How to enclose an outdoor unit without losing performance

Enclosing an outdoor unit is only worth doing if it does not come at the cost of how the unit works. Air conditioners and heat pumps give off or take in heat by exchanging air with their surroundings, so anything that restricts that flow shows up in performance, energy use and noise. The good news is that looks and performance can be reconciled, as long as you stick to a few rules.

How an outdoor unit works

An outdoor unit draws air in through the sides or the back and blows it out through the front grille with the fan. The heat exchanger gives heat up to that air (in cooling mode) or takes heat out of it (in heating mode). For the process to work efficiently, the unit needs access to fresh air and a clear way out for the air it has already used.

The main risk: recirculation

The most common problem with a badly designed enclosure is recirculation: the unit drawing back in the air it has just blown out. It happens when the cover is too tight or closed on every side. The unit starts “circling” in its own air, which means it:

• runs longer to achieve the same result,
• uses more energy,
• runs more loudly,
• wears out faster.

An enclosure that eliminates this comes down to a single principle: air must have somewhere to come from and somewhere to go.

The rules of a good enclosure

1. An open back

The back of the unit, which is usually where air is drawn in, should stay exposed. Lamelvio covers are open at the back in every version, whatever the extent of the enclosure you choose.

2. A gap between cover and unit

The cover must not touch the unit. There has to be space between the two for air to circulate freely. How big that gap should be depends on the model of the unit and its manufacturer's recommendations, which is why it is set individually at the design stage.

3. Open slats rather than a solid wall

If you go for a slatted cover, leave a gap between the slats. The narrower the gap, the more thoroughly the unit is screened, but the less air gets through. Choosing the slat width and the spacing is a trade-off between concealment and ventilation, and it is settled for each particular unit.

4. A clear outlet at the front

The fan grille at the front blows out a stream of air. Do not put a solid panel right in front of it and send that stream straight back. With a front made of slats or a panel with cut-outs, the air has somewhere to escape.

5. Access for servicing

An enclosure should not make cleaning and servicing impossible. Plan it so that you can still reach the unit, its valves and its connections. If you need particularly easy access from one specific side, say so in your enquiry.

What else affects performance

• Where the unit sits. A narrow passage between buildings, the angle between two walls or a recess all encourage warm air to collect. In spots like these an open, airy cover matters all the more.
• Dirt and debris. Leaves, pollen and dust settling on the heat exchanger reduce performance. A cover with a panel on top limits how much gets in, but it does not remove the need for periodic cleaning.
• Direct sun. A unit baking in the sun works in harder conditions. A cover provides some shade, as long as it does not close off the airflow at the same time.

What this looks like in practice with a made-to-measure cover

Because the cover is built for a particular model of unit and a particular spot, the gaps and the extent of the enclosure are matched to the situation. It helps to give us the make and type of the unit, its dimensions and photographs of the installation spot with your enquiry. On that basis the design takes care of both screening the unit from view and leaving a path for the air.

The most common mistakes

It pays to know the typical slip-ups, because most of them come from wanting to screen the unit “properly” at any price:

• A sealed box. An enclosure closed on every side is the shortest route to recirculation and higher bills.
• A cover pressed against the unit. With no gap, airflow is blocked and servicing is awkward.
• A solid panel in front of the fan. The stream of air bounces off it and goes straight back into the unit.
• An enclosure in a tight corner with no ventilation. The angle between walls or a narrow passage traps warm air, and that is exactly where open slats matter most.
• No access for servicing. If you cannot reach the unit once the cover is up, every clean or repair becomes a problem.

Ventilation and good looks are not at odds

The usual assumption is that the tighter the screen, the better it looks. In practice the opposite is true: a well-designed open cover looks neat and breathes at the same time. Choosing the slat width, the gaps and the extent of the enclosure gets you a visually clean result without choking the unit. That is precisely why a made-to-measure cover works better than an off-the-shelf enclosure.

In summary

Enclosing an outdoor unit need not cost you performance, as long as you keep the back open, leave a gap between cover and unit, use open infill and keep the outlet at the front clear. The worst thing you can do is shut the unit in a sealed box. A made-to-measure cover, designed around a specific unit, lets you combine a tidy facade with an air conditioner or heat pump running at full tilt.