• 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 7 Reviews:

Exactly what I needed

I constructed a cold frame, using an old glass door insert. Not sure how much it weighs? But this lifts it perfectly and shuts it back down when the temperature drops.

Bayliss MK7 Triple Spring Auto Vent Opener

The old one has functioned properly for several years. With a horrible wind it ruined the working parts. I wish I would have checked out the greenhouse further because I have partial issues on another and will need some parts for it.

Works great

The item was easy to install with the directions. Waited for a warm day at saw that it worked great. Was a little concern because of the weight of the vent because it is glass. But it had no problem what so ever to work. Just make sure to follow the instructions before use.

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.