Conservatory cooling part II

Further investigations into the effectiveness of conservatory cooling techniques

Conservatory Cooling - What works?

In my previous article on conservatory cooling I described how in attempts to cool my 3.5x3.5m area south facing conservatory I had considered a solar coating, tried blinds, a ceiling fan and also used a pedestal fan but nothing worked. I had also previously purchased a rather noisy 12000 btu air conditioning unit which went back as the conservatory is mainly used as a treatment room for my wife's back pain clinic.

Quieter portable air conditioning unit

Despite my previous claims that I would call several air conditioning companies and ask advice on which would be the quietest I fell back to my scientist roots. This involved finding and reading the technical datasheets for several popular portable air conditioning units to see how many dBA they were quoted. My previous 12000 btu unit produced noise up in the 55-65dBA level. The dBA is the measure of noise adjusted to the frequency sensitivity of the human ear. Roughly a 10dBA increase is perceived as a doubling of loudness. The unit I chose was a 12000 btu Amcor air conditioning unit from Ebuyer. It had a quoted noise level of 49dBA and so should be at roughly half the loudness of the previous unit I bought. The unit cost £280 including VAT and delivery.


Air conditioning units produce heat in cooling the air they blow into the room. The warm air they extract and the extra heat they produce has to be vented out of the room via a pipe or permanent ducting. For a portable air conditioning unit it is usually via a flexible ribbed pipe that is either stuck out of the window or through a door that is slightly ajar. The key is to vent the hot air without letting the warm air outside back in. The flexible pipe is anywhere between 1.5 and 3m in length. The instruction warn that you must not try and extend this pipe or have to many extreme bends in it as the air conditioning unit may over heat. Why? Well, in order for the unit to expel the hot air down the pipe it has to provide a certain amount of pressure. The amount of pressure required depends on how fast the air is needed to travel, the diameter of the pipe and its length. If air cannot be expelled quickly enough then the air con units motor will get hot. The issue with this method of hot air extraction in a conservatory is that they don't usually have 'normal' windows. The windows that open in our (and indeed most) conservatory are at the tops of the window pane a good 1.5-2m above floor level. Problem! The connection point for the pipe into the air con unit is maybe 30cm above ground and so the pipe only just stretched to the window opening. I 'solved' the problem by using the expanded polystyrene packaging as a stand for the unit to sit on. Still the pipe isn't ideally situated as it has a 90 degree bend in it and had to push the hot air up the pipe to get out of the window. To help seal off the room from hot air getting back in through the open windows the unit came with a cover plate that fits around the exit of the hot air venting pipe and should fit in the gap made by the open window. In practise this doesn't work for our windows.

Cooling effectiveness

Firstly in the absence of any cooling our conservatory gets extremely hot. Prior to writing this article I have measured the inside temperature at 41C when the blinds have been down all day. That's as hot as India in summer! This is in a cloudless day at 3pm with an outside temperature of about 25C in the shade. The unit can attempt to maintain an air temperature between 18 and 23C. Whether it can do that depends on how much heat it can expel compared to how much heat is being generated inside the room. After running the unit for about half an hour I measured the air temperature at about 31C or 10C cooler, but still hot. This is for a unit that is rated at 12000 btu and so should be adequate for the size and location of the conservatory we have.

Air conditioner noise level

It certainly is quieter than the previous unit we had, even when it is in turbo mode, that is with the compressor running (actually air conditioning) and the fan on at full speed. I wouldn't say it was quiet, you couldn't easily watch TV whilst this thing was on in the room, but it isn't too obtrusive. My wife thinks it will be OK for noise level when treating the clients. Actually positioning it on the packaging helped reduce some of the noise due to vibrations.

Can it be improved?

I think both the noise level and the cooling ability would be improved by have the air vent at the same level as the exit hole in the air conditioning unit, rather than run up the flexible pipe and out of the window. This would also allow the pipe to be shortened in length and hence improve the rate of air expelling. To do this I would have to cut a large diameter hole the wall under the window similar to the vent for a tumble drier.

The other option is to buy a more powerful air conditioning unit. I did see some units that were quieter than 49dBA but had the price tag to match as £900. Typically a portable 15000 btu unit would also be louder than a portable 12000 btu unit. A split unit, where the compressor is outside the room, would be quieter per btu of cooling power but expensive. The actual units themselves aren't too bad. A 11000 btu unit can be found for £299 and is quoted at 41dBA for the inside part. The next size up on the site in question is a 18000 btu unit which should be powerful enough, the dBA has gone up to 46 and the price is £400. This price does not include installation costs. I'm not sure I would be confident in installing these units. Some of them require hard wiring into the mains and pressurising with the coolant gas before use. I think I would be looking at paying £500 for a fitted unit capable of cooling the conservatory and that's too much at the moment. Maybe next year.


We've spent quite a bit of money trying to cool our conservatory

  • Blinds - £1700
  • Ceiling fan - £50
  • Pedestal fan - £25
  • Portable air conditioning unit - £280
  • And managed to achieve a 10C reduction on a hot sunny day outside, but this temperature drop makes the difference between whether the room can be utilised as a clinic or not. If it had the chance to spend the money again I would have maybe bought and installed my own roller blinds on the vertical windows (rather than the more complicated shape of the roof) and used the money I saved to have a professionally installed split air conditioning unit (of maybe 18000 btu) fitted. The total cost would have been less than £1000 and saved a lot of time and resulted in a cooler room. If anyone has any other ideas and wants to try them on my conservatory (such as solar coatings) I would be happy to let you do so for free! ( as long as you are a professional company). The results positive or negative would be published in an article on this site.

    By Jonathan Pearson

    "You don't need any fans or air con for the conservatory just add a vent to let the air out, We have been making conservatory vent openers for years at it works by open the vent and closing it if it rains just look at"

    R j Wareham

    "Thanks Jonathan.. very informative. I was hoping your story would end with a happier and cooler ending. Looking forward to the sequel- Cooler Conservatories 3 - Result!"

    Living in an oven ! London

    "Hi we grew a plant on ours a wisteria on a frame. It works really well as the green leaves repelled the heat. It also cost very little . We have a 27 feet by 14 feet conservatory south east facing and we can use it all the time."


    "We came across a very simple and cheap way of keeping the heat off the glass of our conservatory roof when we were going away one year. I threw the kids camo net from their toy fort onto the roof. It instantly knocked 10-15degrees of the inside temperature. Now it goes on every summer and also gives a nice dappled light inside like sitting under a vine without the flies. £25 and I replace it every two years. Forget spending thousands - this works."


    "Ours is 10 m x 4 m with a full glass roof. The first time we walked into it we needed sunglasses! My husband is a window blind retailed but we decided against blinds as they can look dreadful after a few years, and even the trade price is absolutely exorbitant. Instead we use a combination of a portable air cooler (the sort you put water and ice in) which cost £50, and we have made lengths of fabric which hook onto the roof struts in summer and reduce glare while looking great. Once summer is over we take them down, roll them up and put them away until next year."


    "Very interesting and informative. I wish you had tried the solar film coating. Then I would have known whether to proceed or not. Regards Jackie owner of unbearably hot conservatory"

    J. Martindale

    "Having the same problem, I am trying to locate a silent fan and a controller that will switch it on at around 25 to 30 degree. The duct would take the heat and blow it into the house. Anyone tried this or have suggestions?"

    Robin Frame

    "Very good and comprehensive article. We have exactly the same problem and were hoping to integrate the conservatory into our lounge, ie, removing the patio doors to effectively make both areas into one room. However, the heat in the summer would make our new lounge uncomfortable so we have to find a cost-effective solution. The film seems to be the best bet - this CAN be applied on the inside of the roof, thus prolonging its life and keeping it away from inquisitive little fingers! We are going to take advice from the firm who built our conservatory first - maybe they will come up with the perfect solution for us. Watch this space!"

    Linda Gatiens

    "WE sell a vent open system that is very cheep to run and almost silent in operation this will remove all hot air from your conservatory and the vent will auto close when it rains. Contact my company EVW Ltd 01202 593104 for free advice on cooling"

    R J Wareham

    "excellent article, it really has helped us focus on our own conservatory problems."

    mrs f swanson

    "i also have a conservatory of a similar size to yours, up to now i have managed with a good floor standing oscillating fan and a 2metre cream garden umbrella on a roll about floor stand,this works for me as i spend realy hot days(we get a few) outside swinging on a garden hammock. There was a time though i did consider buying a very large camouflage net to throw over the roof of the conservatory as i feel the price of conservatory blinds is extortionate, as you say they are having a laugh. regards and thanks for a pleasant and informative read CAS"


    "I would have purchased a proper A\\C unit fro someone like B&Q. the price is reasonable. fixing requires that you put the condenser unit outside (part that transmits unwanted heat to the outside) and the evaporator unit on the inside it is really a plug and play unit only requiring the drilling of a hole for the tubes. comes with remote control and is really quiet and efficient"


    "Hi Mike I'm convinced your answer is the most sound. What is the manufacturers name of the automatic vent openers?"


    "A simple and very effective way to cool the air is to install a water feature (space permitting) quieter and more relaxing to listen to than an air conditioning unit."


    "Hi,we had tried all avenues with our conservatory even having extra roofing panels fitted inside the original ones. The new one were gold on the outside, which deflects the heat. It was cooler but no where near cool enough. So we resorted to the air con unit, it is an 1800 BTU and is wonderful and we did not have to have it professionally fitted it is quiet a simple DIY installation. The unit cost £450 Well worth the money."


    "We have a roof vent window which is connected to a temperature controller. Set the required temperature on the control box and the roof opens at that temperature. It also has an manual override switch and rain sensor (so shuts automatically if it rains). An air brick low down on the wall allows air in to circulate in and then out of the roof vent. Has worked well for over 10 years - currently sunny 24.4 deg. outside 29.4 inside conservatory with doors and windows closed and no blinds."

    Mike, South Wales

    "I use a 12000 BTU aircon to cool my computer room and it only cools it by 5 degrees C. The split units seem to work better than the portable variety. I am looking to build a 25 * 12 foot conservatory so will need to have professional advise on how to cool it."


    "Hi Jonathan I would be interested to know how the Conservatory Cooling saga is going. Did you consider using heat deflecting film for your conservatory roof? Unlike blinds that trap the heat between the glass and the blind, films like CoolKote (which we use at UV Shield-UK) deflect the solar heat away and make a significant difference to the internal temperature of your conservatory - you can compare the differences on or website"

    Sue Daniels, UV Shield

    "Sitting here in my conservatory now Glass roof, south facing, i can understand your posting. I have a 15000 BTU amcor, had to extend the pipe, no option as windows too high. The only way to stay cool is to sit with the cool air blowing on us directly. Even then, the machine is not able to cool the hot air it is intaking fast enough so the air coming out although cooler is not cold. Am also thinking of installing a professional unit"


    "I am considering building a south facing conservatory and my research recommends designing the base to act as thermal sink and store. A sufficient thickness of concrete of concrete base (~1m I guess) and black or very dark tiling as the absorber. I am told it is simple physics. The black tiles absorb the heat very efficiently and transfers it to the concrete base. The process reverses as the conservatory cools in the evening. The guy I was talking to say his south facing conservatory stays at about 25C even on the hottest days and its an effective heat source during the winter. The only problem I have is persuading the wife to have a black floor. Anyone have experience of this design ?"


    "Jonathon I was reading your article on conservatory cooling, I cannot determine whether you have a glass roof or polycarbonate, if you have the latter then solar inserts would be the answer."

    Richard, Polysert

    "What an excellent article, it answered some of our questions very well"

    J. Hooper

    "We have a south west facing conservatory, with gable roof. Current temp (4pm in the afternoon) is 31 degC, with all windows and doors open (outside temp is about 25), blinds down, but I have no roof blinds, but I do have tinted glass in the roof which supposedly cuts out 70% of the heat and glare (but seriously thinking about roof blinds now as can get up to 40 degC."


    "I use an extractor fan, much as one would use in a kitchen or bathroom. I used a core drill to go through the wall at the apex of the conservatory, and ran ducting up into the loft. There I installed an extractor box like this one: and connected it to a thermostat in the conservatory. This pulls the hot air out of the top of the conservatory and out through the eaves. The horizontal ducting was hidden behind box shaped skirting, and the vertical is in a cupboard. Overall a 10-15 degC lowering on temp."


    "Great article. I have exactly the same problem. My solution is to lay two layers of Gardman Brushwood Screening on the outside of the conservatory roof during the summer months. This permenantly puts the conservatory in the shade, and gives it a beach shack type appearance. I got the idea after a holiday in Thailand!"


    "Interesting article. We experience similar problems. Going to try totally different approach this year and hose down roof periodically - theory being to try and stop heat entering conservatory throught water vapour generated when roof heats up. Could be crackpot idea but we'd like to try out. Will let you know if any success (and if practical)!"


    "Re: White-wash and shutters. Don't think the whitewash would go down to well. The shutters are a good idea and have obviously been used for hundreds of years. I been wondering that same thing recently as well recently. Could look quite nice as well. Any one an idea on pricing? Solar inserts: I'm sure they do reduce the temperature in the conservatory but is it enough on a hot day? What about the windows rather than the roof? I don't want to have a laminate applied to my windows as it will get torn off and look shabby in a few months/weeks (kids eh!). However, I keep getting DIY install quotes from a company the sells it - £250 for my conservatory. How much would it cost for that to be installed, roughly? (3.5x3.5m ish). Thanks for the feedback."


    "Have you tried slatted blinds or dilute whitewash on the OUTSIDE of the glass? This is what they do on greenhouses. Stop the heat getting in, rather than removing it."


    "I have been installing solar inserts into polycarbonate roofs for about 4 years now and have always had a great response from customers. This is far cheaper than blinds and a lot more effective and is completely maintenance free. As well as all this it also shades the light so you dont get blinded by the sun and cuts down fabric fading. It also maintains any self generated heat in the winter.Feel free to ask any questions."

    The conservatory doctor

    "Hi, I have a conservatory of similar size but had split air conditioning unit installed as well. With installation I think it was around £1,800 but then given it heats(heat pump) the room as well and means I can use the room all year round I felt it was a luxury but just about justified. In the very height of summer it's still warm but not horrible and in those horrible hot evenings, I go and sleep in there with the air con on and it's pure luxury!"