---
product_id: 41959850
title: "0841DX F-Seal 181 Duct Seal, Fiber Reinforced Water Based Duct Sealant, 1 Gallon, Gray, Made in USA"
brand: "red devil"
price: "57431CFA"
currency: XOF
in_stock: true
reviews_count: 8
category: "Red Devil"
url: https://www.desertcart.sn/products/41959850-0841dx-f-seal-181-duct-seal-fiber-reinforced-water-based
store_origin: SN
region: Senegal
---

# Exceeds SMACNA Pressure & Sealing Classes Weather-resistant for indoor/outdoor use UL 181 A-M & B-M certified 0841DX F-Seal 181 Duct Seal, Fiber Reinforced Water Based Duct Sealant, 1 Gallon, Gray, Made in USA

**Brand:** red devil
**Price:** 57431CFA
**Availability:** ✅ In Stock

## Summary

> 🔧 Seal smart, save energy, and stay ahead of the HVAC game!

## Quick Answers

- **What is this?** 0841DX F-Seal 181 Duct Seal, Fiber Reinforced Water Based Duct Sealant, 1 Gallon, Gray, Made in USA by red devil
- **How much does it cost?** 57431CFA with free shipping
- **Is it available?** Yes, in stock and ready to ship
- **Where can I buy it?** [www.desertcart.sn](https://www.desertcart.sn/products/41959850-0841dx-f-seal-181-duct-seal-fiber-reinforced-water-based)

## Best For

- red devil enthusiasts

## Why This Product

- Trusted red devil brand quality
- Free international shipping included
- Worldwide delivery with tracking
- 15-day hassle-free returns

## Key Features

- • **Seal Like a Pro:** Fiber-reinforced formula ensures leak-proof HVAC systems, boosting energy efficiency and cutting costs.
- • **Fast & Safe Application:** Low VOC, quick-drying formula means less downtime and safer use in sensitive environments—perfect for modern green buildings.
- • **Certified HVAC Perfection:** UL 181 A-M & B-M certification guarantees compatibility with all duct types—metal, fiberglass, and flexible.
- • **Built to Brave the Elements:** Weather-resistant and mold-proof, this sealant thrives indoors and outdoors, maintaining integrity under UV and moisture exposure.
- • **Made in the USA, Trusted Worldwide:** Proudly crafted in the USA, surpassing industry standards for pressure and sealing performance.

## Overview

Red Devil 0841DX F-Seal 181 is a premium, fiber-reinforced, water-based duct sealant designed for superior HVAC sealing. UL 181 A-M & B-M certified, it works on metal, fiberglass, and flexible ducts. Its fast-drying, low VOC formula is weather-resistant and mold-proof, suitable for indoor and outdoor use. Exceeding SMACNA standards, this 1-gallon gray sealant is made in the USA to ensure durable, energy-efficient HVAC performance.

## Description

Red Devil F-Seal 181 is a premium fiber-reinforced water-based duct sealant engineered for superior performance in all HVAC systems. This versatile sealant is UL 181 A-M & B-M certified, making it suitable for metal, fiberglass, and flexible ducts. Its fast-drying, low VOC formula ensures quick application and safety in sensitive environments. F-Seal 181 exceeds all SMACNA Pressure and Sealing Classes, providing unmatched sealing capabilities for high, medium, and low-pressure HVAC systems. The durable, weather-resistant formula is perfect for both indoor and outdoor use, resisting mold, mildew, and UV damage. It contributes to LEED EQ Credit 4.1 and meets CA Dept. of Public Health Emission Requirements V1.1, 2011. This USA-made product offers excellent adhesion, flexibility, and can be painted after full cure. For best results, apply in temperatures between 40°F and 110°F, allowing 24-72 hours drying time before pressure testing. F-Seal 181 is your go-to solution for efficient, long-lasting HVAC duct sealing.

Review: Thick and goes a long way - Used this to seal various parts of my air conditioning system. I applied to seams and screws on the air handler in the attic and also to all connections of the flex duct from the sheet metal plenum. The goal was to reduce as much air loss as possible. I removed the flex duct that was held on with duct tape and a screw. It was all installed around 35 years ago and I found old instructions that said to use duct tape which of course today you are not supposed to use duct tape for anything HVAC anymore. I used an old 2" paint brush. You really want one with stiff bristles because this stuff is thick maybe closer to joint compound consistency. I spread everywhere around each start collar really pushing the sealant into the cracks and leaving a thick layer. I put a liberal glob over any screwheads and spread across any places air might pass through such as seams. It was dry enough within an hour to not be pliable anymore but full cure says 24-48 hrs. For me, I was able to do the second coat for most except the thicker spots. I poured a little water into the jug which thinned it so I could get a better spread over the thicker parts and feather out the product. I was working in a hot attic and I found having a separate container with just water helped a lot since leaving the lid off obviously dries it out. Adding water back in seemed to restore even the drier bits along the sides of the jug. I used a putty knife to scrape it back in and it mixed back in to the rest of it easily. I assume after a full cure it no longer accepts water and creates a permanent moisture proof barrier. Otherwise what's the point. I also spread some on the neck of the start collar and then inside the duct so that when I slid the flex duct back over there would be a seal. This is what you're supposed to do. I then put a screw back in to secure the two together. You're not supposed to do that though, you're supposed to use a zip tie and tensioning tool but I didn't feel like spending the money on those things was necessary since the screws held fine all this time. I used paper backed, pressure sealing foil tape to wrap the flex duct and seal it to the collar. Using pressure you get a great seal so no air can get in or out. Another coating of this mastic over the taped edges and I was set. Simply pull the fiberglass back over the collar and against the plenum then pull the outer vapor layer over the insulation to the plenum and I was done. I also redid a bunch of the flex connections to the boots. The boots had riveted edges which could easily pass air through so I spread over all corners inside or out. I have a 5 ton system and with everything I did there is still half of the container left. I liked the white color because I was able to use it on the ceiling diffusers to seal any cracks without worry about the color. I don't know what else this stuff can be used on but I'm going to find out.
Review: Nice thick sealant easily applied with brush and easy to clean up since water based. - I needed a duct sealant for the A/C intake air box. The edges of the air box had separated and were in need of repair to keep contamination out. I initially had some flexible strips to close the crack and then sealed it thoroughly with the duct sealant. Nice and think, but still easily applied with a paint brush. Since it is water based, I was able to clean the brush (and myself!) with just water.

## Features

- SUPERIOR SEALING: Fiber-reinforced formula ensures leak-free HVAC systems, improving energy efficiency and performance
- VERSATILE APPLICATION: UL 181 A-M & B-M certified for use on all types of HVAC ductwork, including metal, fiberglass, and flexible ducts
- INDOOR/OUTDOOR DURABILITY: Weather-resistant sealant withstands various conditions, making it ideal for both interior and exterior use
- FAST-DRYING & LOW VOC: Quick application and reduced drying time, with low volatile organic compounds for safer use in sensitive environments
- EXCEEDS INDUSTRY STANDARDS: Surpasses all SMACNA Pressure and Sealing Classes, ensuring top-quality performance for your HVAC systems

## Technical Specifications

| Specification | Value |
|---------------|-------|
| Brand | Red Devil |
| Item Weight | 1 Pounds |
| Item dimensions L x W x H | 7 x 7 x 8 inches |
| Material | Acrylic |
| Style | 1 - Pack |
| Water Resistance Level | Water Resistant |

## Product Details

- **Brand:** Red Devil
- **Item Weight:** 1 Pounds
- **Item dimensions L x W x H:** 7 x 7 x 8 inches
- **Material:** Acrylic
- **Style:** 1 - Pack

## Images

![0841DX F-Seal 181 Duct Seal, Fiber Reinforced Water Based Duct Sealant, 1 Gallon, Gray, Made in USA - Image 1](https://m.media-amazon.com/images/I/718Qkc+7HiL.jpg)

## Available Options

This product comes in different **Color, Size, Style** options.

## Questions & Answers

**Q: Is the "F" in the bucket like a liquid (brushable) or more like a paste?**
A: It's not quite like a paste but it's not liquidity either and doesn't drip so you can put it on thick.  I love this stuff, not much of a odor as well. I used a cheap chip brush to spread it.

**Q: I'm redoing all the flex ductwork (insulated kind) in a crawl space. should i use the d our f sealant ?**
A: You could use either one.  Both are perfect for what you are doing, but I would use the F-Seal because it has fibers in it.

**Q: Is this safe to use and will it work on gas dryer duct work joints (inside the fittings and outside)?**
A: Sorry, this should not be used on a dryer. It is for HVAC only. Thanks.

**Q: How long do I need to wait before turning on the A/C after application?**
A: Hi, you should wait 24 hours. Thanks....

## Customer Reviews

### ⭐⭐⭐⭐⭐ Thick and goes a long way
*by S***R on July 30, 2024*

Used this to seal various parts of my air conditioning system. I applied to seams and screws on the air handler in the attic and also to all connections of the flex duct from the sheet metal plenum. The goal was to reduce as much air loss as possible. I removed the flex duct that was held on with duct tape and a screw. It was all installed around 35 years ago and I found old instructions that said to use duct tape which of course today you are not supposed to use duct tape for anything HVAC anymore. I used an old 2" paint brush. You really want one with stiff bristles because this stuff is thick maybe closer to joint compound consistency. I spread everywhere around each start collar really pushing the sealant into the cracks and leaving a thick layer. I put a liberal glob over any screwheads and spread across any places air might pass through such as seams. It was dry enough within an hour to not be pliable anymore but full cure says 24-48 hrs. For me, I was able to do the second coat for most except the thicker spots. I poured a little water into the jug which thinned it so I could get a better spread over the thicker parts and feather out the product. I was working in a hot attic and I found having a separate container with just water helped a lot since leaving the lid off obviously dries it out. Adding water back in seemed to restore even the drier bits along the sides of the jug. I used a putty knife to scrape it back in and it mixed back in to the rest of it easily. I assume after a full cure it no longer accepts water and creates a permanent moisture proof barrier. Otherwise what's the point. I also spread some on the neck of the start collar and then inside the duct so that when I slid the flex duct back over there would be a seal. This is what you're supposed to do. I then put a screw back in to secure the two together. You're not supposed to do that though, you're supposed to use a zip tie and tensioning tool but I didn't feel like spending the money on those things was necessary since the screws held fine all this time. I used paper backed, pressure sealing foil tape to wrap the flex duct and seal it to the collar. Using pressure you get a great seal so no air can get in or out. Another coating of this mastic over the taped edges and I was set. Simply pull the fiberglass back over the collar and against the plenum then pull the outer vapor layer over the insulation to the plenum and I was done. I also redid a bunch of the flex connections to the boots. The boots had riveted edges which could easily pass air through so I spread over all corners inside or out. I have a 5 ton system and with everything I did there is still half of the container left. I liked the white color because I was able to use it on the ceiling diffusers to seal any cracks without worry about the color. I don't know what else this stuff can be used on but I'm going to find out.

### ⭐⭐⭐⭐⭐ Nice thick sealant easily applied with brush and easy to clean up since water based.
*by P***L on October 17, 2025*

I needed a duct sealant for the A/C intake air box. The edges of the air box had separated and were in need of repair to keep contamination out. I initially had some flexible strips to close the crack and then sealed it thoroughly with the duct sealant. Nice and think, but still easily applied with a paint brush. Since it is water based, I was able to clean the brush (and myself!) with just water.

### ⭐⭐⭐⭐⭐ Worked great for me
*by O***D on April 28, 2025*

Background, my attic was a horror show. Duct insulation that had been pinned on with 4" nails by some insane attic seamstress. Vents were uninsulated. Bare ductwork metal in too many places to count. I could go on at length, but you'll have to wait for the book. Bucket arrived in good shape. Shipping was good, then it was delayed, then it was delivered. Some of the other items in the box had a little mastic on them but the bucket I got looked pristine, unleaked, and had 2 lengths of sturdy tape holding the lid on. Mastic inside was not dried or disturbed. I have to wonder if their initial try showed the folly of shipping buckets rattling around in a box. But I digress! Simply put my order of grey goop arrived in great shape. I had ordered a box of 10 or 12 cheap 'chip' brushes so I could use one for the day and just ditch it. I would tear off old poorly applied duct insulation, mastic all seams and screws of the ductwork on my list for the day, and retreat to places more hospitable to humans until the next day. I would leave the bucket fully resealed in the attic: the handle came off on day one and I couldn't get it back on. Easier to leave it where I'm going to use it next rather than lugging it back and forth. It's springtime in Texas, I have a remote thermometer in the attic, and it hit 140° up there the other day. So yeah, I just let it dry till the sun comes up again, then use duct wrap and sleeves with high quality tape. In my attic that's as dry as it's ever going to be. The temperature had no effect on the mastic still sealed in the bucket. Spreads well, seals well, dries well. I intend to eventually go back deep in the attic and mastic at least the edges of all my tape, working my way back to civilization and the attic stairs. I trust the mastic to secure the tape more than I trust the tape not to curl over the years. I wear cheap painter's coveralls and surgical gloves as the mastic, and everything else, tends to get quite snuggly with me. My roof comes down to the soffit on all sides so I'm an old man crawling across the joists and some places can sit up. I still come down looking like a coal miner after a double shift but at least most of the mastic is on the ductwork instead of me. It's brutal up there, so I pick my work for the day, let the mastic start drying, and get out while I still can. Oh yes, don't let the AC or heat come on while your mastic is still drying. Don't want to take a chance on displacing the mastic after all your hard work. I have a little over a month until my youngest son visits and we blow in insulation. I'm going to bury everything up there to the extent I won't be able to get in there to do anything. So, everything I'm going to fix had better be done before then. I'm trusting this mastic to last half of forever because I'm going to make it all but inaccessible in June (God help me). My end game is to stop making the electric company rich, and never go in the attic again.

## Frequently Bought Together

- Red Devil 0841DX F-Seal 181 Fiber Reinforced Water Based Duct Sealant, 1 Gallon, Gray, Made in USA
- Pro Grade - Chip Paint Brushes - 12 Ea 2 Inch Chip Paint Brush Light Brown

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*Product available on Desertcart Senegal*
*Store origin: SN*
*Last updated: 2026-02-10*