An open-fronted unit is exchanging air with the street all day. A cassette sized as if the front were a closed door will run continuously and still miss a setpoint at the threshold. Cool the zone you can actually hold: the till, the staff standing area, and any enclosed room at the back. An air curtain on the opening reduces the river of outdoor air. Be honest about the opening hours and the opening width on the survey, because that honesty is the running-cost decision.
The shutter up from 9am to 6pm
Width, height and how long the front stays fully open dominate the calculation. Awnings, a lobby or a partial screen change it. A heatwave afternoon with sun on the pavement changes it again. If the surveyor is not told that the shutter stays up from 9am to 6pm, the quote is fiction. State the hours the front is open. Expect higher running cost than a closed shop of the same floor area.
The till you can hold and the pavement you cannot
Spot cooling for people can still be worth having. Staff standing in a hot unit are a workplace comfort issue under HSE guidance, which expects reasonable temperature and does not offer a legal maximum. The aim is a better local environment, not a cold pavement. Several smaller indoors aimed at people often beat one oversized cassette roaring at the street. A back-of-house office or store can be a closed room with a normal split. The open sales area gets the curtain and whatever cooling the energy bill can justify. Condensers on a rear wall still need access, a drain for defrost water, anti-vibration mounts and a planning or lease check. F-gas certification applies. GOV.UK publishes that certification. If you add enough capacity to cross the GOV.UK inspections threshold, put that duty on the operator from day one.
Mid-20s while you trade, off when the shutter drops
A setpoint in the mid 20s, with air movement for staff, survives contact with an open front better than 18C. The lower figure invites continuous running and complaints that the unit is faulty when it is simply fighting the street. Write the policy on the staff notice, not only in the manual. Close the front when you are not trading. Night setback or a full off outside opening hours is the obvious saving. A unit left to chase 20C until midnight with the shutter up is a controls failure. Energy Saving Trust's explanation of air-to-air heat pumps is a useful reminder that these machines move heat well in a closed room and cannot repeal an open facade. Use them where the room is real. Use an air curtain as a door tool, not as a substitute cassette.
Frequently asked questions
Can we fully air condition an open shopfront?
You can throw a great deal of cooling at it and still track outdoor temperature at the threshold. Design for the zone you can hold, and treat the opening with a curtain or a physical screen if you need more.
Will a bigger cassette solve it?
A larger unit moves more heat and uses more electricity. Without a limit on the opening it still may not hold a setpoint. Change the brief before you only change the kilowatts.
Is an air curtain mandatory?
No. It is a practical tool for open doors. Some units are better served by a partial screen or by accepting a limited cooled zone. The survey should compare those options.
What should staff be told about the setpoint?
A setpoint in the mid 20s, with air movement, survives an open front better than 18C. Write that policy on the staff notice. Close the front when you are not trading. HSE expects reasonable workplace temperature and does not set a legal maximum.
What running-cost comparison is honest?
As a 2026 illustration, the extra electricity for an open front in a hot month can exceed the price gap between two equipment grades. A frank design that cools a smaller zone can cost less to install and less to run than a heroic plant that never catches up. Ask for both options.
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How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.