Monobloc or Split Air Source Heat Pump?
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Summary: Is A Split or Monobloc Heat Pump Better?
Monobloc air source heat pumps are more popular than split heat pumps in the UK.
Whilst there are small benefits available when using a split unit (slightly better efficiency and lower chance of pipework freezing), they’re offset thanks to split heat pumps:
- Being more complex and expensive to install
- Requiring both indoor and outdoor space
- Having a higher maintenance cost (two units need to be serviced as opposed to just one)
We fit a range of monobloc heat pumps from leading brands such as Vaillant, Ideal and Grant.
Find the most suitable unit for your property by using our 2-minute clickable heat pump tool here.
How Monobloc Heat Pumps Work
A monobloc heat pump works by compressing the refrigerant, when it is in a gas state, to increase its temperature. The heat from the refrigerant (usually R290 or R32 these days, since R410a is being phased out), passes to the water, which is then passed to the water in the central heating radiators / underfloor heating or the water in your hot water cylinder. These systems can extract heat from air even in very cold temperatures.
Installation is simple due to the fact that refrigerant is contained within the monobloc unit. Pipework connecting the system to your hot water and heating only contains water.
How Split Heat Pumps Work
A split heat pump is not a self contained unit. You'll have an external unit, but also an indoor unit which is sometimes called a hydrobox.
The outdoor unit tends to house the heat exchanger for the refrigerant, as well as the compressor. And whereas refrigerant is contained within a monobloc system, it's not with a split system.
Instead, the heat transfer happens via refrigerant that is carried into the home via pipework. At this point a secondary heat exchanger helps to transfer the heat from the refrigerant to hot water and heating systems.
Whilst split heat pumps are more complex and expensive than monobloc heat pumps they offer a range of benefits. These include reduced risk of pipework freezing and higher efficiency, as well as being able to position the heat pump further from the house (if that was a necessity).
Monobloc vs Split Heat Pumps
Installation Complexity
Monobloc heat pumps are typically much easier to install than split heat pumps. This is simply because monobloc systems have just one unit, usually located outdoors.
Split units (as the name suggests) have an outdoor and indoor unit. Not only do two units need to be installed, but they also need to be connected together via pipework.
With monobloc systems, whilst they do have refrigerant in them, it’s sealed; there’s no “refrigerant work” required, so your engineer won’t need to be F-gas certified.
For split heat pump systems, your engineer will need to be F-gas certified to connect, test and commission your system.
And the work doesn't stop there. Your heating engineer will have to plan for condensate drainage indoors, something which isn't required when using a monobloc heat pump.
Overall, a split heat pump is the more complex of the two units to install, and that means it’s going to be much more expensive.
Space
Air source heat pumps are much larger than gas boilers. For instance, the Ideal Logic Plus gas boiler is 700mm x 395mm x 278mm.
Compare that directly to Ideal's own air source heat pump - the Logic Air - which is approximately 1095mm x 520mm x 1000mm.
Luckily, monobloc heat pumps are installed outdoors. As long as you have a small amount of outdoor space, the size isn’t going to impact you.
However, a split heat pump will need space for an outdoor unit and an indoor unit. A typical indoor unit is similar in size to a gas boiler, but they can vary.
Short on internal space? You'll want a monobloc air source heat pump system.
Maintenance Cost
Expect a split heat pump to be more expensive to maintain in comparison to a monobloc equivalent. Like installation complexity and space requirements mentioned above, this is simply due to the split system using two separate units.
With a monobloc using one external unit it can be maintained, serviced and repaired without an engineer even entering your home. This isn’t the case with a split unit and an engineer will need to service two units, not one.
Expect the maintenance cost of a split heat pump to be nearing twice the cost of a monobloc heat pump.
Why Would I Install A Split Heat Pump?
Monobloc heat pumps are the go to units in the UK. However, there are instances where it makes sense to install a split heat pump instead.
Which is The Best Monobloc Air Source Heat Pump?
There are dozens of heat pump manufacturers operating in the UK.
If you're looking for a reliable heat pump with high efficiency ratings and a long warranty, we'd suggest units such as the:
Use our heat pump configuration tool to determine a suitable size of heat pump for your property