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



How does a Greenhouse Autovent work?

A strong metal tube contains a mineral wax which expands with heat. This pushes a piston which opens the auto vent via a balanced linkage. As the temperature drops, the wax shrinks and a strong stainless steel spring closes the vent and resets the piston.

The Autovents are operated by the expansion of a mineral wax. The high rates of expansion are concentrated over the phase change solid-liquid. The piston works directly in contact with the wax and the lowest temperature we have so far been able to utilise is about 55 degrees Fahrenheit. Other waxes and blends of wax can be used to give higher opening temperatures.

The viscosity of the wax causes a hysteresis giving a temperature difference of 5 degrees Fahrenheit to 10 degrees Fahrenheit, opening to closing, although this may be possibly reduced by careful blending of the wax.

Response time is somewhat governed by the load on the piston. The energy to move the load is collected from the surroundings and is governed by the surface area of the tube in which the wax is contained. For the smaller units we use a plain aluminium tube but for the larger we use a tube which is finned on both the outside and the inside bore. Wax is a poor conductor of heat.

Why are Bayliss Autovents better?

They have been designed by engineers who have been making automatic vent controls for 50 years, and incorporate all the knowledge and experience gained during this time. All Bayliss Autovents have a strong stainless steel spring to give a firm closing force, and this virtually eliminates any risk from 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 or push it out of position.

View the full range Bayliss Autovents in our Product Catalogue

Custom designed Autovents

The details given on this website show our standard range of automatic ventilation units. However, because we design, make the components and assemble them ‘in house’, we are able to offer special versions of the Bayliss Autovent. Variations can include alternative finishes and colours, different operating temperature ranges and even special designs for specific applications.

Contact us to discuss your requirements