---
product_id: 11466289
title: "Deflecto Duct Increaser and Reducer, Plastic Inline Adapter, White, 4” to 3” (IRB43)"
price: "$19.53"
currency: USD
in_stock: true
reviews_count: 8
url: https://www.desertcart.us/products/11466289-deflecto-duct-increaser-and-reducer-plastic-inline-adapter-white-4
store_origin: US
region: United States of America
---

# 4" to 3" transition Durable up to 325°F Easy installation Deflecto Duct Increaser and Reducer, Plastic Inline Adapter, White, 4” to 3” (IRB43)

**Price:** $19.53
**Availability:** ✅ In Stock

## Summary

> 🔧 Transform Your Duct Game!

## Quick Answers

- **What is this?** Deflecto Duct Increaser and Reducer, Plastic Inline Adapter, White, 4” to 3” (IRB43)
- **How much does it cost?** $19.53 with free shipping
- **Is it available?** Yes, in stock and ready to ship
- **Where can I buy it?** [www.desertcart.us](https://www.desertcart.us/products/11466289-deflecto-duct-increaser-and-reducer-plastic-inline-adapter-white-4)

## Best For

- Customers looking for quality international products

## Why This Product

- Free international shipping included
- Worldwide delivery with tracking
- 15-day hassle-free returns

## Key Features

- • **Lightweight Design:** Weighing only 0.8 ounces, it's easy to handle and install.
- • **Durable Polypropylene:** Built to last with a high melting point of 325°F.
- • **Versatile Applications:** Perfect for bathroom fans and dryer exhausts.
- • **Seamless Duct Transition:** Effortlessly connect 4" and 3" ducts for a perfect fit.
- • **User-Friendly Installation:** Simply slip and tighten with clamps for a secure connection.

## Overview

The Deflecto Duct Increaser and Reducer (Model IRB43) is a lightweight, durable plastic inline adapter designed to seamlessly transition between 4" and 3" diameter ducts. Ideal for bathroom fan installations and dryer exhausts, it ensures a secure fit with easy installation, making it a must-have for any home improvement project.

## Description

Product Description Adapt your 3” duct to a 4” exhaust hood with the Deflecto Duct Increaser and Reducer. This polypropylene plastic connector is an ideal connector when installing bathroom fans as well. Slip the ducts over the ends of the increaser/reducer, and tighten down with clamps (not included). Durable and lightweight, this reducer has a melting point of approximately 325 degrees F. Deflecto was founded on innovative, problem solving products. For over a half century, we have built a tradition of discovering and meeting needs with invention and dependable manufacturing. Today, Deflecto is the world’s largest chair mat, bicycle reflector and dryer venting manufacturer and a global leader in sign and literature holders, office workspace accessories and other air distribution products. From the Manufacturer Deflecto Irb43 Plastic Reducer 4 inch To 3 inch ; Allows Use Of 4 inch Exhaust Hood With 3 inch Duct; Plastic Material allows for light weight design

Review: Does the job - Used to decrease 4 to 3 inch exhaust fan duct. Perfect.
Review: Works fine if you hot glue it - As others have said the 4 inch side is the same size as the 4" outlet duct on newer bathroom vent fans BUT I used a hot glue gun to essentially "weld" the two plastic pieces together. To assure a strong connection I wrapped the joint afterward with silicone self adhesive tape. I imagine duct tape would also work. The existing 3" flexible duct was a snug fit, but with a little effort it went over the 3" side of the reducer. I considered using a galvanized steel 3x4 duct adapter (Home Depot, Menards) but because of all the shower moisture being vented out I was concerned with the piece rusting over time. The plastic reducer was cheaper and will be rust-free.

## Features

- Designed to transition between 4" and 3" diameter ducts
- Simply slip the ducts over the increaser/reducer, tightening in place with clamps (not included)
- Durable polypropylene construction has a melting point of approximately 325 degrees
- Connects a 4 inch dryer exhaust hood to a 3 inch duct
- Ideal for bathroom fan installations

## Technical Specifications

| Specification | Value |
|---------------|-------|
| Brand Name | Deflecto |
| Model Info | IRB43 |
| Item Weight | 0.8 ounces |
| Product Dimensions | 4 x 3.4 x 4 inches |
| Item model number | IRB43 |
| Is Discontinued By Manufacturer | No |
| Part Number | DEFIRB43 |
| Special Features | Lightweight |
| Color | White |
| Connector Type | Reducer |
| Material Type | Plastic |
| Included Components | Deflecto Duct Plastic Increaser and Reducer |
| Batteries Included? | No |
| Batteries Required? | No |

## Images

![Deflecto Duct Increaser and Reducer, Plastic Inline Adapter, White, 4” to 3” (IRB43) - Image 1](https://m.media-amazon.com/images/I/71ynkr5cqxL.jpg)

## Customer Reviews

### ⭐⭐⭐⭐⭐ Does the job
*by R***A on January 12, 2026*

Used to decrease 4 to 3 inch exhaust fan duct. Perfect.

### ⭐⭐⭐⭐⭐ Works fine if you hot glue it
*by A***I on May 22, 2018*

As others have said the 4 inch side is the same size as the 4" outlet duct on newer bathroom vent fans BUT I used a hot glue gun to essentially "weld" the two plastic pieces together. To assure a strong connection I wrapped the joint afterward with silicone self adhesive tape. I imagine duct tape would also work. The existing 3" flexible duct was a snug fit, but with a little effort it went over the 3" side of the reducer. I considered using a galvanized steel 3x4 duct adapter (Home Depot, Menards) but because of all the shower moisture being vented out I was concerned with the piece rusting over time. The plastic reducer was cheaper and will be rust-free.

### ⭐⭐⭐⭐ Worked as described.
*by D***G on April 8, 2025*

Worked as described. Was used to convert a 3in bathroom exhaust to a 4in. Pretty straight forward item.

## Frequently Bought Together

- Deflecto Duct Increaser and Reducer, Plastic Inline Adapter, White, 4” to 3” (IRB43)
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*Product available on Desertcart United States of America*
*Store origin: US*
*Last updated: 2026-02-21*