"Where should I put my air source heat pump? is a question I am often asked.

I reply "where would you like to put it?" and nine times out of 10 it can be installed where the enquirer had hoped it could.

So let’s look at the basics to give us some ideas of where we can, and cannot, position our air source heat pump.

Rule No.1

An air source heat pump (ASHP), as it’s name suggests, requires air as its source of heat. So rule number 1 is position the unit where it has an ample supply of ambient (outdoor) air.

Note I mention ambient air. If you were to position your ASHP in the loft, garage or some other internal space you would effectively turn that space into a cold room (freezer); as the heat pump takes the same air and keeps cooling and cooling it until the temperatures slumped to levels where it was impossible for the heat pump to extract heat effectively.

Rule No.2

When having your ASHP installed always consider that, in that unlikely event that your unit should require attention, there is adequate access for a service engineer to take a look at it, without having to resort to expensive scaffolding or other access equipment.

So enough of rules and on to recommendations!

Ground Level or suspended?

Where ever possible I would recommend placing the unit on the floor immediately outside the property similar to the unit shown above. This has two major benefits: first, the pipework on the exterior of the house is kept to a minimum, thus avoiding increased heat loss. Secondly, any service or maintenance work is easily and comfortably executed.

I should also mention that if you are placing the unit on the floor, ample allowance should be made to ensure any ice caused by the defrost cycle in sub zero temperatures will not cause a hazard on a path or walk way – your installer will be well aware of this hazard and should be able to overcome it easily enough.

If you are fitting the unit into a corner made up of two walls, make sure there is adequate space around the unit to allow for free air flow. As an example the dimensions required for the units my company manufacture can be seen below.

You will notice that there is also a minimum distance that must be kept clear in front of the unit.
This distance is to prevent the cold air being blown out of the front of the unit from bouncing back into the rear of the unit.

Cold air bouncing back into the rear of the unit will reduce the average air temperature the unit is extracting its heat from, which in turn reduces the efficiency of the unit and increases running costs.

In some circumstances however it is not always possible to fit a unit on the ground and the unit must therefore be fitted on brackets at a higher level. If so, take care not to cause any hazard at head height and to ensure it is easily accessed for any service visits.

Again your installer will be able to advise you and will probably suggest a drip tray be used to ensure any condensate from the unit is collected and drained away out of harms way.

North, East, South or West?

I am also often asked whether there is any benefit in positioning the unit against a south facing wall rather than a north facing wall? Not normally, is my response!

As already mentioned the unit takes it’s heat from the air, and whilst it is possible that the shade air temperature may be a degree or so warmer on the south side of the property than the north, this is only likely to be in daylight summer hours when the unit is unlikely to be operating.

Other Considerations

If possible, avoid positioning the unit immediately outside or below a bedroom window. There are always those nights when you can not get to sleep and, if you are like me, when they occur the merest murmur like the refrigerator downstairs in the kitchen becomes an irritant.

While modern air source heat pumps are extremely quiet, in the middle of the night you are just as likely to notice them as you would the refrigerator in the kitchen downstairs if they are right outside your open bedroom window. Therefore the further away you put them from the bedroom window the more likely it will be that it is only the fridge’s murmur irritating you.

It is also probably worth also mentioning that you should avoid putting the unit into a court yard, where the sound would bounce around and not decay as quickly as when there are no surfaces for it to bounce on.

One final consideration, if your property is exposed, is to avoid positioning your unit against a wall that snow usually drifts against. If the snow was to drift against the unit and reduce its air flow, it would reduce its efficiency and its output as a result.

Flexible

So apart from the few exceptions I have mentioned above an air source heat pump can be positioned anywhere around the property, making it even more flexible than a traditional gas boiler and certainly, from a positioning point of view, one of the most flexible renewable energy technologies.

Next Blog – Can you use air source heat pumps to heat domestic hot water?

About the author: John Lightfoot is director at Thermal Energy Ventures Ltd.

If you have a question about anything in the above blog, please ask it in the comments section below.