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Ruud Deluxe Drum 90 Plus Furnace

5920 Views 5 Replies 2 Participants Last post by  yuri
Please bear with me, I am newbie to this forum. I have a Ruud Deluxe Drum 90 Plus furnace which is aprox 13yrs old. I attached a picture of the furnace itself and then a second picture which is a close of the the area where I have my question. On the close up picture there was previously some type of mastic or putty which created a seal around the PVC to the metal duct. When I replaced the filter today I notice for the first time that the mastic or putty appears to have worn or melted away and is now allowing the warm air to escape into the unconditioned basement.

Most importantly, I first want to make sure this is not serious and allowing carbon dioxide to escape into the household. I have temporairly shut off the heat just in case. Second, what can be done to fix this, is it simply purchasing the mastic (or whatever it is) again and creating a good seal once again. If so, what should I look for when buying it ? Or, is the problem more extensive and a lot of work involved to fix the problem. If more extensive please try and let me know the amount of work involved so I know when calling a professional in to address the problem.

Thanks very much for your help and assistance.


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It is not dangerous and losing a bit of hot air thru there won't hurt anything. It is a mastic which Pros use and is probably unavailable to the public. I would scrape it all away and clean the metal with a bit of WD40 to dissolve the remaining goop or use Goo B Gone cleaner. Then lightly sand the metal and use a good quality white or clear bathroom silicone. Simple as that.:thumbsup:
Thanks Yuri for the quick reply. It's good to know that it's not dangerous and leaking carbon monoxide into the household. I understand what you recommended but the hole to patch I think is a bit too large for just regular silicone caulk. Might you be aware of where to obtain the mastic you referenced. I think will be bulkier and fill the gap much better. Appreciate the help !
I would use silicone just cut the tip of the dispensor tube so it is about 1/4 to 3/8" wide and shoot a large amount in that hole. I have filled holes 2-3X that size and we use it all the time to seal AC lines where they enter the house. Silicone can withstand the heat easily and takes 10 or more yrs to shrink. I use silver foil tape but that takes a bit more skill. That black mastic I don't know where you get it and usually you have to buy a pint or quart or more at a time when you buy the grey mastic (which is commercial stuff and gives off lots of fumes). Probably costs at least $20 a pint and a tube of good silicone is $3-4.
Thanks again Yuri appreciate your advice. Will do what you suggested today.
Yur Welcome.:yes:
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