Heater core insulation

[Rudy913]

I have always used pipe \ duct sealant. It looks like a block of black chewing gum. Electricians and plumbers use it to seal up pipes when they drill thru walls. It won't shrink, or rot. Sealing up the airbox will help the fan blow thru the vents better was well

Gardner Bender 1 lb. Plug Duct Seal Compound DS-110 - The Home Depot

Gardner Bender Duct Seal Compound Plug helps seal conduit openings, holes against drafts, dust, moisture and noise. Easy to handle.

www.homedepot.com

Use your method really works greats and easy to apply thank you 😁

 

[565bbchevy]

I just used a piece of foam and cut it to fit, Duct Seal will seal it very well but also over time will collect dirt since it doesn't harden and has a slight tackiness to it also it depends on the look you are going for

 

[57 Handyman]

When I purchased a heater core replacement from Amazon, it came with a closed foam replacement for this opening. However, the Spectre brand heater core part was about 1/2" short in height and required a space being placed underneath.