Air-source heat pumps have incredible advantages. Highly energy-efficient, easy to install, no emissions. But what are the disadvantages of air-source heat pumps? In order to make an apt assessment of if a heat pump is a good investment, we have to look long and hard at the disadvantages of air-source heat pumps.
Here’s the short of it:
The benefits of using air-source heat pumps arguably outweigh their negative aspects. They can both heat and cool at an incredibly efficient rate.
Example: At −3 °C to 10 °C, many heat pumps run at a 3-3.5 coefficient of performance (COP). This means they generate 3 to 3.5 units of heat energy for every 1 unit of electricity they consume, significantly decreasing your utility bills.
Nonetheless, there are negative aspects to heat pumps as well.
In the midst of ‘Domestic Renewable Heat Incentive’ or ‘Clean Heat Grants’ for air-source heat pumps by the UK government, we made a list of all the cons these heat pumps bring.
We will look at all 8 downsides of air-source heat pumps in a systematic way. We will begin with a high upfront cost, and follow the disadvantages all the way to their noise generations and electricity dependence.
Here are the disadvantages of air-source heat pumps one-by-one:
1. High Upfront Cost (Biggest Downside)
Air-source heat pumps are very efficient to run but they cost a pretty penny to buy and install. Higher upfront costs are usually a major deterrent for homeowners thinking of getting one.
To illustrate: In the UK, a typical air-source heat pump can cost anywhere between £5,000 to £12,000 (with installation).
Prices of air-source heat pumps range from £2,000 to £6,500. The cost of the unit itself (outdoor unit + indoor unit + refrigerant lines) represents about 50% of the total cost. The other 50% cost is installation; which predominantly includes labour cost to install an air-source heat pump.
The actual total price of air-source heat pump installation in the UK depends primarily on:
- Size of the unit.
- Number of indoor units (air handlers). 4-zone air-source heat pumps are, for example, more expensive than 2-zone air-source heat pumps.
- Installation difficulty. To install a heat pump, an HVAC technician has to drill a hole in the wall for refrigerant lines (these connect the outdoor unit with indoor air blowers)
While the initial heat pump investment might set you back quite a lot, it’s advised that you think about air-source heat pump expenses in a time frame of 10 or 20 years. The electricity saves due to high energy efficiency far outweighs the negatives air-source heat pumps’ initial cost represents.
An award-winning UK blog about the renewable sources of energy Green Match offers free estimates on costs of air-source heat pumps. If you’re interested in a cost estimate, you can check the Green Match cost estimate calculator here.
2. Air-Source Heat Pumps Provide Lower Heat Supply Than Boilers
If you’re used to oil and gas boilers, you will find that air-to-air heat pumps provide less heat supply. That is a commonly cited disadvantage of air-source heat pumps.
With heat pumps, it is particularly difficult to heat up larger rooms and, by extension, larger houses.
To solve this con of air-source heat pumps, you might need:
- Big indoor air handlers.
- Larger radiators. If you have to install additional radiators or replace existing radiators with larger radiators, that will again incur some upfront costs of installing a heat pump heating system.
- Underfloor heating system. Many air-source heat pumps work best with underfloor heating. Of course, if you don’t have underfloor heating already installed, you will have to install it to reap the benefits.
Inadequately Insulated Homes Will Have Issues With Air-Source Heat Pump
The disadvantage of using air-source heat pumps in older UK homes is apparent as well. With the lower heat output of heat pumps compared to boilers, you would benefit from good insulation. That’s how the heat will be accumulated most efficiently.
Older UK homes with not as good insulation might suffer from lower temperatures in the winter as a negative consequence of using air-source heat pumps.
Despite the negative – lower overall temperatures – there is a positive side to this. The indoor temperatures are much more consistent when you’re heating your home with air-source heat pumps.
3. Lower Efficiency In Extremely Cold Weather
A known pitfall of air-source heat pumps is their inability to heat efficiently at very low temperatures.
Most heat pumps can have up to 300% efficiency (3.0 COP value) even at −3 °C, according to Wikipedia. On top of that, in mild UK weather, these air-source heat pumps can reach up to 400% efficiency (4.0 COP value).
However, a negative effect happens when outdoor air temperatures are far below the freezing point.
Due to the 2nd Law of Thermodynamics, the efficiency of most air-source heat pumps will fall to 100% (1.0 COP value) at about −18 °C. Below that temperature, heat pumps are rather inefficient because they cannot handle the outdoor/indoor temperature well enough.
That’s a major con for using ductless air-source heat pumps in very cold environments. Luckily, the United Kingdom has mild winters. You don’t see temperatures below −18 °C at all in most places like London.
That’s why this disadvantage is pretty much not as relevant in the UK. Moreover, the mild winters on the island are exactly why installing an air-source heat pump makes much more sense in the UK than in Scandinavia or Canada, for example.
4. Shorter Lifespan (About 15 Years)
Air-source heat pumps last for about 15 years. That is quite long but not as long as ground-source heat pumps; those have a lifespan of about 20 years.
The reason for the shorter lifespan of air-source heat pumps is easy to understand:
They are exposed to environmental factors. The outdoor unit (with the compressor) is exposed to all kinds of dirt, twigs, leaves, grass, insects, variable temperatures, and so on. This will generate more wear and tear than a ground-source heat pump is exposed to.
Of course, you can extend the lifespan of an air-source heat pump by committing to annual servicing. However, that does increase the maintenance costs of air-source heat pumps, doesn’t it?
Adding maintenance costs on top of the initial costs is another downside of air-source heat pumps.
5. How Noisy Are Air-Source Heat Pumps? Not The Quietest
In the past, air-source heat pumps were quite noisy. With improvements in compressors technology, the noise levels of modern heat pumps is significantly reduced, compared to the older units.
The key to understanding how noisy are air-source heat pumps is to divide the noise levels into two segments. Namely, we talk about the noise that the outdoor unit generates and the noise that the indoor air handler generates in the case of mini-split air-to-air heat pumps.
It’s commonly stated that air-source heat pumps generate 40 to 60 dB of noise. That’s only true for the outdoor unit. Here’s are the general noise levels for both units:
- Noise levels of the outdoor unit. This is a noisier part because it contains the compressor, and it may generate anywhere from 40 to 60 dB. Example of noise levels: 42/48/56 dB for Low/Mid/High speed setting.
- Noise levels of the indoor unit. This is the quieter part indoors. Indoor air handlers usually generate far less noise than outdoor units; even below 40 dB for all speed settings. The main noise generator is the airflow generation; you can hear your indoor air handler blowing hot/cold air. Example of noise levels: 29/32/36 dB for Low/Mid/High speed setting.
All in all, the loud air-source heat pumps are the issue of the past. That was usually thought of as one of the main disadvantages of heat pumps.
Modern ductless heat pumps are much quieter. The part that actually matters – the indoor air handler in air-to-air heat pumps – generates less than 40 dB even on high speed setting. The outdoor unit, containing the compressor, might be a bit louder.
6. Dependency On Electricity (Power Outage Issue)
All heat pumps run on electricity. In normal times, that’s not an issue. However, there are two major events when dependency on electricity can be viewed upon as a disadvantage of using electricity-powered air-source heat pumps.
- Power outages. In the event of a power outage, your air-source heat pump will go out as well as the same one your lights go out. With lights, you can always light a candle. With heat pumps, most households will not have an adequately sized alternative heating or cooling source to replace the air-source heat pumps’ function.
- Drastic increase in electricity prices. Heat pumps use relatively less electricity than other electricity-powered heaters (1,500W space heaters, for example) for the output they give. However, if electricity prices rise sharply, you will still be forced to use expensive electricity to run an air-source heat pump.
In such drastic events, it might be useful to have a home generator ready to generate electricity.
Nonetheless, if you compare furnaces and stoves to heat pumps, the heat pumps are at a disadvantage here because they only run on electricity, while furnaces and stoves can run on liquid fuels (heating oil, natural gas, diesel) or hard fuels (wood, pellets).
7. Planning Permissions To Install Outdoor Heat Pump Unit (Wales, Northern Ireland)
No one really likes to deal with planning permissions. In certain areas, you will need planning permission to install an air-source heat pump; that poses quite a disadvantage.
Here are the current special planning permission requirements in the UK:
- Air-source heat pumps in Wales. You are required to obtain planning permissions to install a heat pump.
- Air-source heat pumps in Northern England. You are required to obtain planning permissions to install a heat pump.
- Air-source heat pumps in England. In most cases, planning permissions are not required; it depends on the size and location of your home.
- Air-source heat pumps in Scotland. In most cases, planning permissions are not required; it depends on the size and location of your home.
For most UK homeowners, planning permissions are not required. However, if you live in an area where you will have to obtain specific planning permissions, you will have to satisfy the following requirements when installing the outdoor mini-split air-source heat pump:
- Outdoor unit should be installed at least 1 meter from your property’s boundaries.
- You will have to use a heat pump only for heating (no cooling allowed).
- Flat surface installation. You will have to install the outdoor unit on flat ground or flat roof.
- The total volume of the outdoor unit should not exceed 0.6 m3.
- If you live in a conservation area, you are not allowed to install an air-source heat pump.
Many homeowners might be dissuaded by the need for this planning permission. You have to take care of this issue of air-source heat pumps before you start the installation.
It is advised to check with your local offices what planning permissions you need. Based on requirements, you can choose the right size/position/installation for your heat pump.
8. Not The Most Appealing Look
A ground-source heat pump or a boiler is hidden from view. On the other hand, all air-source heat pumps require the outdoor unit to be installed, well, outdoors.
That means you have to deal with a giant (and often noisy) box outside your home. It must be said that that is not the most appealing look.
This is another stumbling block of air-source heat pumps.
All in all, the advantages of heat pumps in most cases outweigh the disadvantages. However, it is important you are aware of all the misgivings regarding air-source heat pumps before you choose to install one.
We hope this was helpful.