Price: $65 - $70
Availability: In Stock - Usually ships in 1 to 2 days.

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 heat the greenhouse to higher temperatures for tropical plants in cold weather.

Bayliss MK7 Features

  • Adjustable temperature range:
    - Standard initial opening temperature range: 55° F to 70° F
        (Recommended for most applications)
    - Orchid Wax initial opening temperature range: 75° F to 90° F
        (Heating to high temperatures in winter)
  • 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

Item # 8040105, 8040106

Overall Customer Rating of 15 Reviews:
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Great Auto-vent openers!!!

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Well made! The holes did not align with the old ones so new ones had to be drilled to fit the new vent openers, but this is to be expected. The vents work great and if the quality is the same as the old ones that I replaced, then it will be another twenty years before I have to do it again!!! Very satisfied!!!

Southworth, WA

Expensive but worth it (Bayliss MK7 Triple Spring Auto Vent Opener)

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Our first opener worked so well, we purchased a 2nd one--our greenhouse has two wooden gable windows on each end and we needed some additional airflow. Both of them work well. We like that they were very easy to install and can be adjusted to open sooner or later (depending upon the temperature). Initially we were a bit concerned if our windows would be too heavy for the opener, but this hasn't been an issue.

Fayetteville, NC

Heavy Duty Auto Opener

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I purchased the heavy duty Bayliss Autovent MK7 with triple springs to replace a light duty Autovent in the roof of my greenhouse. The push rod became bent during a severe wind storm. The triple spring MK7 was a perfect fit 10-minute replacement. I highly recommend the Bayliss Autovent. Except for the one wind-damaged vent, mine have been trouble free for three years.


Works okay

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I have the orchid wax model. With the setting knob all the way in, it doesn't begin to open until the internal temp in the greenhouse reaches 85 degrees. Other than that it performs as advertised.

Works perfectly

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I placed this unit in my greenhouse on a side window to create better cross ventilation. I already have two of the same vent openers that operate the ridge vents on the greenhouse and they have been working flawlessly for the last years. I will admit to trying to save a buck and previously installing a "lesser brand" of opener on the side window. It did not make it a year before failing.
I went back to the tried and true and am happy I did so.
I very much recommend this vent opener.