A combi boiler vertical flue must be a manufacturer-approved venting system matched to the boiler model—not a fireplace or wood-stove chimney accessory. The products supplied for this article are mostly decorative flue stops, a masonry chimney cap, and a stove replacement part; none is identified as a combi boiler vertical flue kit. The comparison below explains what each item is described for and why buyers should verify compatibility before purchasing. For a boiler installation, start with the boiler’s installation manual and an appropriately qualified heating professional.
| Product | Listed use or feature | Boiler-flue fit |
|---|---|---|
| LKQI 3F-72 Flue Stop | Adjustable fireplace or stove flue opening cover | Not identified as boiler venting |
| Imperial 6719900 Flue Stopper | Decorative chimney plug | Not identified as boiler venting |
| Draft King SS2020U Cap | Cap for specified masonry flue dimensions | Not suitable for metal chimney; not identified as boiler venting |
| Imperial BM0026 Flue Stop | Adjustable flue stop | Features provide little application detail |
| US Stove Collar Weld Tab | Stove flue-collar attachment part | Not identified as boiler venting |
LKQI 3F-72 Adjustable Flue Stop
The LKQI 3F-72 is described as a fireplace stove-pipe flue-hole cover, not as a boiler flue terminal or vent component. Its listed features include a 9 5/8-inch diameter, an adjustable range of 4 to 10 inches, a backside adjustable bar, and painted galvanized steel.
Best for: Buyers looking for an adjustable cover for a compatible fireplace or stove flue opening. It was selected because it is the only listed product with a stated broad adjustment range. Limitation: The supplied details do not establish boiler compatibility. Do not use it to terminate or modify a combi boiler flue.
Imperial 6719900 Adjustable Flue Stopper
This black Imperial stopper adjusts for 6-, 7-, and 8-inch flue-wall openings. The product details say it has an adjustable spring for a snug fit and is used as a decorative plug for wood-stove chimneys and vent stacks.
Best for: A buyer who needs a decorative plug for an opening within the stated size range and application. It was selected because its dimensions and decorative purpose are specified. Limitation: A decorative chimney plug is not described as a working boiler vent part. Avoid using it on an active boiler flue.
Draft King SS2020U Stainless Steel Chimney Cap
The Draft King SS2020U is specified for masonry flues and fits outside tile dimensions from 18.5 by 18.5 inches to 20.25 by 20.25 inches. Its listed construction includes a stainless steel hood, expanded-metal mesh, and slotted mounting bolts. The manufacturer details explicitly say it is not suitable for a metal chimney.
Best for: Buyers assessing a cap for a masonry chimney within the stated tile dimensions. It was selected because its mounting application and size range are clearly described. Limitation: It is a chimney cap, not a listed combi boiler vertical flue terminal. Its masonry application also rules it out for metal chimneys.
Imperial BM0026 Adjustable Flue Stop
The supplied listing identifies this item as an Imperial adjustable flue stop, model BM0026. Although the product name includes a cream color, the feature text calls it a black adjustable flue stop. The listing does not provide a size range or detailed installation information in the supplied features.
Best for: Buyers researching an adjustable flue stop who can confirm the model and fit from the complete product information. It was selected as another listed adjustable stop, but the available details are limited. Limitation: Color and application information are inconsistent, and no boiler compatibility is stated. Confirm details before buying and do not treat it as a boiler flue component.
US Stove Flue Collar Weld Tab
This listing describes an OEM US Stove flue collar weld tab, part 83431, which replaces part 80314. Its stated role is to hold a flue collar to a stove body. The supplied feature information does not give dimensions or identify a boiler application.
Best for: Someone checking a replacement part for a compatible US Stove assembly and confirming the part number against the appliance documentation. It was selected because it relates to a flue connection, although it is a stove component rather than a complete flue. Limitation: It is not described as a combi boiler vent part; verify the appliance and part number before ordering.
Buying Guide: How to Choose a Combi Boiler Vertical Flue
What should a boiler vertical flue include?
Look for a complete venting system specifically approved for the exact boiler model. Depending on the appliance and installation, the system may require compatible flue sections, bends, seals, supports, and an external terminal. Do not assume that a part described for a fireplace, stove, masonry chimney, or generic vent stack can be used on a boiler.
How do you confirm compatibility?
Check the boiler’s model and installation manual, then compare the specified flue type, diameter, permitted components, and installation arrangement with the part documentation. If a listing does not explicitly establish compatibility, treat that as unconfirmed. Ask the boiler manufacturer or a qualified heating professional when the documentation is unclear.
What should you check for a vertical route?
Confirm that the boiler permits a vertical flue arrangement and follow its instructions for routing, termination, clearances, and any required accessories. The allowed route and terminal position vary by appliance and installation. A chimney cap or flue stopper is not a substitute for the specified boiler terminal.
Which listed product is closest to a boiler flue part?
None of the five products is identified as a combi boiler flue kit or approved boiler terminal. The US Stove weld tab is an appliance attachment part, while the other listings are flue stops or a masonry chimney cap. Their descriptions do not support using them in a boiler exhaust system.
Frequently Asked Questions
Can a fireplace flue stopper be used on a combi boiler?
Not based on the information provided. The listed stoppers are described for fireplace, wood-stove, or decorative chimney applications, not as boiler vent components.
Does a vertical combi boiler flue need a special terminal?
Use the terminal and components specified for the boiler model and installation. Check the appliance manual rather than substituting a general chimney cap.
Can the Draft King cap fit a boiler flue?
The listing describes it for specified masonry tile flues and says it is not suitable for metal chimneys. It does not identify a combi boiler application.
What information should I have before buying a boiler flue?
Have the boiler make and model, the manual’s flue requirements, the intended route, and the required component specifications available. Confirm uncertain details with the manufacturer or a qualified professional.
Are these products a complete vertical flue system?
No. The supplied descriptions do not identify any of them as a complete combi boiler vertical flue system.