What size air conditioner do I need?

Having air conditioning installed is a worthwhile investment, a significant expense, and a decision that requires careful planning.

You may already have done some research yourself, perhaps you’ve looked at how air conditioners work, and which size and types you favour. There may be some features that you consider are important, such as running costs, aesthetics, or smart technology.

However, bad choices can lead to disappointing results, and soaring energy bills, something we that all wish to avoid. In this article we explain why buying an air conditioner with the correct output, should be top of your list, and a crucial part of the selection process.

Does size matter?

Yes, we know it’s a cliché, but size matters. In fact, it is the most important consideration.

An air conditioner that’s too small will not heat or cool your room effectively, and one that’s oversized will be inefficient and expensive to run. It important that we first establish that size in terms of physical dimensions, and size in terms of output, are two separate entities.

From now on we want you to think of size as your unit’s ability to produce cool and/or warm air. In this industry we measure size in kW (kilowatts), and sometimes BTU (British Thermal Units).

Simply put, size is all about output, or in technical terms, the duty. The duty has a direct impact on how your AC system will perform in terms of efficiency and running costs.

Bigger is not necessarily better

A unit that is oversized for an area can put too much pressure on the system’s components. It will be costly to run, and costly to repair, if your system packs up.

Physical size doesn’t indicate the efficiency or power of a unit, technology advancement means that some of the smaller more compact designer air conditioners can offer much more than the older bulkier systems.

An oversized system will stop and start more often. This is not energy efficient and will lead to increased energy bills. Not only that, but you will also struggle to maintain an optimum temperature and will often find that the room is too hot or too cold.

The correct size ac unit will effortlessly keep your room at the optimum temperature.

Undersized unit = oversized bills

An undersized AC unit will need to run constantly, and will not be powerful enough to reach, and maintain, the optimum room temperature. This will mean higher energy bills. An undersized unit that is having to work too hard, can also hit your wallet hard in terms of maintenance costs, and could result in your unit having premature wear and tear, breakdowns and a shortened life span.

Other factors that will affect size …

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There are several variables to consider that will impact selection of the duty (kw or BTU) of an air conditioner:

How well insulated is the building?

Adequate insulation directly affects the efficiency of your air conditioner, if you do not have a well-insulated property this will need to be considered when calculating kw size. Poorly insulated homes or workplaces may require an AC system with a higher output.

Is the room south-facing?

South facing rooms are exposed to more sunlight and heat, which means that you will have more heat gain. Your AC system will need to work harder to keep south facing rooms cool and you would need to make additional allowances in your calculations for this.

How much of the external walls are made of glass?

The size and orientation of the windows is especially important. South facing windows result in high solar gain which will be taken into consideration when calculating KW/ BTU size. You may need a more powerful unit.

Where is the room located?

Warm air rises, so an air conditioner in a loft space will need more cooling capacity than a ground floor room.

Is there electrical equipment within room?

Rooms such as comms rooms or entertainment rooms contain heat generating electrical equipment, and this increased need for cooling will need to be catered for when choosing the size of your air con unit or units.

Is the room an above average height?

A room with a high ceiling has much more volume than a room with a standard ceiling height and a larger unit may be considered more suitable here.

How to calculate the correct size …

Use our simple calculator to estimate the correct size air conditioner for your room

    [calculate_button "Calculate AC Size in KW"]

    This calculator uses the simple formula of 125 watts of cooling per square metre to estimate the best size for your space, however it is important to remember that there are other variables (such as those above) that will need to be factored in.

    Always round up to the nearest 0.5kw

    This is for estimation purposes only; a qualified engineer will be able to tell you the exact size for your individual requirements.

    Here is an example of how to estimate AC size for a room …..

    A room that meets standard criteria of 5 metres in width 7 metres in length which gives me a total area size of 35m2. Based on 125 watts per square metre I would need a minimum of 4.375kw of cooling.

    Simply …
    5 x 7 = 35 x 125 = 4,375 (watts)

    Air conditioning unit size required = 4.5kw or around 15,300 BTU. Click below to see BTU to KW conversion chart.

    BTU to KW Conversion chart
    BTU KW

    How much does air conditioning cost?

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    Commercial installations

    Each commercial air con installation will present with entirely different heating and cooling requirements.

    To meet these diverse applications there are a range of air conditioners available with different set ups and layouts, from single split systems to complex VRF or VRV systems.

    As one size does not fit all, it would be difficult for you to estimate the cost of your installation. Therefore, it is essential that you enlist the expertise of an experienced and accredited AC installer, who will confidently identify your needs and design a tailor-made air con system to fit your individual circumstances perfectly.

    Domestic installations

    Firstly, use our size calculator to estimate the size unit you will require. Then refer to the table below to get an idea of your air conditioning cost of installation.

    Remember when considering size, it is important to consider the different variables listed above.

    This table is for estimation purposes only, the final price of your install will be dependent on which manufacturer you choose the pipe run (distance from indoor to outdoor) and which type of unit you opt for (e.g. wall mounted, ducted).

    £1200 - £1600
    £1300 - £1700
    £1400 - £1800
    £1500 - £1900
    £1600 - £2000
    £1700 - £2100
    £1800 - £2200
    £1600 - £2000
    £1700 - £2100
    £1800 - £2200

    If you would like any further advise on which size and type of AC system is perfect for you, please contact our specialist team at Evergreen Air Conditioning Limited. We offer a free survey carried out by an experienced engineer followed by a free, comprehensive, no obligation quotation.

    Why Does My Air Conditioning Smell Bad?
    8 Reasons and Fixes

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    If you notice an unpleasant smell coming from your air conditioning unit, your ductwork, or your surroundings are not smelling as fresh as they should, it could be a sign that your air con system needs attention.

    We have consulted with a qualified service and maintenance technician, as to what are the most likely causes.  Drawing from his many years of experience in the industry, in this article we discuss eight of the most common aircon smells that are reported, and how best to tackle them.

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    1. Burning/Electrical Smells


    Your air conditioner contains many electrical components, and a malfunction of one of these could present a fire risk.

    If you smell burning, this could be down to an ELECTRICAL FAULT. Switch off your unit and contact your AC professional URGENTLY.

    Never attempt to solve a burning issue yourself, you will be putting yourself at risk of serious injury. This problem is one for the experts only.

    Not all burning smells are hazardous, a slight burning smell could be a result of dust burn off if you have not used your aircon for some time. However, we would still recommend that you SWITCH OFF AND SEEK ADVICE before assuming that this is the case.

    BE PROACTIVE. There are steps that you can take to prevent air conditioning fires and being proactive is the best way to protect yourself, your loved ones, or colleagues.

    Never obstruct your air conditioner. Never store flammable materials nearby. A thorough, comprehensive, and regular service by a specialist engineer will ensure that your equipment is clear of debris, functioning properly, and any early signs of wear and tear will be picked up, and dealt with, before they cause a serious issue.

    2. Damp, mildew or mouldy smells


    What causes the damp, musty, wet socks or rotten wood smells coming from your air conditioner?

    The build of up of human and pet dead skin cells and hair may sound harmless enough, however these particles provide a perfect breeding ground for any bacteria, mildew and mould in your AC unit.

    Contained within your air conditioning unit is a filter. Its main function is to prevent dust, hair, dirt and other particles from reaching the components in your system. If your filter becomes clogged by the build-up of these unwanted particles, then the bacteria and mould that thrive in this environment will quickly multiply.

    This bacteria and mould release an unpleasant odour, that your air conditioner will then circulate around your room. The spores from the mould, and bacteria, can also be circulated, potentially putting your health at risk.

    The filter in your aircon unit also helps to reduce the presence of dust mites, allergens, and pollutants, which can cause asthma attacks or respiratory illnesses, another reason why regular cleaning is very important.

    A service by a professional will keep your home, or working environment, free of unpleasant smells, and will help to make it a healthier place to be too.

    For domestic installations it is advised that your air con is thoroughly cleaned and inspected by a specialist once a year. For commercial installations, twice a year is recommended. This process involves stripping back the filter, fan scrolls, coils and cases and cleaning with specially formulated products.

    3. Rotten Eggs (refrigerant leaks and dead animals)


    Concerned that the rotten egg/sulphur smell coming from you aircon could be a refrigerant leak or a dead animal?

    Refrigerant Leaks

    AC systems manufactured prior to 2010 contained R22 (Freon) refrigerant, which if leaked, gave off a sulphur smell. So, if your unit is an older model, and you can smell rotten eggs, we would advise you contact your AC specialist immediately.

    R22 has now been banned because of its negative impact on the environment. AC units manufactured since 2010 use R410A, and more recently, R32 refrigerants, both are virtually odourless.

    This means that a smell of rotten eggs is unlikely to be the smell of leaking refrigerant coming from your air conditioner itself. We would advise you to investigate your surroundings, as any smells near to your air conditioner, are likely to be recirculating.

    A rotten egg, gas or sewage smell could be a sign of a problem with your drains or plumbing, or could be an indication of a faulty gas appliance, in both instances we advise you seek professional advise immediately.

    Finally, if you are still concerned that you have a refrigerant leak, get in contact with your AC specialist as soon as possible.

    Dead animals

    In ducted AC systems used in larger domestic and commercial installations, it is possible for a small animal, such as a bird or mouse, to enter your AC system via the ducts, and then perish. The decomposing remains will give off a pungent smell, which will then be circulated around your air space.

    These animals could also be carriers of bacteria and viruses, which could pose a threat to health, another reason why this issue needs to be acted upon promptly.

    Locating and removing the decaying carcass is a challenge that is best addressed by a professional. Once the animal has been safely disposed of, specialist products will be used to completely clean and sanitise the area.

    4. Chemical aromas

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    Remember that an air conditioning system is designed to circulate air around your room. If you air con unit is situated alongside an area where there are odours, then these will also be circulated. Cooking smells usually tend to dissipate quickly but chemical smells including scented cleaners or bleach, and cigarette smoke, can get trapped in the unit, and will be obvious in the air for much longer.

    In larger commercial buildings this will be less of a problem as ventilation systems are frequently installed enabling fresh air to be supplied, and stale air to be extracted, along with any odours.

    The careful planning of the position of your unit is important, and your AC specialist will advise you on which type, and position is best suited to your needs.

    5. Vinegar

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    As we have discussed before, an air conditioner that is in need of a service or has been left unused for a long period of time (perhaps over the winter), could be harbouring some rather repulsive odour releasing bacteria and mould.

    In this warm, moist environment these offensive micro-organisms will happily thrive and can omit an acrid odour that many people describe as a vinegar smell.

    A vinegar stench should be investigated as soon as possible, as it could be an indication that harmful spores are present and are being circulated around your living or working area, putting your health at risk.

    It is advisable to call in a professional to pinpoint the exact cause of the offending smell and decide on the best method to eradicate it. In a domestic situation the bacteria and mould could be located within the unit itself and in larger installations or commercial settings this could within the ductwork. Excess moisture or a clogged filter could also be the culprit.

    A regular deep clean and thorough check over by a qualified AC engineer, will keep your system operating as it should, and help ensure that the air you breathe is not harmful to your wellbeing.

    6. Fishy smells

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    As with burning and electrical smells the smell of fish coming from your air con is potentially a fire hazard and a situation that requires URGENT ATTENTION.

    Before reading on we would recommend you immediately SWITCH OFF your air conditioner and SEEK ADVICE from an AC professional.

    It is a common misconception that these fish odours could be down to bacteria and mould, or perhaps a decaying animal, but in fact the most common cause is due to OVERHEATING OR MELTING PLASTIC. When a component becomes faulty the plastic within can become extremely hot. The melting or burning plastic will emit a fish smell that will be circulated around you living area or workspace.

    This said, your AC system contains a circuit breaker, which is a safety switch that protects your equipment from damage by turning off the power when an overload or malfunction is detected. It also protects your safety since overloaded circuits can result in a fire. This means that your system should automatically switch off should there be a fire risk, however we would still advise that if you can smell fish or burning, you immediately switch off your air con as a precaution, it is better to be safe than sorry. It may be that the odour is being circulated from elsewhere in the room/building, potentially a faulty electrical appliance elsewhere, and this will need investigating further.

    If you detect fishy, electrical or burning smells coming from your air con system, do not attempt to identify the cause of the problem yourself, you will be putting yourself at risk of serious injury. This problem is one for the experts only.

    The regular servicing of your AC system will ensure that your air con is functioning properly. An experienced engineer will be able to detect any early signs of a faulty component and will be able to repair or replace it before it becomes a serious hazard.

    7. Stinky feet


    A distinctive smell that may have had you looking around accusingly at your family members or work colleagues!

    However, the odour of sweaty or smelly feet could be coming from your AC system itself, and could be a sign of a grimy, clogged up air con, dirty coils or even a blocked condensate drain, there are many possibilities. This offensive stench will be circulated throughout you home, or workplace and the grime or blockage could cause your AC to run inefficiently. But there are more important issues that avoiding regular servicing could present…

    Excess moisture and unwanted particles inside your air conditioner can also lead to the growth of mould, mildew and bacteria and along with this there is the potential for harm to your health.

    A service visit really is the best option for this offending smell, as an experienced engineer is best placed to identify and fix the issue. Regular service and maintenance will prevent unwelcome stenches and ensure that your system is performing at its very best.

    8. Urine

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    As we have covered in previous points neglecting to regularly service your AC system will result in the presence of mould, mildew and bacteria.

    These micro-organisms will thrive happily within your air conditioning system, inside the coils, filters, and ductwork etc. In this damp, warm environment, they can multiple quickly, feeding off the trapped dead skin cells, hair and grime that can build up there over time.

    One odour that we commonly hear reported is that of urine.

    Moulds and bacteria are toxigenic, which means that they can produce toxins – specifically mycotoxins. If you detect a smell of urine, it means that these airborne toxins are not only present, but are being circulated around your home or workspace and potentially putting your health at risk.

    We would advise you to seek professional help as soon as possible. A qualified AC engineer will be able to quickly locate the problem, and eradicate the smell, using specialist equipment and cleaning products.

    A final word on smells …

    We have uncovered the most popular, or should we say unpopular, smells that you may detect coming from your air conditioner. You should now be able to sniff out their root cause and have a basic understanding of why this is happening.

    In simple terms, the odours that you can smell are either coming from your air con unit itself, from your AC systems ductwork, or are existing smells in your surroundings, that are being circulated.

    An air conditioner is a worthwhile investment, and it will help to keep your living or working environment comfortable for many years, but like most things mechanical, it needs regular service and maintenance, not only to keep it working safely and efficiently, but to also highlight any signs of wear and tear that need attention.

    Remember, prevention is better than cure, a badly maintained aircon system could result in the unexpected cost of an emergency repair. It could also be putting the health and safety of your loved ones, or colleagues, at risk.

    Always consult an expert if you notice anything untoward about your air conditioner, and never attempt to fix any of the issues of aircon smells yourself, unless you are qualified to do so.

    If you would like any further advise on how to deal with AC smells, or if you would like to speak to us about the installation, maintenance, or emergency repair of an AC system in your home or workplace, please contact our specialist team at Evergreen Air Conditioning Limited.