Sealing gas duct vents with silicone



Vlad K

Last Updated February 17, 2016 01:09 AM

Is it okay to use silicone to seal gas furnace heater supply ducts? If so, do you know how long the silicone will need to cure before the system is useable?

Some background: I've been trawling around my basement recently and found that a lot of my duct connections have exceeded my wildest dreams of what poor craftsmanship looks like. Lots of connections were "sealed" using literal duct tape - which has since crusted off and is not holding on to anything. The joints where circular ducts attach to box ducts are the worst offenders.

Thanks for your time.

Answers 2

Duct mastic or metal tape is the recommended method for sealing forced air supply ducts. All the cool kids are using mastic these days.

February 17, 2016 01:56 AM

If your question is about the air ducts, why not use the correct material for the job, rather than silicone caulk. Duct sealant...

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RISE Duct Seals are a multi-cable and pipe transit sealing system providing an effective and simple solution to all fire, gas and water tight duct sealing requirements:

RISE Duct Seals provide high elasticity and bonding strength which resists movement, shock and vibration providing a stable duct seal. RISE rubber insert sleeves are applied to provide cable separation and a backing for the application of the FIWA sealant. 60mm RISE sleeves are adequate for water and gas tight duct sealing.

CSD RISE Cable Duct Seal System is ATEX, WIMES, ESI, DSEAR, National Grid, Network Rail, MOD, Highways Agency (Series 1500) and Lloyds Shipping accepted for utilities, oil, gas, petrochem, rail, construction, street lighting, power industry and hazardous area applications.

CSD RISE cable duct sealing kits provide an effective and simple solution for all gastight, watertight and fireproof duct sealing requirements - ideal for triplex...

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Ducts that run through cellars, attics, and crawlspaces are an integral part of a forced-air heating or cooling system and their purpose is to circulate air to evenly heat and cool your home. Unfortunately, ducts are often leaky – wasting a fifth or more of the heating and cooling energy used by your home. And the answer is: NOT DUCT TAPE!

How to tell if ducts need repairs

Rooms are too warm or too cold High summer and winter utility bills Little or no air flow from registers in some rooms Air filter gets dirty quickly – needs to be changed more than once a month – indicating leaks in return ducts. Streaks of dust at registers or duct connections No insulation on visible ducts (those in an attic or crawl space) Flexible ducts are tangled or kinked

How to seal duct leaks

Is duct sealing something you can do yourself?

If your ducts are easily...
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4 offers 4,882 silicone duct products. About 15% of these are hvac systems & parts, 6% are rubber hoses, and 4% are adhesives & sealants. A wide variety of silicone duct options are available to you, such as free samples, paid samples. There are 4,926 silicone duct suppliers, mainly located in Asia. The top supplying countries are China (Mainland), Taiwan, and India, which supply 99%, 1%, and 1% of silicone duct respectively. Silicone duct products are most popular in Domestic Market, Mid East, and Southeast Asia. You can ensure product safety by selecting from certified suppliers, including 2,027 with ISO9001, 1,246 with ISO14001, and 1,057 with Other...
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Older, less-efficient furnaces used to be vented via an exhaust pipe running to a chimney. Modern furnaces are so energy-efficient that much of the heat that was once vented up through a chimney is recaptured and used to heat the house. Because of this, virtually all modern energy-efficient furnaces are now vented through a PVC or metal pipe that leads directly out of the side of the foundation. These vents need to be sealed to prevent air drafts, water leaks and even insects from getting inside of your home. Use silicone caulk to seal gaps up to about 1/4 inch; foam sealant will take care of anything larger than that.

Using Silicone Caulk

Brush away any dirt or dust from the area around the furnace vent that you will be sealing.

Cut the tip of a caulk tube with a utility knife. Some caulk guns have built-in tube cutters that work like a scissors on the handle. Load the tube into the caulk gun.

Inject the silicone caulk into the gap between the vent...

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Most residential duct systems have numerous leaks that waste energy and lead to room-to-room pressure imbalances. Unfortunately, though, few building inspectors outside of California bother to enforce existing code requirements that residential duct seams be sealed with mastic or high-quality duct tape.

Most model codes, including the International Residential Code (IRC), include duct tightness provisions:

The 2006 IRC section N1103.2.2 requires that “Ducts, air handlers, filter boxes and building cavities used as ducts shall be sealed,” while IRC section M1601.3.1 requires that “Joints of duct systems shall be made substantially airtight by means of tapes, mastics, gasketing or other approved closure systems.” Hardware-store duct tape is not an approved tape. Section 403.2.2 of the 2004 International Energy Conservation Code (IECC International Energy Conservation Code.) requires that “All ducts, air handlers, filter boxes, and building cavities used as ducts shall be...
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Duct leakage associated with forced air HVAC systems has proven to be one of the largest energy wasters in our industry. Just like many things in the HVAC business, the devil is in the details in regards to duct sealing. Depending on who you talk to, you could get a number of different answers on the proper way to seal a duct system. There are a lot of different tools, materials, methods, and testing that contractors are using to seal ducts.

What gear do I really need to seal ducts?
The type of sealant you plan on using for patching all those holes is going to have a large impact on the gear you will need.For UL 181 rated tapes, you're going to need some good rags for cleaning the duct material off, and a squeegee for smoothing out those taped joints.

If applying a water based mastic to a duct system, you're going to need an old set of clothes or coveralls, a set of gloves (I like Kevlar) and a hat to get started. Eye protection, different width paint...

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I'm getting ready to assemble some ductwork. Advice from an HVAC relative is to use silicone caulk to seal takeoff collars, duct joints, etc. Everything I read here references mastic/mesh and/or UL181 tape.
What would best practice be? If mastic, is the stuff available at home centers good, or do I need to go to an hvac supply house?
thanks! Well, let me be the 1st to say "you should have called a pro". Be prepared to hear that about a dozen more times.

Ok, enough sarcasm... I'd go with mastic (aka pooky). Silicone is somewhat messy (at least when I put it on), some of it can really stink, and it's somewhat time consuming to put on.

Mastic gets smeared on with a cheap paint brush, doesn't really smell and cleans up with water.

About the only time I use caulking to seal duct is if it's going to be exposed in some fancy building (mostly commercial). If it's in a residential setup and exposed, I still pooky.

What kind of Duct is...
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10 duct sealant,k...

Industrial & Scientific. Adhesive Tapes; Industrial Sealants; Industrial Joint Sealants; Duct Tape; High Temperature Tape + See more; Tapes, Adhesives & Sealants

Water Based Mastic Half Gallon Tub - The Home Depot

Sealing air duct plenums, takeoffs, elbows, and vent boots where they connect and sealing the seams, per product instructions, may help save energy. The sealant is fiber reinforced and easy to apply by brush, gloved hand, or putty knife to flex duct, duct board, and sheet metal air ducts.

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

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

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