Bayliss Autovents logo

01335 342981

Opening Hours

Monday- Thursday: 8:00-17:00
Friday: 7:00 – 13:00

Worldwide Delivery

Bayliss Autovents logo

01335 342981

Bayliss Autovents and Autovent Spares can be purchased online, worldwide.

Prices are shown without VAT, which will be added at checkout to UK and EU customers.


Lysander Works, Blenheim Road,
Airfield Industrial Estate, Ashbourne,
Derbyshire DE6 1HA United Kingdom

Phone: 01335 342981
Fax: 01335 343860



Although we try to include all the relevant information about our greenhouse autovents in our product catalogue and information pages, you may find the answers to any specific questions here.

If you are unable to find an answer to your query then please do not hesitate to contact us.


Q: What does the Bayliss Autovent do?

A: It opens and closes a hinged vent automatically using energy from the warmth of the sun or the surrounding air. The hotter it gets, the wider the autovent opens the vent. And because it uses no electricity etc, it is a very environmentally friendly product.

Q: What liquid is inside the tube?

A: It is a special blend of mineral wax.

Q: How do I tell what model autovent I have?

A: There are photos of all previous units in our Autovent Identification Guide, along with pictures of all the different tubes in the Product Catalogue.

Q: What is the autovent made of?

A: The very best corrosion resistant materials including stainless steel, brass and aluminium. Great care is taken to avoid electrolytic corrosion which can occur in the warm and wet conditions in which the autovents work.

Q: Why is the Bayliss Autovent better?

A: It has been designed by engineers who have been making automatic vent controls for nearly 50 years and incorporates all the knowledge and experience gained during this time.

All our autovents have a strong stainless steel spring to give a firm closing force, virtually eliminating any risk of wind damage. The unit gives a balanced lifting action in the middle of the vent and this avoids any sideways thrust on the vent which can twist it or even push it out of position. The autovents are designed in such a way as to fit close up to the window avoiding loss of headroom. We make each and every part of our autovent here in Derbyshire and are able to respond to specific requirements and also to design bespoke units for special applications.


Q: I’ve got a 10 x 8 greenhouse with four windows in it. How many autovents do I need?

A: No matter the size of the greenhouse you have, the idea is always to ventilate 20% of the floor area. Sometimes however, this is just not possible, so a vent opener on both sides of the greenhouse is a good idea. This creates a good air flow. Using a Triple Spring autovent on a side window that opens vertically creates an even better flow due to convection.

Q: Which autovent do I need for my greenhouse?

A: The things you need to think about when choosing which autovent you need are the weight of the window, the size of the window, whether it’s in a windy exposed position and whether it’s wood or aluminium. The products information page explains each autovent, but as a rough guide you will need an XL for lightweight aluminium vents in a sheltered position, a Mk 7 for general aluminium and wooden vents in a reasonably sheltered position, a Mk 7 triple spring for side vents and vents in windy areas, a Mk 7 hydraulicheck for vents in a very windy area and the Mk 7 Super for very heavy double glazed vents.

Q: I live in a very windy area. Can I still use autovents in my greenhouse?

A: Yes, you can. The triple spring autovent is fitted with three strong stainless steel springs which give a closing force, in addition to the weight of the window, of about 2 kgs. This means that the window is held much steadier in a wind. The Mk 7 with hydraulic check provides an even safer option. The addition of a small hydraulic damper only allows the vent to open slowly but can shut it quickly. It works like those struts on a car boot!

Q: Will the autovents be able to lift my very heavy double glazed windows?

A: The Mk 7 Super unit is guaranteed to lift a total vent weight of about 31 kgs, or a load of 15.5 kgs. It will lift even more than that, but would take longer to gather enough energy to start opening the window.

Q: What’s the difference between total vent weight and load weight? How do I measure it?

A: The total vent weight means the weight of the window if you took it off the greenhouse or conservatory and weighed it independently. The load weight is the weight of the window if you weighed it at the point where you are going to fit the autovent. Load weight usually works out about half of the total vent weight, as half the weight of the window when it opens is taken by the hinges. The best way to weigh it is to get a lath of wood, put it under the part of the window to which you are going to fix the autovent, and let the other end rest on a pair of scales. The weight shown on the scales will be the load weight i.e. the weight at point of attachment.

Q: My window measures 2 feet by 3 feet. Will the autovent work on a window that size?

A: The autovent you choose is really governed by the weight of the window it is going to open. If, however, the window has a large surface area, it is always a good idea to fit the triple spring version, as it will help to prevent wind getting under the glass and blowing the window back on itself. The larger the area of glass in the window the greater the risk of vent flutter.

Q: Can I put two autovent units on one window?

A: This has been done, although it’s not something we would necessarily recommend. If the autovents are fixed at either end of a long window, there could be a temperature fluctuation which means they would start to open at different times. The result of this would be vent warping. Units have to be set very carefully so that they work in tandem to prevent this happening.

Q: Can I use an autovent on a window with friction hinges or scissor joints?

A: Unfortunately not. These types of hinges are often used on UPVC windows on conservatories. Friction hinges are usually fitted at the side of the window which means that it drops down a little before it opens and there is not enough clearance for the unit to work properly – the autovent will foul the glass. Scissor windows move down when they open and our units cannot compensate for this movement. The autovent only works on windows fitted with normal butt hinges.

Q: Can I use an autovent on a window that’s only 9 inches deep?

A: There is a Mk 7 mini version available but it is a specially manufactured item. The trouble using such a small autovent is that the size of the tube and piston needs to be correspondingly short, so the opening distance is very limited. The mini only gives about 3 inches of opening. Contact us for details if you are interested.

Q: Can you tell me how I could distinguish if I have the standard piston or the orchid piston installed?

A: We always stamp the end plug of an orchid wax tube with an ‘O’. If there is a ‘H’ stamped on the plug, it means it is a tube made for a Hartley greenhouse.

Q: Do you have any pistons that open at higher temperatures than the orchid piston?

A: No. The orchid wax blend is the highest opening temperature we use in our tubes at the moment.

Q: Your website says the standard MK7 has a lifting force of 14 pounds (6Kg). Some dealers say 18 pounds. Can you clarify that? Am I correct that is lifting force not total vent weight?

A: The Mk 7 is guaranteed to lift a load weight of 14lbs (approx 6.5kgs). The autovent will lift more but will take longer to gather the energy to start opening the window and may not last as long as a tube lifting the maximum load weight. Lifting force/load weight is approximately half the total vent weight, as half the total vent weight is being taken by the hinge when the window is being opened by the autovent.

Q: I can't find the lifting force for the triple-spring model. I assume it is less because it must also counteract the force of the extra springs. What is it?

A: The Mk 7 Triple Spring lifts roughly the same as the Mk 7 Standard autovent.

Q: My greenhouse is in a very windy area. Will the autovents resist wind gusts of 110 mph?

A: In many cases the limiting factor is the ability of the building itself to withstand the wind forces. Our Mk 7 Hydraulicheck unit will cope with strong winds but we are unable to guarantee it will resist wind gusts of 110mph.

Q: Is there an autovent suitable for a double-glazed conservatory? We have them in our greenhouse and they are superb.

A: The autovent you need to install is always governed by the weight of the window it is going to lift and, to a certain extent, by its dimensions.

As a rule, if a window weighs 14 lbs (6.5kgs) or less at point of attachment, you should fit a Mk 7, or one of its varients, and if over 14lbs (6.5 kgs) at point of attachment you should fit a Mk 7 Super. Double glazed vents are usually quite heavy, so you need to weigh the window carefully before you make your decision.

Windows that are light but large should usually be fitted with a Mk 7 Triple Spring or Hydraulicheck unit, as large surface area windowscan be affected by vent flutter due to wind fetting underneath the glass.

Q: Is a Bayliss autovent suitable for use in areas where temperatures can fall below freezing point?

A: Yes. There is no evidence to suggest that low temperatures would damage the tube. We can experience temperatures as low as -15 degrees Celcuis (5 degrees Fahrenheit) here in the UK, and the autovent units on our own greenhouse have not experienced any problems.

Q: Can an autovent be fitted to a cold frame?

A: Yes, although you might need to fit a quick release catch of some sort to allow disconnection of the autovent from the frame so that it can be lifted for access.


Q: There is no fitting guide in the package, although I believe I have a basic install understanding, I'm concerned about correct installation and conditions. Is there a pdf online?

A: All autovents leave our factory accompanied by a fixing instruction leaflet. If for some reason your unit does not have a guide our instruction leaflets are available on our website for download.

Q: How do I fit my unit?

A: There are many different designs of greenhouse vents, and it is impossible to list them all! Choose the fitting method most suitable from those shown in the Fitting and Setting Instructions. Make sure the autovent is fitted as near as possible to the middle of the window so that it will not twist. To ensure that the autovent is not overloaded, and that head room or growing space is not reduced, IT IS MOST IMPORTANT THAT THE GAP BETWEEN THE STRAIGHT LINK AND THE GLASS IN THE VENT IS THE SAME AT BOTH ENDS WHEN THE WINDOW IS CLOSED.

Q: How can I adjust the opening temperature of my autovent?

A: Look at the fitting instructions for your autovent in the ‘How to Fit‘ section.

Q: How do I get the autovent to close more quickly when it rains?

A: Unfortunately, you can’t. Our autovents work on temperature and not moisture. If you have a conservatory with soft furnishings that you don’t want to get wet, then the only answer is to go down the electronic route.

Q: How can I fit my XL unit to a Hall’s greenhouse?

A: The configuration of the Halls Greenhouse cill bar and vent means that you need a special fitting kit, which you can find here.

Q: How can I fit my XL unit to a Robinson’s greenhouse?

A: The Robinson’s Greenhouse requires a special fitting kit, which you can find here.

Q: The fitting guide emphasises the importance of having the straight arm parallel to the window when closed. I have found this difficult to do with the roof vents in my greenhouse. Why is it important? Can you recommend the best way to fit for roof vents?

A: It is very important indeed that the Bayliss autovent be fitted parallel to the window. If the unit is not fitted like this, the forces excerted on the power tube when the window starts to open are much greater than they would be if fitted correctly, due to the fact the power tube is trying to push the window back against the hinge.

If you have difficulty achieving parallel fitting, you can always give us a call and we shall be happy to help you. Our number is 01335 342981.

Q: How can I reset my autovent?

A: Unscrew the adjuster and put it somewhere safe! Take the unit off the window, put the unit into the fridge for half an hour, then remove it and place the steel piston road against a hard surface and push it firmly back into the tube. A resistance will be felt. The amount of piston still showing on the Mk 7 should be about 3″/7.5 cms and on the XL about 2″/5 cms. Then follow the setting instructions on the Installation Guide.

Q: Why is one of my autovents opening fully, and the one on the other side of the greenhouse not opening as much?

A: Probably because of temperature fluctuation. Often, one window in the greenhouse will be on the sheltered side, and the other on the windward. The unit on the sheltered side will be open further and for longer than the unit on the windward side.

Q: If the MK7 with the standard cylinder is set to begin opening at 70 degrees, what will be the maximum opening distance?

A: If you set the Standard unit to start opening at 70oF (21oC), you are already using some of the tube’s available piston travel. This means that the maximum opening will be reduced to about 8″ (20cm).


Q: What maintenance should I do on the autovent?

A: The only maintenance needed on the autovent is a general wipe down from time to time, and a little oil applied to moving parts. It’s also a good idea to carefully wipe the piston rod a couple of times a year.

Q: Do I need to take the autovents off the window during the winter?

A: No, you shouldn’t have to remove the autovent in the winter. There is no evidence to suggest that very low temperatures damage the tube.


Q: Can I get some more liquid to put in my tube?

A: Unfortunately not. If the power tube has lost its liquid, which is a special blend of mineral wax, it generally means the seals etc have become worn. If you were to top the tube up, the seals would still be worn and would still allow the wax to leak out. This would mean there would not be enough pressure inside the tube to open the vent.

Q: My autovent doesn’t open the window anymore. Can I get it mended?

A: Yes, all our current autovents are serviceable. All you need to do is have a look at our Autovent Identification Guide, identify the one you need to service and let us know what you want. Our autovents are guaranteed for two years against faulty manufacture. We also make spares for the Mk III and Mk V units which were made during the 70s and 80s. Also, check that the unit is set properly. Details of how to do this can be found in the Installation Guides available on this website.

Q: Can I get a new adjuster? I’ve lost my old one.

A: Yes. Have a look on the spares page for information.

Q: My autovent won’t close the window anymore. What can I do?

A: This usually means that the tube isn’t functioning properly. Tubes are easily replaceable – have a look on the spares page for details. Also, check that the unit is set properly. Details of how to do this can be found in the Installation Guides available on this website.

Q: My XL unit falls off my greenhouse vent. What can I do to stop this happening?

A: The XL has been designed as a clamp on unit and the standard XL clamps are made from plastic. If the greenhouse is epoxy powder coated or painted, it sometimes means that the plastic clamps don’t have enough ‘bite’ to stay on the window. If you have a greenhouse like this, use metal clamps and you’ll find there won’t be a problem. Have a look at the spares page for details of the metal clamps, and contact us if you need them.

Q: I can see a viscous liquid leaking out of the tube. What is it?

A: Mineral wax. Over the years, the seals inside the tube become worn and gradually, the wax leaks out. This means that the pressure inside the tube is reduced and is therefore not great enough to open the window. It is now that you need to replace the tube. A tube should last about 6 – 8 years before it needs replacing. It depends on how many cycles it completes. Replacement tubes are available from our Product Catalogue.

Q: My autovent doesn’t seem to be opening. How can I see whether the tube is still working?

A: If you have a power point nearby, the easiest way to do this is to get a hair dryer and blow hot air over the tube. If the tube is still operating, the window will quickly start to open.

Q: Is it a good idea to keep a spare tube handy?

A: No, we don’t really recommend this. The wax inside the tubes expands and contracts with the heat whether they are installed on the unit or not, so it’s a much better idea to get them when you need them. Neither is it a good idea to buy one and keep it in the fridge, as over time, the seals may stick.

Q: Having recently replaced the Power Tubes on Mk 7 Autovents I wondered whether the old tubes are recyclable? Structurally they appear to be sound and I wondered if you could refurbish and recharge them rather than them being thrown out?

A: Unfortunately, the cost of refurbishing the tubes and replacing old and worn parts is too high to make recharging the tubes a viable proposition. We would ask therefore that should you need to replace a tube, please dispose of the old one at your local recycling centre or pop it in your own recycling bin.

Q: I have two Mark 7 Super auto vents on my green house. Is the Mk 7 Standard Power tube the correct replacement to buy?

A: No. You need to buy the Mk 7 Super Power Tube.


Q: I’m not based in the UK, can I buy direct from you for delivery to another country?

A: Yes you can, and in most cases you can buy online. Just add the products you need into your basket, complete your address and country details and the website will calculate the total price including carriage. You can complete your purchase online and your autovents will be shipped to you as soon as possible.

Q: I don’t like using online shopping, can I still buy from you?

A: Our payment processing system is secure, but if you prefer, please contact us by telephone and we can process your order that way.

Q: Can I get a discount if I buy a lot of units?

A: If you buy more than 6 units in one go, we can arrange a discount. Contact us for more details.

Q: Can I get my autovents in a different colour?

A: We can supply the Mk 7 range of units in silver, white, dark brown and green and you can select the colour you prefer when making your purchase. However, if you want a specific colour to match your greenhouse or conservatory, contact us and we will let you know about cost and lead time. The XL is only available in silver.