5 Common Air Conditioning Mistakes That Could Be Costing You Money

When temperatures rise, most of us turn straight to the air conditioning without a second thought. But what many homeowners and employers don’t realise is that running an AC system the wrong way can quietly drain hundreds, even thousands, of pounds a year. 

If you’re a family trying to keep your home comfortable, or a building owner responsible for tenants and staff, knowing the most common mistakes is the first step to saving money. Let’s look at the five that cost people the most and how to avoid them.

At DevineAir, our expertise in achieving and maintaining compliance ensures a safer working environment for families, clients, and their staff. You can trust our guidance to navigate the complexities of AC maintenance.

5 Costly Air Conditioning Mistakes to Avoid

Air conditioning keeps homes and workplaces comfortable, but small mistakes can drive up your bills. Avoiding these five common errors can save you money and extend your system’s life.

1. Skipping Legally Required TM44 Inspections

If your building’s air conditioning system has a combined cooling capacity over 12 kW, you’re legally required to have it inspected every five years under the Energy Performance of Buildings Regulations.

• For families: Most homes won’t reach this threshold. But if you’ve installed multiple large split units, it’s worth checking, especially in bigger properties.
  
• For employers/building owners: This is non-negotiable. Failing to get a TM44 inspection could leave you non-compliant, risk fines, and increase running costs because inefficiencies go unchecked.

Why it costs you money: Inspections highlight problems such as poor control settings, leaking refrigerants, or oversized systems that waste energy. Without them, small faults often grow into expensive breakdowns.

How to fix it:

• Book your inspection with an accredited energy assessor.
• Use the assessor’s report as a roadmap to reduce waste and improve efficiency.
  

2. Ignoring Passive Cooling Before Turning the AC On

One of the most common mistakes is relying on your AC for every bit of cooling, even when cheaper, low-tech options could do the job.

• For families: Leaving curtains or blinds open on a hot day means your AC has to fight against unnecessary heat gain.
• For employers: Allowing heat from office equipment or open windows to mix with cooled air forces your system to work harder, increasing electricity costs.

Why it costs you money: Running your AC unnecessarily for even two extra hours a day in summer could add hundreds of pounds to your annual electricity bill.

How to fix it:

• Use blinds, shutters, and insulation to limit heat gain.
• Encourage staff at work to close doors when the AC is running.
• Open windows in the evening to release built-up heat before turning the AC back on the next day.

3. Choosing the Wrong Type of System

Many households and small businesses buy portable air conditioners because they’re cheap upfront. While a portable unit may cost just £150–£250, running costs are nearly double those of a fixed split system.

• For families: A portable unit might be enough for a single bedroom, but for whole-home cooling, it’s an expensive compromise.
• For employers: Relying on portables in offices is a false economy. They’re noisy, less efficient, and often leave staff uncomfortable — which impacts productivity.

According to MoneyWeek, a portable AC can cost about £22 per week to run, while a fitted system can be closer to £10–11 per week.

Why it costs you money: Short-term savings on the purchase price are outweighed by higher electricity use, noise complaints, and shorter lifespan.

How to fix it:

• Assess your long-term cooling needs. If you’ll be using AC regularly, an installed system will save money overall.
• For businesses, calculate the cost per employee or per square metre to see the real value of a permanent installation.

4. Overlooking Grants and Incentives

The UK government’s Boiler Upgrade Scheme currently offers up to £7,500 to households and businesses installing heat pumps. Air-to-air heat pumps, which provide both heating and cooling, may soon be included, following a public consultation.

• For families: A heat pump could replace both your boiler and your AC, slashing bills in the long run.
• For employers/building owners: Large properties with high cooling demand could see major savings by switching to a system eligible for grants.

Why it costs you money: If you stick with traditional AC and overlook available funding, you could miss out on thousands in government support.

How to fix it:

• Check eligibility for grants under the Boiler Upgrade Scheme.
• Keep an eye on upcoming government announcements — new funding for air-to-air heat pumps may be rolled out from 2026.
• Factor grants into your long-term investment plan for building energy systems.

5. Neglecting System Size, Maintenance, and Insulation

Even the best AC system will waste money if it’s the wrong size, poorly maintained, or battling against a badly insulated building.

• System size: An oversized unit will cycle on and off too often, while an undersized one will run continuously. Both drive up energy costs.
• Maintenance: Dirty filters, blocked vents, and low refrigerant levels reduce efficiency by 5–15%.
• Insulation: Without proper insulation, cooled air leaks out and hot air seeps in — making your AC work overtime.

According to the Great British Insulation Scheme, households could save £300–£400 per year on bills simply by upgrading insulation.

Why it costs you money: A poorlyy maintained or mismatched system not only wastes energy but also shortens the life of your unit, leading to costly replacements.

How to fix it:

• Schedule annual servicing for all AC units.
• Replace or clean filters every 1–3 months.
• For building owners, set up a maintenance contract with clear responsibilities.
• Invest in insulation — the benefits extend beyond cooling, helping in winter too.

The Link Between Air Conditioning and Indoor Air Quality

Air conditioning doesn’t just control temperature but also has a big impact on the air quality your family, employees, or tenants breathe every day. A well-maintained system filters out dust, pollen, and other airborne pollutants. But when filters are clogged or systems are neglected, the opposite happens: allergens, bacteria, and mould can circulate throughout the space.

For families, this can mean children suffering from allergies, asthma flare-ups, or general discomfort at home. For employers and building owners, poor air quality can lead to reduced productivity, increased absenteeism, and even potential health complaints from staff.

Another factor is humidity. A functioning air conditioning system helps balance moisture levels in the air. Too much humidity can cause mould growth and damage to building materials, while air that’s too dry can irritate skin and the respiratory system. Striking the right balance ensures a healthier, more comfortable environment for everyone.

Regular servicing, including filter replacements and duct inspections, ensures your AC isn’t just cooling the space but actively supporting healthier indoor air quality. This is especially important in workplaces, schools, and healthcare settings where indoor air plays a direct role in well-being and performance.

Stop Letting Poor Ventilation Drain Your Wallet

Air conditioning should make life easier, not more expensive. By avoiding these mistakes, you can cut costs, extend the life of your system, and create a healthier environment for your family or employees.

At DevineAir, we help homeowners, employers, and building managers take control of their air quality and efficiency with expert testing, maintenance, and tailored solutions. If you’re ready to save money while improving comfort, our team is here to help. 

Ready to cut costs and improve your indoor air quality? Contact DevineAir today for expert air conditioning and ventilation assessments that keep your home or workplace comfortable, healthy, and efficient.