The short answer
Wall brackets fix the outdoor unit to a sound wall and keep the ground clear, while ground stands hold it on a firm, level base. Both should raise it clear of water, snow and debris and sit it on anti-vibration mounts.
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What holds the outdoor unit up matters more than it looks. The mounting affects how much vibration reaches your home, how easily the unit can be serviced, and whether defrost water drains away or freezes around it.
Wall brackets
Wall brackets are a pair of steel arms, usually galvanised or powder-coated against rust, bolted to the wall. The unit sits across the arms and is bolted down to them.
Outdoor units for homes often weigh several tens of kilograms, so the fixings matter. A good installer chooses them to suit the wall:
- Solid brick or block. Heavy-duty anchors into sound masonry rather than the mortar joints.
- Soft or crumbling older brick. Resin anchors, which bond into the masonry around them.
- Cavity walls. Fixings go into the outer leaf, which needs to be in good condition.
- Rendered or externally insulated walls. Longer fixings or brackets designed to reach through to the masonry behind.
- Timber-frame or clad walls. Fixing into the structure, or a ground stand instead.
Brackets suit spots where ground space is tight, such as a narrow passage or above a flower bed, and they lift the unit out of the way of knocks, leaves and snow.
The drawback is vibration. A wall passes it into the house more readily than the ground does, so where possible brackets are kept off bedroom walls and off walls shared with a neighbour. A high position keeps the unit out of the way but makes every service or repair harder, sometimes needing a tower or scaffolding.
Ground stands
A ground stand holds the unit up off the ground. The common types are:
- Rubber or plastic feet. Low, simple blocks that sit on a flat base.
- Steel frames. Taller, sometimes with adjustable legs, lifting the unit higher above snow and puddles.
The stand needs a firm, level base such as paving slabs or a concrete pad. Soil and lawns settle and loose gravel can shift, so a unit placed straight onto them can end up tilted. The unit is bolted to the stand, and in exposed spots the stand itself may need securing so strong wind can't move it.
A ground position is usually easy to service and passes less vibration into the house. It does take up space, can be knocked by bins, bikes or mowers, and needs keeping clear of leaves and plants, as covered in looking after the outdoor unit.
On a flat roof, stands spread the load and sit on protective pads so the roof covering isn't damaged. In England, a unit on a flat roof must be at least 1 metre from the edge to stay within permitted development.
Comparing the two
| Consideration | Wall brackets | Ground stand |
|---|---|---|
| Space | Keeps the ground clear | Needs ground space |
| Vibration | More reaches the house | Less reaches the house |
| Servicing | Harder when high up | Usually easy |
| Suits | Sound masonry walls | A firm, level base |
| Watch for | Bedroom and shared walls | Knocks, leaves, snow |
Anti-vibration mounts and levelling
Whichever is used, the unit should sit on rubber anti-vibration mounts. The compressor and fan vibrate slightly as they run, and the mounts stop that passing into the bracket, wall or ground as a hum you can hear indoors.
The unit should also be level, or within the manufacturer's allowance. A unit that isn't level can drain poorly and may not run as intended.
Over time, rubber mounts can perish and fixings can loosen. A service is a good moment to check them.
Water, noise and covers
Raising the unit clear of the ground lets defrost water drain away from its base instead of freezing and building up ice underneath. It also keeps the unit above snow, leaves and standing water, and some manufacturers give a minimum height for cold or snowy areas.
Think about where the water lands. Brackets above a doorway, step or path can leave ice underneath in winter. The options for dealing with it are in where the water goes.
The mounting also changes the noise calculation used under planning rules in England. Each hard surface close to the unit, such as the ground or a nearby wall, counts as a reflecting surface and adds to the level at a neighbour's window. That's how a unit tucked into a corner can come out louder than one on an open stretch of wall, as explained in noise rules and your neighbours.
Decorative covers and cages must leave the airflow as clear as the manufacturer requires. Under permitted development in England, the outdoor unit including any housing must be no more than 1.5 cubic metres.
Related guides
- Where the outdoor unit can goAn outdoor unit needs a firm fixing, free airflow, service access and somewhere for defrost water to drain. On a house in England it can usually go on a wall, the ground or a flat roof without planning permission if set conditions are met.
- Looking after the outdoor unitKeep the space around it clear so air flows freely, brush off leaves and snow with the system switched off, and leave cleaning the coil and anything inside the casing to an engineer. Otherwise it needs little beyond its regular service.
- Where the water goes: condensate drainageWater that condenses in the indoor unit as it cools runs through a drain hose to a suitable outlet, with a small pump where it can't fall naturally. In heating mode the outdoor unit produces water too.
- Noise rules and your neighboursIn England, a heat pump fitted without planning permission must be no louder than 37 dB(A) at 1 metre from a neighbour's nearest habitable-room window or door, worked out with the MCS 020(a) calculation. Councils can also investigate noise complaints separately.