Garden & Lawn

Top 5 Best automatic greenhouse vent openers for controlling the temperature and increasing airflow in your greenhouse

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This review of the Best greenhouse automatic vent openers for controlling the temperature in your greenhouse introduces you to the best models of this product to help you avoid cheap products that simply underperform or break.

I describe the features of each greenhouse automatic window opener and its pros and cons. I end each section with my recommendation as to who and where the product is good for. The individual product sections are relatively short as there’s not much difference between the openers. My Buyer’s Guide rounds this out by examining the different features of greenhouse vent openers that do make a difference.

Fitting new greenhouse autovent for testing
Bayliss XL Auto Vent Opener being tested over last 12 months

My Best Pick, which I have been very impressed with, plus it was super easy to install is the Bayliss XL Auto Vent Opener. This is a mechanical heat-powered window opener. If you have either a wooden or an aluminium greenhouse like I do, this vent opener will operate comfortably there and will fit almost all greenhouses. This is probably the best choice for most greenhouses which is why I have this model fitted to my own greenhouses.

My Runner-up for Best greenhouse automatic window opener had to be the Palram Greenhouse Automatic Vent Opener which I had installed previously on another greenhouse. This is also a mechanical vent opener almost identical to the Bayliss XL, however, it’s specially made for Palram greenhouses (which are very popular in the UK), many people including myself have this brand of greenhouse already so this is obviously a good model to start with for those people. As it happens, I have a Palmram greenhouse but have the Bayliss XL fitted to mine as I prefer it, I would say it’s slightly better.

BEST PICK

the Bayliss XL Auto Vent Opener which I think is the best automatic greenhouse vent you can buy
Bayliss XL Auto Vent Opener
The Bayliss XL Auto Vent Opener is a solar-powered piston vent opener that is suitable for smaller and medium-sized greenhouses. I like that it fits onto wood or aluminium greenhouse frames though you may have some trouble installing it in older greenhouses but its usually still possible. In addition, the XL vent opener handles a payload of up to 5.5kg so your vent window must weigh that or less (That covers most). The two-year warranty is generous altough I never had one stop working yet. I also like that if something does go wrong after this period, you can buy replacement power tubes individually should you need them, and not have to replace the whole unit.

RUNNER UP

Palram Greenhouse Automatic Vent Opener
If you have a Palram greenhouse, the Palram Greenhouse Automatic Vent Opener fits as it's designed to fit in the groves of the frame. This vent opener has a mechanical piston system that uses the temperature to open and close the vent like my best pick. The window starts opening at a temperature of your choice from 12°C to 15°C. If you like Palram products but have a different brand of greenhouse, check this one out anyway – it may be suitable but if in doubt I recommend choosing the Bayliss XL. This automatic vent opener could be a winner if you own, or are buying, one of the popular Palram greenhouse.

Check out my greenhouse reviews that include some of the Palram greenhouses


Top 5 Best Greenhouse Automatic Vent Opener Reviews

1. Bayliss XL Auto Vent Opener

BEST PICK

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Bayliss XL Auto Vent Opener

The Bayliss XL Auto Vent Opener is a solar-powered vent opener that operates mechanically and I think this model is probably the best one I have ever fitted in terms of stability. Overall, it’s also of great quality and works perfectly too.

The reason for this is most greenhouses do not use glass anymore and instead, use polycarbonate as it’s safer and cheaper. The issue with this is most auto greenhouse vents use the weight of the window to help close the vent and keep it stable in windy weather. This means, that if you have a greenhouse with polycarbonate sheets and not glass, they are often too light and are not stable enough. Thats what I have noticed anyway.

Strong spring helps hold light weight windows closed

This Bayliss XL, however, has a very strong spring that helps pull the window closed, instead of relying on the weight of the window to close the vent as the strut closes as the temperature cools.

You can also get this upgraded Bayliss Mk7 which has Triple Springs which would be even better but it’s not as easy to install as there are no clamps and the closing mechanism can prove harder to calibrate. With this in mind, for me, the Bayliss XL would be the model I would recommend for most greenhouses.

This automatic vent opener is made from anodised aluminium which makes it resistant to corrosion. The heavy spring holds everything in place firmly. The opener is resistant to damage caused by high winds (which is super important) when the window opens and closes.

Bayliss XL automatic vent opener
The Bayliss XL automatic vent opener as it comes

What I really like is that the Bayliss XL automatic vent opener is suitable for greenhouses made from wood or aluminium which is what I have fitted this one to. It’s also very simple to install as you screw the opener directly into the wooden frame or clamp it onto the aluminium struts between the glass and frame without the need for any drilling. I actually didn’t even use the clamps, these are the two plates shown above. I just screwed the vent directly to the greenhouse window and frame using the screws that were already there from the previous manual vent I removed before installing the auto vents. This was even easier.

However, depending on the model of your greenhouse, you may have to make minor adjustments to the unit like I did but for most people, this won’t be something you will not need to do.

Screws that already came with greenhouse frame that I wanted to use but were slightly to large so I drilled some new holes in the new vent
The two screws from the manual opener I removed. I used these to attach the new auto vent straight to the frame.

Basically, I removed my old manual vent opener and wanted to use the same screws from that as they were already attached to the aluminium frame to attach the new automatic vent opener as shown above. However, the holes were not quite in the right place so I had to put a drill through the bracket as shown below.

As you can see below, the vent opener was now simply inserted over the screws and was fixed in position.

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Anyway, this vent opener is suitable for opening hinged windows up to 60cm by 60cm (2ft x 2ft). That’s the standard size of many greenhouse windows. The window needs to weigh less than 5.5kg (which is usually the case) and its maximum opening with this vent opener is 30cm which I think is plenty.

You simply turn the dial to make mini adjustments so it opens perfected as soon as the greenhouse starts to heat up.

You can adjust the temperatures at which the opener opens and closes by simply turning a knob as shown above but this is best done when the window is closed.

One thing I forget to mention, before installing it, put the vent opener in the fridge for 30 minutes so it’s in the closed position and then install it.

Finally, the vent opener comes with a full two-year manufacturer’s warranty for all parts. If the power tube (with the oil inside) breaks after this period, you can order replacement tubes from Bayliss; you don’t have to replace the whole unit which is something you cannot do with most other models.

Pros

  • Solar-powered greenhouse vent opener so you don’t need an electric hook-up.
  • Screws into wood and clamps onto aluminium greenhouses without the need for drilling.
  • Anodised aluminium construction for durability and corrosion resistance.
  • Spring controlled so avoids damage from high winds. 
  • Suitable for opening hinged windows/vents up to 60cm by 60cm – a standard size in many greenhouses.
  • Adjustable temperature controls by turning a knob to handle changes in the weather.
  • Budget model so you don’t need to invest more money than your greenhouse cost into it.
  • Manufacturer-backed full two-year guarantee for all parts.

Cons

  • Not suitable for side vents.
  • Instructions are a little inadequate.
  • Installation problems with older greenhouses.

Our recommendation

The Bayliss XL Auto Vent Opener is a mechanical piston model that’s powered by solar power and I have found it to be very reliable. I’ve made the Bayliss XL Auto Vent Opener my Best Pick of greenhouse automatic vent openers.

If you have a small to medium-sized greenhouse and are looking for a quality automatic vent opener at an affordable price, this could be the one for you. If you have a polycarbonate greenhouse and the vents are VERY lightweight or more importantly, you have your greenhouse exposed to high winds, I would maybe consider upgrading to the Bayliss Mk7 Triple Spring variant. For most greenhouses though, this model would be a good choice.


2. Palram Greenhouse Automatic Vent Opener

RUNNER UP

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Palram Greenhouse Automatic Vent Opener

The Palram Greenhouse Automatic Vent Opener is another piston vent opener that is powered by the sun. It’s specially designed for the Palram line of greenhouses (except for discontinued models). If you have this brand of greenhouse, you know that this vent opener will fit. If you have another greenhouse brand, it may fit that as well.

The temperature at which the vent window opens is adjustable to suit different seasonal days. Choose a starting point for opening in the range of 12°C to 15°C. Installation of this automatic vent opener isn’t too bad, though some users say that the fixing screws are difficult to install and they’re in tight places that are tricky to get to. 

Pros

  • Mechanical piston system with solar power so you don’t need your greenhouse by an electric outlet.
  • Start opening point is 12°C to 15°C for varied weather conditions.
  • Fits any Palram greenhouses except for discontinued models.

Cons

  • Fixing screws are difficult to install.

Our recommendation

The Palram Greenhouse Accessory Automatic Vent Opener is specially designed to fit in Palram’s current line of greenhouses. If your Palram greenhouse is somewhat old, check the manufacturer’s website to see if it’s been discontinued. If you have another brand of greenhouse, this automatic vent opener may work with that as well.

This Palram Greenhouse Accessory Automatic Vent Opener is a good choice for you if you already own a Palram greenhouse which many people probably do because they are very popular.


3. Bayliss Mk 7 Window Autovent

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Bayliss Mk 7 Window Autovent

The Bayliss Mk7 Window Autovent is the standard model in a line of Mk7 autovents. It’s similar to my Best Pick, the Bayliss XL Auto Vent Opener, but handles slightly heavier vent windows.

It’s also more suitable than my best pick for very light polycarbonate greenhouses because the vents are lightweight or if you have your greenhouse exposed to high winds.

Mechanical solar-powered pistons power the Bayliss Mk7 Window Auto vent. This automatic vent opener comes in a satin anodised finish for resistance to rust and corrosion. 

You can install this vent opener in aluminium or wooden greenhouses, just like my best pick, so it works with whatever style of greenhouse you have.

However, some people may find installation can be difficult because you need small fingers to get into the small spaces to put screws in. Depending on the type and age of your greenhouse, you may need to custom install the Bayliss Mk7, maybe drilling new holes or using longer screws.

Opening and closing vent windows of up to 60cm by 60cm are no problem for this auto vent – as long as they weigh 6kg or less. The vent window opens to a maximum of 30cm to let an adequate volume of fresh air in. And you can set the vent window opening temperature anywhere from 12°C to 25°C. Spring, summer, autumn – this is a three-season vent opener.

The Bayliss Mk7 comes with a two-year manufacturer’s warranty. If you do need to replace part of the unit, Bayliss sells the parts individually. You don’t have to spend your money on a complete extra unit to get spare parts.

Pros

  • Opens greenhouse roof windows that are 60cm x 60cm. 
  • The payload is up to 6kg for heavier windows.
  • The mechanical piston works on solar power so great for a sunny summer day.
  • Opens the window to a maximum gap of 30cm for adequate ventilation for many plants.
  • Installs into wooden or aluminium greenhouses.
  • The adjustable opening temperature of between 12°C and 25°C lets you ventilate your greenhouse throughout the growing seasons.
  • Two-year warranty against faulty manufacture.

Cons

  • Difficult to install.
  • May need to custom fit the vent opener.

Our recommendation

The Bayliss Mk7 Window Autovent (standard model) is similar to my Best Pick, the Bayliss XL Auto Vent Opener. It has many of the same characteristics but can open and close a heavier window and as mentioned, is better for greenhouses with polycarbonate windows as it closes easier without the weight of the usual window glass. You have the ability to choose the temperature at which to open the ventilation – from 12°C to 25°C. This covers the needs of a wide range of plants at different stages of their growth.

If you have a greenhouse with heavy windows, perhaps glazed with toughened safety glass, the Bayliss Mk 7 Window Autovent may suit your needs.

4. Grow It Gardman Greenhouse Auto Vent

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Grow It Gardman Greenhouse Auto Vent

The Grow It Gardman Greenhouse Auto Vent is yet another mechanical vent opener with a piston that uses solar power to move. Most aluminium or polycarbonate greenhouses benefit from the ventilation provided by this vent opener. However, it may not fit older greenhouses that have a different structure to current ones.

This Grow It greenhouse auto vent has a long-lasting metal construction that’s both rot and rust-proof. The unit comes in a green finish that looks smart and is a change from the usual silver colour. The opening temperature is adjustable so you can change it with the seasons. This auto vent suits greenhouses with dimensions of 182cm by 182cm or larger. The air from the ventilation reaches all your many plants.

Pros

  • Durable metal construction that stands up against rot and rust.
  • Mechanical piston powered by solar energy so there are no wires to worry about.
  • Works with most polycarbonate and aluminium greenhouses.
  • The wax cylinders can be easily removed for winter storage.
  • Adjustable temperature for opening the vent to suit outside conditions.

Cons

  • May not fit older greenhouses.
  • Not for wooden frame greenhouses.

Our recommendation

The long-lasting metal construction of the Grow It Gardman Greenhouse Auto Vent keeps it safe from rot and rust. Its green finish adds style to your greenhouse alongside all your plants. If you have a greenhouse, that’s 182cm by 182cm or larger, this auto vent will keep it well ventilated. Remember to store the easily removed wax tube over the winter so as to not harm the contents with low temperatures.

If you have an aluminium or polycarbonate greenhouse that’s fairly large, take a look at the Grow It Gardman Greenhouse Auto Vent.



5. Gardening-Naturally Automatic Greenhouse Window Opener

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Gardening-Naturally Automatic Greenhouse Window Opener

The Gardening-Naturally Automatic Greenhouse Window Opener is made from aluminium-coated zinc steel. These materials give the vent opener sturdiness and durability. 

This Gardening-Naturally automatic vent opener handles larger and heavier window vents than the other products in this review. It has an opening force (window weight) of 7kg and opens to a maximum of 45cm. This maximum opening is reached when the temperature of the greenhouse is around 30°C. You don’t have to worry about your plants being fried on really hot days. 

The range of opening temperatures is from 17°C to 25°C. The specific temperature at which the vent opens depends on how you set up the auto vent. Installation of this model is quite easy, though some users report that the instructions are not easy to follow. However, YouTube videos are available if you need help so at least you have something to refer to.

Pros

  • Piston vent opener that runs on solar power so you don’t need an additional power source such as a battery.
  • Aluminium zinc-coated steel construction makes this vent opener durable.
  • The opening temperate range is from 17°C to 25°C; you set up what you want it to be. 
  • The window opens to a maximum of 45cm depending on how you adjust the unit.
  • Opening force (payload) is 7kg to operate heavier windows.
  • The warranty is for two years.

Cons

  • Instructions are not clear.

Our recommendation

The Gardening-Naturally Automatic Greenhouse Window Opener is constructed from aluminium-coated steel for years of opening and closing greenhouse vents and windows. The wide range of opening temperatures offers ventilation on cooler days as well as warmer ones. This window opener’s payload (weight of the window it can raise) is more than the other models in my review. It also opens a gap of up to 45cm, again wider than my other products here.

If you have a larger greenhouse with fairly heavy windows, consider the Gardening-Naturally Automatic Greenhouse Window Opener.


Buyer’s Guide

Good greenhouse ventilation is important to keep your plants from getting too hot, in every kind of weather. You can always keep track of the temperature yourself and run in and out to open the window vents as your plants need. But are you going to remember to do that throughout all of spring, summer and autumn?

Greenhouse automatic vent openers (sometimes called auto vents) take all the worry out of giving your plants the correct ventilation and keeping them at an optimum temperature. Automatic vent openers open the vent/window at a particular temperature and close it when the weather cools off.

The individual reviews in this article show that auto vents are similar to each other. The small differences may not be immediately obvious. This Buyer’s Guide points out the features to look for in an automatic window opener so you choose the best model for your greenhouse.

How an automatic vent window opener works

How an automatic vent window opener works

Window openers can be mechanical and solar-powered or electric. All the vent openers in this article are mechanical ones and we’ll focus on that. However, unlike mechanical openers, electric ones need a power source to power the strong electric mower that opens the windows. Electric vent openers also need an external temperature gauge to tell when the temperature reaches the pre-set limit or when it changes. These types of vent openers are usually installed in large commercial greenhouses.

In contrast, the way in which mechanical automatic openers operates is quite basic but ingenious. They work from a metal cylinder that contains mineral oil which expands when it’s hot. The expanding wax pushes a piston to open the auto vent and this then opens the window. As the temperature drops in the greenhouse and the wax cools, the spring contracts, the window is closed and the piston is reset.

These mechanical vent openers don’t need a power source or an external temperature sensor. The sun heats up or cools the wax and the opener does its job. You usually adjust the temperature at which the window is opened by turning the adjustment knob on the end of the unit.

Construction

Automatic vent openers are usually made out of metal. This gives them strength and resilience. The units that are powder-coated, coated with aluminium or anodised are also rust-resistant. Check that all the fastenings and fittings have a galvanised coating so you can safely leave the vent opener out in the winter. The galvanised metal also protects them from rusting from any humidity in the greenhouse. 

Look also at the oil cylinder, the piston, and the spring. They should operate smoothly together with no snags or scratches. The cylinder wears out over time and loses its temperature sensitivity. You need to replace the cylinder when this happens. Some manufacturers sell the cylinder by itself; others require you to buy another unit. If you’re on a budget, or just don’t want to spend more than you need to, look for automatic window openers with replaceable cylinders that are ideal and much more environmentally friendly.

Lifting capacity and window size

Choosing the right greenhouse window opener for your size vents

Lifting capacity (aka load capacity) and the size of the window that can be opened and closed are related. Generally, the larger the window, the heavier it is. However, your large windows may be lightweight if the glazing is of polycarbonate or other plastics. To be sure that you’re buying an automatic vent opener that can open your vent, measure the window for its dimensions and find out how much it weighs. (At the manufacturer’s website or in a review somewhere.)

Many of the vent openers in this review state that they handle windows up to 60cm by 60cm that’s the standard size for most greenhouses. The openers in this review can move vents with a weight ranging from 5.5kg to 7kg. If you have very large or very heavy greenhouse windows vents, look for an opener that handles weights above 7kg.

Temperature range

Tempature controlled greenhouse vent opener

The whole point of automatic vent openers is to keep your plants at the best temperature for them. Most openers have a temperature range from which you choose the opening temperature. When the greenhouse reaches that temperature, the window opens. The maximum opening of the window is usually upwards from a set temperate. For example, the opening temperature range may be from 15°C to 25°C and the maximum opening of the window may be at 30°C. 

Some vent openers have a wider range for opening and a higher maximum for full extension. Be sure to buy a vent opener with a range of opening temperatures that suit your climate and the plants that you grow.


Final Conclusion

You do enough already to care for your plants and to give them the best possible growing conditions. Reduce some of that load with a greenhouse automatic vent opener. This type of vent opener opens and closes your vent for you according to the temperature. The vent openers in this review are all mechanical ones that are solar powered in that they react to the sun’s heat. There are no wires to hook up and no batteries to keep charged. Different models can manage various sizes and weights of window vents. Be sure to find out what conditions your new automatic window opener needs to operate in.

My Best Pick is the Bayliss XL Auto Vent Opener. This is the cheapest of the models in this review but delivers most of the same features as the other openers.

The Palram Greenhouse Accessory Automatic Vent Opener is my Runner-up. This is designed to work with Palram greenhouses. 

If you’re interested in buying a new greenhouse, or more accessories, to go along with your automatic greenhouse vent opener, check out our other relevant reviews.

The Best Greenhouses

Top Greenhouse Heaters

The best small greenhouses


Last update on 2022-03-17 / Affiliate links / Images from Amazon Product Advertising API

Welcome to my site, my name is John and I have been lucky enough to work in horticultural nurseries for over 15 years in the UK. As the founder and editor as well as researcher, I have a City & Guilds Horticultural Qualifications which I proudly display on our About us page. I now work full time on this website where I review the very best gardening products and tools and write reliable gardening guides. Behind this site is an actual real person who has worked and has experience with the types of products we review as well as years of knowledge on the topics we cover from actual experience. You can reach out to me at john@pyracantha.co.uk

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