Advice for homeowners


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Harry works for a FENSA Approved installation company. He's on a mission to help professionalise installers and protect homeowners across the UK, so he started this advice column.

Combustion Ventilation - Don't Get Caught Out

Mention gas appliances and installers usually shrug their shoulders and say it is nothing to do with them. They could not be more wrong! There are a couple of instances where not taking notice of a flue or vent may land you with a failed inspection, or even worse, a trip to court.




First up is the combustion vent. This is a vent that is permanently open and usually looks like a plastic cone on the glass with a free spinning fan inside. Sometimes they are vents that were once closable, but a gas engineer may have removed the cords long ago. This vent needs to be permanently open so the appliance can get enough oxygen to burn efficiently. If it does not burn efficiently then it will produce too much carbon, which will soot up flues leading to a blockage.

If not spotted this could result in carbon monoxide spilling back into the property, with possibly deadly effects. These vents are only used when the appliance takes its oxygen from within the room, such as back boilers. Modern balanced flue boilers do not need them. If the old boiler has been removed and a new room-sealed appliance installed, then you can take away that permanently open vent and replace it with a new solid piece of glass.

Unless you are completely confident you can proceed, you must always seek confirmation from a gas safe engineer. Ignorance is no defence in law.




Next for discussion are the flues themselves. Flues have usually been installed to the regulations that were applicable at the time. They would have been positioned away from openings so the exhaust gases do not immediately flow back into the building. For window installers to comply, they must not move any opening closer to the flue than is acceptable under the current regulations. Where installers seem to get caught out is in buildings constructed in the 1980s and 1990s where the boiler was installed in the corner of the kitchen next to a window.

The window is usually a fixed pane next to the boiler with a side hung opposite. At the time of the sale of replacement windows, the householder explains that they cannot easily reach the window to close it as the handle is halfway up the opener. A decision is then made to convert the window from a half side hung to a full top hung. This is great for closing the window, but you have just moved the opener right next to the flue - this does not satisfy current regulations!

Remember if in any doubt about gas appliances you can consult Approved Document J (available as a free download on the Planning Portal website) as this will give you correct distances from a flue as well as minimum ventilation requirements. An even safer bet is to talk to a gas engineer.


Boiler Flue Regulations


All of these things fall under the boiler flue regulations. Regulations like these cover the use and flow of gas around your home. By following these rules, you ensure that no harmful gases from your combustion ventilation system can flow back into your home, potentially causing damage. Because most boilers, such as gas, system and combi boilers have flues, you'll most likeky need to follow boiler flue regulations.


If you're planning to install new windows or a new boiler, its important noto have them be too close together. If a flue is within 30-60cm of a window or even a door, it will fall foul of the regulations. It's because, athat distance, you won't be able to guarantee the gases coming from your flue won't come back into your home. Although these rules are for horizontal flues, you can also get vertical flues. You should have it encased for aesthetics, but you must make sure there are access points in the design.


Combustion Ventilation with FENSA


If you wanto meet boiler flue regulations with your combustion ventilation system, its importanto work with the right people. If you fit new flues yourself, there's a chance you can get caught out. However, when you work with a FENSA installer, you won't have to worry abouthe regulations. Instead, you'll work with trained experts who know boiler flue regulations back to front, helping to make your home's ventilation legal and compliant.


FENSA installers can help you if you're installing a new boiler, or choosing to move an old one. In either case, your installers will be qualified to complete the task. You shouldn'trust anybody else to complete this work, either; FENSA installers have the required legal certification to move and install boilers in the UK. When you find a FENSA installer, then, you can be sure that your boiler will be above board.


You can search through our website today for advice on combustion ventilation, and to take a look at our certificates. And, if you need to find a FENSA Approved Installer today, use our site to search for ones in your local area. We make combustion ventilation safer at FENSA!

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What to check before appointing an installer

Check that you use a FENSA Approved Installer but also check the following:

  • Ask family and friends who have used installers about their satisfaction and whether they got a FENSA certificate.
  • Check the installer's references by talking to their previous customers.
  • Get at least three quotes and check you are being quoted like for like.
  • Cheapest is not always best and good contractors are always in demand.
  • Get quotes, timeframes and the fact that you will get a FENSA certificate all in writing. A proper written contract with an agreed completion date will help prevent confusion later on
  • Check the warranty on the installer's work and ensure they have enough insurance to cover their warranty. Domestic glazing installers that are registered with a competent person scheme like FENSA are legally obliged to provide warranty insurance to cover your installation should the company cease to trade within the life of the warranty.
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