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How (& where) to position your air source heat pump

Posted by John Lightfoot on 6 June 2011 at 9:35 am

"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.

Looking to choose between an air source and ground source heat pump? Read our blog for guidance.

 

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.

More information about air source heat pumps

Get the best out of your air source heat pump in sub-zero temperatures

Using an air source heat pump with an exsisting system: 5 things to consider

Can you use radiators with air source heat pumps?

Are heat pumps cost effective?

Heat pumps information page

Find a heat pump installer

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.

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Comments

5 comments - read them below or add one

BrianVennard

BrianVennardComment left on: 7 January 2017 at 10:58 am

A year ago moved to a cottage on a retirement village with an Ecodan Heat Recovery Pump. Pump was installed inside a bin store attached to the front of the cottage on a metal framework buit into the brick walls without any vibration or sound pads. Noise and vibration terrible. Developer eventually inserted cork pads betwween the unit and metal Framework vibration reduced noise still unacceptable. Ecodan website features a noise reduction panel. Developer refuses to try installing this due to the loss in efficiency he says 55% but probably due to cost issues.

I would not buy a property with one of these units again.

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peedee

peedeeComment left on: 29 January 2015 at 9:54 pm

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I would have to contradict a statement made in Rule No.1 under particular circumstances :-

If you were to position your ASHP in the loft, … you would effectively turn that space into a cold room (freezer); …

 

By the same argument a 2kW fan heater might be expected to make a loft with uninsulated tiles toasty warm. Does that work?

 

My A2A heat pump is in my loft and I can assure the reader that this problem does not happen in my house. The first requirement is that the pump is small (up to 1kW(electrical)(5.5kW heat) as a rule of thumb). Second the loft has to be open throughout(my loft is 10x6m) and the thirdly the tiles(area about 100m^2) must not be insulated (usually done with sprayed foam).

 

The heat generated by the pump comes from the air that passes through the heat exchanger with a temperature drop of about 2 to 3C and from the electricity that drives the pump. The air in the loft is heated by heat coming off the ceiling insulation and through the tiles which is a large heat transfer surface. During the day the tiles absorb solar radiation (how would rooftop solar PV operate without this radiation?) and raise the loft temperature still further. My pump is rated at 0.45kW(electrical) but normally operates between 270 and 400watt, supplying up to 2kW of heat continuously 24/7.

 

Putting a heat pump in the loft offers other less obvious advantages :-

1: It keeps the pump out of the weather and clean, particularly important near coasts where salt spray can corrode the aluminium heat exchanger; dirty heat exchanger fins are a cause of inefficiency;

2: the pump dries the air in the loft and sends the condensate down the drain so that when the pump might start icing it doesn't; not having to defrost much saves money;

3: it is far less vulnerable to vandals and thieves;

4: it makes no audible or visual intrusion into the environment.

 

Mounting the pump correctly is important :-

1: It needs to be on a platform raised well above the ceiling joists for vibration isolation;

2: the air is also warmer higher up which benefits efficiency;

3: a raised platform allows the drain line to be run with a good fall to join a clean drain somewhere in the house, usually the upstairs bathroom; the shorter the run the better;

4: a drip tray under the pump is pretty much essential and the raised platform permits this to be fitted;

5: the drain line needs trace heating for freezing conditions and the blower unit also needs a drain for summer air-conditioning.

 

There is an assumption here that other forms of heating appliance are available to heat DHW, deal with extremely low temperatures and fast house heat from cold.

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Gary Thomson

Gary ThomsonComment left on: 18 December 2012 at 6:23 pm

I am considering making the plunge into the renewable energy field and have been having similar debate (with myself) as the one Chris highlights above and wondered if the input and output could be ducted in some way to take advantage of the heat generated in a polytunnel with say a thermal mass within as the input but then the output ducted off in the other direction to avoid overcooling the tunnel?

 

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JohnWL

JohnWLComment left on: 9 June 2011 at 9:58 am

Hi Chris,

It is difficult to say without seeing drawings, but I would guess the answer is likely to be, unfortunately, no.

Most of your heat requirement is likely to be in mid winter, when the Sun's radiation is at it's weakest and the number of hours it is above the horizon at it's shortest.

The problem will be that at night time in the winter when you are trying to take heat out of a box, albeit a very big box, which effectively will just keep reducing the temperature of the enclosure which in turn will reduce the efficiency of your heat pump.

Worth asking a local installer to take a look though as it is difficult to give a definitive answer with out seeing the polytunnel

I hope I am wrong!

 

 

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chrisevans

chrisevansComment left on: 8 June 2011 at 9:51 pm

I have an industrial size polytunnel approx 3 metres from my ext. wall (once used to house a swimming pool).  The temperature is obviously always significantly warmer in there than outside. In summer it is almost unbearably hot. Would it be practical to position an air-source heat pump within this structure with well insulated pipe runs?

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