Every summer I get the same call from pub groups, and it is almost never a broken machine. The cellar has crept up to sixteen degrees, the cask has gone cloudy, the cellar man swears nothing has changed, and somebody wants an engineer out that afternoon. We attend, and nine times out of ten the cooler is working exactly as designed. It was designed for a cellar that no longer exists.
Cellar cooling is one of the few pieces of refrigeration where the equipment is simple and the specification is where everything is decided. Get the sizing and the siting right and the box runs for fifteen years with a filter clean and a gas check. Get it wrong and you will be paying for call-outs forever, because no amount of servicing fixes a unit that was too small on the day it was fitted.
What a cellar cooling system actually is
Strip away the marketing and there are three arrangements in use across the UK trade.
A monobloc cellar cooler is a single box that sits through the cellar wall, evaporator inside, condenser outside. It is the standard fit for a single pub cellar. Nothing to route, one power supply, and any competent engineer can work on it.
A split system puts the evaporator in the cellar and the condensing unit somewhere else, usually a yard or a flat roof, joined by refrigerant pipework. You specify this when there is nowhere sensible to put a monobloc, when the noise would carry into a beer garden or a neighbour's window, or when the outside wall faces a street.
A remote condensing arrangement is the same idea scaled up, and it is what you want when one plant location has to serve a cellar plus a cold room plus a bottle store. Hotels and larger venues end up here. It costs more to install and it centralises the maintenance, which is usually the point.
| Arrangement | Best for | Watch out for |
|---|---|---|
| Monobloc cellar cooler | Single cellar, external wall available | Condenser discharges into a confined yard and recirculates its own hot air |
| Split system | No usable external wall, noise-sensitive sites | Pipe runs and height difference need designing, not guessing |
| Remote condensing | Cellar plus cold room plus store on one plant deck | One failure takes out several rooms unless the design allows for it |
How a cellar cooling system is sized
The heat load calculation is not complicated, but the inputs are where people guess. A cellar cooler has to remove everything that puts heat into that room, continuously, on the worst day of the year and not the average one.
- Fabric gain. Heat coming through walls, floor and ceiling. An old brick cellar under a pavement behaves nothing like a modern insulated room, and a cellar sharing a wall with a kitchen is fighting a losing battle before you start.
- Product load. This is the one that gets missed. Every cask and keg that arrives is at delivery temperature, not cellar temperature, and pulling it down is real work. A venue taking two deliveries a week has a different load profile to one taking six.
- Air change and door traffic. Every time the cellar flap or door opens you exchange cold air for whatever is outside. A busy Friday with the drop happening through an open pavement hatch is a heat load, not an inconvenience.
- Lighting and ancillary heat. Cellar lights left on, python pumps, glycol packs, the ice machine somebody moved down there because it was in the way upstairs.
- Ambient design temperature. If the condenser sits in a yard that hits thirty-five degrees in July, sizing it against a twenty-five degree ambient means it falls over exactly when you need it.
The number that comes out of that is a duty in kilowatts, and the unit you buy should have headroom on it. Not enormous headroom, because a wildly oversized system short-cycles, wears its contactors out and controls temperature badly. Sensible headroom, sized against the summer condition and the real delivery pattern.
The mistake that causes most of the summer calls
A cellar cooler specified fifteen years ago was sized for the trade the venue did then. Since then the site has added a second bar, moved to a bigger keg format, put in a kitchen next door, doubled the covers, and started taking a midweek drop it never used to take. Nobody re-ran the calculation, because nothing broke. The unit simply ran longer and longer each year until one hot week it could not catch up.
That is not a fault. That is a system at the end of its design envelope, and the honest answer is a re-specification rather than another repair. It is the same judgement we walk through in the repair versus replace decision.
The temperature you are actually designing for
Cask ale is the constraint. Cask Marque states that "the recommended dispense temperature of the majority of brewers is between 11 – 13°C", and that it "audits to a required range of 10-14°C allowing a little leeway". Keg and standard lager are dispensed colder, between 5 and 8°C, but that cooling happens in the python and the remote cooler, not by chilling the whole cellar down.
So the cellar itself is designed around that 11 to 13°C band. The practical consequence is that a cellar cooling system is a precision job with a narrow window, not a fridge. Four degrees of usable range is not much, and it is why systems that would be perfectly adequate on a cold room look marginal on a cellar. What pushes a cellar out of that band, and what to do about it, is covered in more detail in our guide to beer cellar temperature and why it drifts.
Six places cellar cooling specifications go wrong
These are the six we find repeatedly, in roughly the order of how often they turn up.
1. The condenser has nowhere to reject heat
Somebody puts the outdoor half in a light well, a bin store, or a narrow alley between two buildings. It works in April. In July it is breathing its own discharge air, head pressure climbs, capacity collapses and the unit trips on high pressure at four in the afternoon. Resiting it is the fix, and it is cheaper than the three call-outs that come first.
2. No allowance for the delivery
The system holds temperature beautifully until the drop lands, then takes eighteen hours to recover, by which point the next drop is due. This is a sizing failure dressed up as a performance complaint.
3. The cellar was never insulated
Cooling an uninsulated Victorian cellar is a permanent tax on the running cost. Insulating the ceiling and any wall shared with a warm space usually pays for itself faster than upgrading the plant, and it makes the plant that is already there adequate again. It is worth pricing both before assuming you need a bigger unit. The same arithmetic applies to refrigeration energy costs generally.
4. The thermostat is measuring the wrong air
A sensor sitting directly in the evaporator's discharge reads cold and satisfies the unit early, so the far end of the cellar sits three degrees warmer than the display says. We have measured six degrees of stratification in a long narrow cellar with one badly placed sensor. The paperwork said everything was fine.
5. Nobody thought about CO₂
Cellars hold gas cylinders, and CO₂ is heavier than air and collects at low level. A cellar is very often a confined space in practice. Gas detection and ventilation are a safety requirement in their own right, and they interact with the cooling design because ventilation is a heat load. Treating the two as separate projects is how you end up with a system that cannot hold temperature once the ventilation is doing its job.
6. Drainage was an afterthought
An evaporator makes condensate. If there is no fall on the drain, or it runs to a gully that backs up, the water ends up on the cellar floor under the stillage. Then somebody blames the cooler for a damp problem that is a plumbing problem.
What servicing should actually cover
A cellar cooling service that is worth paying for is not a visual inspection and a sticker. On a properly scoped visit an engineer should be doing the following.
- Cleaning the condenser coil properly, not blowing dust around it. A fouled condenser is the single most common cause of lost capacity.
- Checking superheat and subcooling, so a slow refrigerant loss is caught before it becomes a breakdown in August.
- Verifying the cellar temperature against an independent thermometer, at the far end of the room, not by reading the controller.
- Checking defrost is terminating properly, because a coil that ices progressively will hold temperature right up until it does not.
- Recording refrigerant type and charge, and carrying out any leak check the system's charge legally requires.
If that sounds like more than your current visit covers, it is worth reading what a planned refrigeration servicing scope should actually contain before you renew.
That last one has teeth. Under GB F-Gas rules, once a system holds 5 tonnes of CO₂ equivalent or more, mandatory leak checks and five years of records apply, and the duty sits with the operator, which is you and not your contractor. Most single cellar coolers sit below that threshold on charge alone, but a remote system serving several rooms often does not. Our guide to the UK F-Gas regulations sets out where the thresholds land.
Specifying cellar cooling across several sites
If you are buying for an estate rather than a single pub, the specification questions change. The equipment matters less than the consistency.
| Ask for | Because |
|---|---|
| A per-site heat load calculation, not a model number | Two cellars of identical volume can differ by 40% in duty once ambient and delivery pattern are counted |
| A standardised refrigerant and unit range across the estate | Spares, engineer familiarity and phase-down exposure all get simpler |
| Temperature logging, not spot readings | A spot reading proves nothing about last Saturday. This is the same argument as cold room temperature logging |
| Condenser location surveyed and photographed at tender | Half of the recurring faults on an estate are one badly sited outdoor unit repeated across ten pubs |
| A written scope for what a service visit includes | Otherwise "annual service" means whatever the cheapest bidder decides it means |
The single biggest saving available to a pub group is usually not a cheaper maintenance rate. It is finding the four sites that have been quietly failing every summer for six years and fixing the specification once.
Frequently asked questions
What size cellar cooling system do I need?
It comes out of a heat load calculation rather than off a chart. The inputs are the cellar fabric, the delivery pattern, door and hatch traffic, any equipment giving off heat in the room, and the summer ambient the condenser has to work against. Two cellars of the same volume can need meaningfully different duties once those are counted, which is why a model number quoted without a calculation behind it is a warning sign.
How long does a cellar cooling system last?
A well specified and maintained cellar cooler will typically give a long service life, but the practical limit is usually the refrigerant it runs on rather than the mechanical condition. Systems on older phase-down refrigerants become expensive to keep gassed well before they wear out.
Why is my cellar warm even though the cooler is running?
Most often a fouled or badly sited condenser, an undersized system that has been outgrown, or an iced evaporator with a defrost fault. All three present the same way, which is a unit that runs constantly and never reaches setpoint.
Can one system cool a cellar and a cold room?
Yes, with a remote condensing arrangement, and it is often the sensible choice when both rooms are near one plant location. It has to be designed as one system though. Splitting a cooler that was sized for one room across two is the most reliable way to end up with neither holding temperature.
Does a cellar cooler need an F-Gas leak check?
It depends on the refrigerant charge, not the size of the box. Once the charge reaches 5 tonnes of CO₂ equivalent, leak checking and record keeping become a legal duty on the operator. Your engineer should be recording the gas type and charge at every visit so you can answer that question.
Before you specify
The pattern in nearly every cellar cooling job we are called to is the same. The equipment is not the problem. The brief was. Somebody bought a unit off a size chart, put it where there was a hole in the wall, and nobody ever re-ran the numbers when the business changed underneath it.
If you are cooling cellars across more than one site and the same two or three keep coming back every summer, it is worth having the load calculations checked before you replace anything. Talk to us about cellar cooling and we will tell you which sites need plant and which ones need a better specification.
About the author: Ali Elm runs Be Cool Refrigeration & Air Conditioning, a family-run London firm that has been installing, servicing and repairing commercial refrigeration and air conditioning since 2004. His F-Gas certified team has delivered more than 2,000 projects across London and the South East.
Last updated: 12 August 2026
Written by
Ali Elm
Ali is the Head of Operations at Be Cool Refrigeration with over a decade of hands-on experience in HVAC and commercial refrigeration. He oversees every installation, repair, and maintenance project, making sure the work meets the highest standards. Ali holds full F-Gas certification and has worked across residential, commercial, and industrial refrigeration systems throughout London and the South East. When he is not on site, he writes these guides to help business owners and homeowners understand their cooling systems better.