• Bayliss MK7 Triple Spring Auto Vent Opener - 8040105
  • Bayliss MK7 Triple Spring Auto Vent Opener - 8040105
  • Bayliss MK7 Triple Spring Auto Vent Opener - 8040105
  • Bayliss MK7 Triple Spring Auto Vent Opener - 8040105
Retail: $74.95
Price: $64.95
Availability: In Stock - Usually ships in 1 to 2 days.




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These Bayliss MK7 openers have three heavy-duty springs which gives the opener superior closing power making it ideal for side wall vents and roof vents in windy areas. Opening temperature is adjustable (Ranges shown below). Maximum opening of 12" is reached at approximately 20° to 30°F above opening temperature. Bayliss MK7 vent openers are made from the best corrosion resistant materials: stainless steel, anodized aluminum, and brass. These are recommended for use with Cross Country greenhouse vents. Powertubes are interchangeable.

Bayliss MK7 vent openers are available with 2 different models. The only difference is the operational temperatures of the powertube. The Orchid Wax model allows you to keep the greenhouse warmer in cold weather while working well in hot weather also.

Bayliss MK7 Features

  • Adjustable temperature range:
    - Standard initial opening temperature range: 55° F to 70° F
    - Orchid Wax initial opening temperature range: 70° F to 85° F
  • Maximum opening of 12"
  • Recommended for vents up to 18 lbs.
  • Equipped with 3 heavy duty springs for windy locations
  • Made in the United Kingdom

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 spring closes the vent and resets the piston.

Product Manuals, Tips, Specs, & Guides

Bayliss MK7 Vent Opener Dimensions
Bayliss MK7 Vent Opener Installation Manual

Overall Customer Rating of 4 Reviews:

Opens Windows!

Installed on a Sunshine Gardenhouse. Needed to move the roof vent strut up an inch so this could screw into the flat rather than into the 1/4" width. Measure several times and predrill your holes.
You can remove the 2 outer springs to make installation easier as you check the motion. It feels a bit wobbly as you install, but the action is smooth.


needing a release

I like this autovent very much, it's well built and works well. The one limitation is that I've attached it to a cold frame, need to get into the cold frame to water, and sometimes have to open the top far enough that the piston comes out of the end. A quick release of some sort would be helpful.

Springdale, UT

Great Product!

Quick delivery, and easy to fit with clear instructions. Does exactly the job I need it to do: it works perfectly and has proved to be very stable in strong winds.


Bayliss Mark 7

These are the best vent openers we've used. Depending on your greenhouse design, replacement can be easy or a huge pain; plan your bench layout for access to the opener. A power tube might work for ten years or might fail much sooner; ALWAYS have a spare power tube or a spare complete opener on hand. We've replaced two power tubes on our first opener which we've been using for twelve years. Don't attempt to change the power tube without taking the opener off the greenhouse. Ask me how I know that.