Air admittance valve buying guide
Updated: 23 October 2026
You are under a bath, or in a loft beside an open soil pipe, trying to stop a gurgle or a smell without ordering the wrong cap. The expensive mistake is the nominal size, the joint, or a US valve whose inches never meet 40 mm UK waste. This air admittance valve buying guide puts those checks before the price. The [air admittance valve comparison](/hub/diy-supplies/air-admittance-valve) is the amazon.co.uk set behind it, with shelf prices from 19 October 2026. Products Compared did not laboratory-test the valves. A qualifying purchase through our links can earn a commission at no extra cost to you.
You are under a bath, or in a loft beside an open soil pipe, trying to stop a gurgle or a smell without ordering the wrong cap.
You are under a bath, or in a loft beside an open soil pipe, trying to stop a gurgle or a smell without ordering the wrong cap. The expensive mistake is the nominal size, the joint, or a US valve whose inches never meet 40 mm UK waste. This air admittance valve buying guide puts those checks before the price. The air admittance valve comparison is the amazon.co.uk set behind it, with shelf prices from 19 October 2026. Products Compared did not laboratory-test the valves. A qualifying purchase through our links can earn a commission at no extra cost to you.
Our top picks
| Badge | Product | Pipe size | Joint | Standard stated | Note | Price | Offer |
|---|---|---|---|---|---|---|---|
| Best overall |  FloPlast FloPlast AF110G Push-Fit Air Admittance Valve - Grey | 110 mm; size line also Small | Push-fit | BS EN 12380 A1, KM512474 | 9.0 | about £23.85 | View offer |
| Best value |  FloPlast FloPlast AV40 40 mm Compression Air Admittance Valve - White | 40 mm; listing also says 32 mm | Compression | n/a | 7.9 | about £11.38 | View offer |
| Alternative |  FloPlast FloPlast AF32 32/40/50 mm Solvent Weld Air Admittance Valve - White | 32 mm; adaptor 40/50 mm | Solvent weld | BS EN 12380 A1, KM512474 | 8.4 | about £14.99 | View offer |
Alternative
FloPlast FloPlast AF32 32/40/50 mm Solvent Weld Air Admittance Valve - White8.4/10about £14.99
On this page
Stack or branch
Start with the pipe you already have, not with the star rating. A soil stack in a UK house is normally 110 mm. A basin, bath, shower, or washing-machine branch is 32 mm, 40 mm, or 50 mm. A 110 mm valve will not go on a basin pipe, and a 40 mm valve will not finish a soil stack.
Traders often call 110 mm soil 4 inch. That nickname is not a measurement you can order from. The AF110G title is 110 mm push-fit, while the same page prints Small and an outlet of 1.5 inches. A pipe marked 100 mm is not automatically the same socket. Nominal bore is not the outside diameter.
Push-fit, solvent, or compression
The joint decides whether you need solvent cement, a compression nut, or a rubber fin. The FloPlast AF110G is a 110 mm push-fit. Reviews say the rubber fin is tight until you lubricate it, and the instructions do not explain that the seal can come off. The LavaTap 110 mm listing says a female socket takes 110 mm male pipe by push-fit or solvent weld.
The AF32 is solvent weld onto 32 mm, with an adaptor for 40 mm and 50 mm, and the file does not give a cure time. The FloPlast AV40 is compression, sold as 40 mm, and the listing says the socket also fits 32 mm ABS, polypropylene, and MUPVC. Compression is the joint you can undo. The AV40 bullet says it may be used as a secondary rodding point.
What BS EN 12380 and A1 mean for you
BS EN 12380:2002 is the valve standard named in Approved Document H for England and Wales, in Scotland’s domestic Technical Handbook, and in Northern Ireland’s Technical Booklet N. On a box, A1 is trade shorthand. Designation A means the valve may sit below the flood level of the appliances it serves. Designation B means it may not. Class I is −20 °C to +60 °C. FloPlast prints that range as no insulation required.
FloPlast publishes Kitemark licence KM 512474 for AF110, AX110, AV110, AVE100, AF32, and AFE32. In this set only the AF110G and the AF32 state that licence. The AV40 file does not. LavaTap, Oatey, and Operitacx do not state it either. Oatey cites ASSE 1050 and ASSE 1051. Those letters do not answer BS EN 12380. Allowed below the flood level is not permission to fit the valve at any height.
Indoor, height, and what to skip
The valve stays upright, with air around the cap, where you can take it off. FloPlast asks for at least 200 mm above the highest wet entry on a 110 mm valve, and 100 mm on a 32/40/50 mm valve. Approved Document H, clause 1.33, allows an indoor finish in England and Wales, not outside and not in a dust-laden atmosphere. A listing that says internal or external is a product sentence, not that clause.
A boiler air vent, the Operitacx 50/75 pack at £10.69 with no reviews, and the Oatey inch-size valve are the wrong objects here. When size and joint are settled, the best air admittance valve page names the top pick and the best value. Fitting sits on the how to fit an air admittance valve page.
What to write down before you order
Write down 110 mm or 32/40/50 mm, the joint, and whether that listing states BS EN 12380. If the stack is shared, cast iron, or the only vent on a septic tank, use a plumber.
Common questions
Do I need 110 mm or 40 mm?
You need 110 mm when the pipe is the soil stack, and 32, 40, or 50 mm when it is a waste branch from a basin, bath, shower, or washing machine. Measure the nominal size on the pipe, not a guess from the room. A 110 mm valve does not fit a basin, and a 40 mm valve does not finish a stack.
What does A1 on the box mean?
A1 means designation A and temperature class I. A means the valve may sit below the flood level of the connected appliances. Class I, as FloPlast states it, is −20 °C to +60 °C. It is not a score, and it is not a promise that the valve can go outside. Read it, then check whether that exact listing also states BS EN 12380.
Should I choose push-fit, solvent weld, or compression?
Choose the joint that is already on the pipe. Push-fit needs a lubricated rubber fin, solvent weld needs cement and the cure time on the tin, and compression uses a nut you can undo. The AV40 is compression and mentions a secondary rodding point. The AF32 is solvent weld. Mixing them means an adaptor or a cut pipe, not a quicker job.
Can I use a 1.5 inch US valve on 40 mm UK waste?
Not as a match for this pipe. The Oatey Sure-Vent is 1.5 inch to 2 inch with an NPT adaptor, and a UK review says it does not fit 40 mm pipe. ASSE 1050 and ASSE 1051 are the standards on that page, not BS EN 12380. A high review count from the United States does not convert the thread.
Should the valve be allowed outside?
In England and Wales, Approved Document H keeps this valve indoors and out of a dust-laden atmosphere. The BPF Pipes Group note from January 2024 says external use sits outside statutory guidance, except in Scotland under notified-body conditions. A listing that says external is not that guidance. Screened outdoor valves, such as the FloPlast AX110, are a different product and are not in this set.
Related pages
Sources
Public UK sources and the amazon.co.uk listings compared on this page. Listings captured 19 October 2026. Updated 22.10.2026.
- Approved Document H (2015), clauses 1.31–1.33 (retrieved 22.10.2026)
- BPF Pipes Group, Air admittance valves for domestic properties, January 2024 (retrieved 22.10.2026)
- BSI, BS EN 12380:2002 (retrieved 22.10.2026)
- FloPlast soil and waste FAQ (retrieved 22.10.2026)
- FloPlast Kitemark schedule KM 512474 (retrieved 22.10.2026)
- Sefton Council, smelly drains note (retrieved 22.10.2026)
- P&H Engineering, Air admittance valves: getting it right (retrieved 22.10.2026)