Screw-FIX Increaser - Ø 125-150mm
At a Glance
- 316L Stainless Steel Construction
- Increases flue diameter from 125mm to 150mm
- Fully compliant with Building Regulations Document J
- Suitable for multiple fuel types: wood, gas, oil, smokeless coal
- Designed for seamless connection with MI-FLEX flexible flue liners

We Won't Be Beaten On Price
At National Flues, we continuously monitor competitor prices. This ensures that we consistently offer you the best deals on all our products. Here’s how we keep your costs low:
- Daily Price Matching: Our team adjusts prices to ensure we stay competitive.
- Bulk Purchasing Power: We sell a lot, so we can negotiate better rates with suppliers, passing the savings directly to you.
- Operational Efficiency: We have streamlined processes to reduce overhead.
Price Match Guarantee: If you find the same product cheaper within 48 hours, we’ll match it and refund the difference.
Free Delivery Over £100: Orders over £100 are free delivery (call us if delivery is required outside the mainland UK).
“I saved 20% on my purchase compared to other retailers. Exceptional service!” – Jane D.
Have Questions?
Phone: 01670 206999
Email: [email protected]
- Info
- Specs
- Install
- FAQs
The Screw-FIX Increaser Ø 125-150mm is a high-quality 0.6mm 316 stainless steel adaptor designed for connecting a rigid single wall flue system to a MI-FLEX flexible flue liner. Specifically meant to facilitate a seamless transition, it increases the diameter from 125mm to 150mm. The increaser is especially designed for use with MI-FLEX 316 and 904 multi-fuel flexible flue liners, making it integral to a complete chimney system.Adhering to Building Regulations Document J, this fitting can only be installed within a masonry chimney, ensuring safety and compliance.
It is suitable for various fuel types, including wood (with moisture content below 20%), smokeless coal, gas, and oil, and can withstand temperatures up to 600°C (T600 designation). The installation mandates that the bottom fixing be secured properly to ensure a gas-tight seal, with the use of fire cement, ceramic rope or tape, or high-temperature sealant recommended.For efficient maintenance and longevity of your chimney system, ensure regular sweeping by a competent person, ideally a HETAS registered sweep for solid fuel applications. It's crucial to check the chimney system twice a year, before and after the heating season, to avoid blockages and buildup of deposits like bird nests.
SKU: 25-125-MR
Technical Specifications | |
---|---|
Material | 316L Stainless Steel |
Diameter Increase | 125mm to 150mm |
Temperature Tolerance | Up to 600u00b0C |
Design Standard | BSEN 1856-2 T600 N1 W V2 L50012 G |
Suitable For | Wood (moisture <20%), Gas, Oil, Smokeless Coal |
System Compatibility | MI-FLEX Accessories MF20 |
Installation | Within masonry chimneys in line with Building Regulations Document J |
Delivery Information +
We work relentlessly to ensure you get your order fast. Estimated delivery for this product is Thursday, April 3rd. If you need faster stove or fireplace delivery please give us a call. We can often reduce longer lead times if we pay the carrier £25 for express delivery. Visit our Shipping Information page for more information.
Warranty & Returns +
All our products come with warranties. Mi-Flex offers a lifetime guarantee. Returns for damaged items are covered by insurance; non-damaged returns incur return delivery costs.
Price Match Guarantee +
We will match any price like for like. If you find it cheaper within 48 hours, we'll refund the difference.
Compatible and other products that may be of interest...
National Flues Ltd Verdict
At National Flues, the Screw-FIX Increaser Ø 125-150mm is a must-have for any chimney system utilising MI-FLEX flexible flue liners. Its robust design ensures a perfect fit and reliable performance, accommodating various fuel types. We deliver this excellent product nationwide to both retail and trade customers.
The Screw-FIX Increaser is designed to connect and increase the diameter of a rigid single wall flue system to an MI-FLEX flexible flue liner, facilitating a robust and seamless transition within a chimney system.
National Flues is a trusted supplier of high-quality fireplaces and flue components across the UK, serving both retail and trade customers with unbeatable prices and reliable delivery services.
