and put a storm collar on the top. Depending on the final heater placement the distance from the ceiling to roof could be less than 18". Suggestions?


I would search 'wall thimble' or 'flue pipe wall thimble' for what you need. You can order Dura Vent wall thimble on line from Home Depot for about $60.00 or from eBay or Amazon and have it shipped to your home. Why try to make something that is engineered to work correctly and is readily available. Make sure that "B" vent is designed for the type of heater you are installing and for that type of fuel.

  • This is a vertical vent install not horizontal and yes b vent is right for this application. – DelzSQL Dec 7 '18 at 15:47
  • Also, a wall thimble is not the same thing as an AIS. I have the fire stop already in hand. Also as previously mentioned an out of the box AIS might not fit depending on the final heater mount location so I’m just checking out my options. I have googled it and just wanted to see if anyone here had any suggestions or experience with their own. – DelzSQL Dec 7 '18 at 15:54
  • They may not be the same thing but they do the same job (preventing a fire) – d.george Dec 11 '18 at 12:14
  • Right, but they prevent different things from catching fire. I guess I could drain my engine of oil and put in axel grease because they are both lubricants. – DelzSQL Dec 12 '18 at 13:30

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