What is a storage combi? … So, you’ve read our previous blogs on the three different types of boiler system, and you think you’ve got it sussed.
You understand the differences between the three different types of boiler, and the pros and cons of each.
And then, we go and throw a spanner in the works, by telling you that there’s another variety of combi boiler – the storage combi.
Yes, you heard us right. Although a ‘combination’ boiler gets its name from the fact that it doesn’t need storage tanks or cylinders, everything it needs is in one compact unit, we’re now introducing you to the storage combi.
A storage combi has a hot water cylinder housed within the boiler unit itself, which means it is better suited to larger homes with multiple bathrooms.
If you want to understand the difference between combi and storage combis, read on!
What is a combi boiler?
Before looking at the ins and outs of the storage combi, it’s a good idea to start with a quick refresher on what a ‘normal’ combi is, so that you can see the differences between the two.
‘Combi’ is short for ‘combination’ boiler because it provides both your heating and hot water from one all-in-one (combined) unit; without the need for a separate cold water storage tank or an external hot water cylinder.
It’s important to point out that whilst combi boilers provide both heating and hot water, they can only perform one of these tasks at a time, and they always prioritise hot water.
A combi works by using two heat exchangers, one for your heating (radiators) and the other for your hot water supply.
The primary heat exchanger focuses on your radiators and carries hot water around your home. The secondary exchanger is for heating the water that comes out of your taps.
Combis can heat water directly from the mains when you turn on a hot tap so they don’t need to store hot water (unlike heat-only and system boilers), because they heat it instantaneously, on demand.
What are the advantages of a combi boiler?
The main advantages of combi boilers are that they:
- are space-saving because the boiler itself is the only component part.
- never run out of hot water because they make it on demand.
- can be more efficient due to not having stored water and being compatible with low temperature systems.
- have fewer third party components required.
- have more control options than a heat-only system.
What are the disadvantages of a combi boiler?
The main disdavantages of combi boilers are that they:
- have a slower delivery of hot water, so it takes longer to fill a bath.
- are generally unsuitable for larger homes.
- can be difficult to integrate with renewable energy.
- can’t be fitted with a back-up immersion heater in the event of a breakdown.
- are not suitable in low pressure water areas.
Read our blog on the pros and cons of combi boilers here.
What is a storage combi?
A storage combi is similar to a standard combi boiler; however it has a hot water cylinder housed within the boiler unit itself.
In this way, storage combi boilers combine the benefits of a combi boiler and system boiler all in one, whilst generally still being much smaller than a system boiler.
Storage combi boilers can be wall-hung or floor standing.
What sort of properties are best suited to storage combi boilers?
A storage combi is best suited to properties with a high demand for hot water but that lack space for an open vent or system boiler.
Storage combi boilers allow multiple outlets to be used at the same time, whilst still being space-saving.
Storage combi or ‘normal’ combi?
Combi boilers are generally a great choice in most situations, even in larger homes, and that’s why they’re the most popular choice of boiler in the UK.
Whilst there are many benefits to having a combi boiler, they’re not right for everyone. Combis are best suited to homes with relatively small hot water demands at any one time.
If you’re a household where everyone wants showers at the same time, then a combi won’t be suitable.
When thinking about how much hot water you need from your central heating system, a good starting point is looking at how many bathrooms you have.
Generally, homes with multiple bathrooms have a higher hot water demand.
What is your hot water demand?
If you have two or more bathrooms, and want to have two showers running at the same time, a standard combi will struggle to meet your needs.
This is because they don’t store hot water and so the hot water that they are generating on demand is having to be split to two outlets, lowering the flow rate.
This won’t be an issue if your household takes it in turn to shower though because a combi has no problem supplying unlimited hot water to one outlet at a time.
Combi boilers will never run out of hot water because they heat water instantly on demand; unlike heat-only and system boilers, that might run out of hot water for a short time while the cylinder refills.
So, this is where it’s important to consider how you use the hot water in your home.
If you want to have more than one shower running at the same time in the morning, then you need a boiler that stores hot water, because they can supply multiple outlets at the same time.
If you don’t have the space for a heat-only or a system boiler, a storage combi might be a good option for you.
What are the advantages of a storage combi boiler?
Because storage combis have a hot water cylinder within the unit itself; you won’t need extra space in a cupboard and/or your loft to house any additional tanks and cylinders.
Can supply hot water to multiple outlets at the same time
If a combi boiler appeals to you, but you have a high demand for hot water, a storage combi could be a good option.
Since storage combis store hot water, they are able to supply multiple hot taps at the same time, which is perfect for larger families who all want to be using the hot water at the same time in the morning.
Storage combis are cheaper than system boilers
Storage combi boilers are generally cheaper to purchase and install than system boilers. This is because there is less pipework required and because the system itself is generally smaller.
Storage combis are compatible with solar thermal options
What are the disadvantages of storage combi boilers?
As with all things, there are drawbacks too:
More expensive than standard combi boilers
Storage combi boilers are generally more expensive than standard combi boilers because they have the added feature of the internal hot water storage cylinder.
Bigger than standard combi boilers
Although storage combi boilers are smaller than system boilers, they are larger than standard combi boilers. This is due to the fact that they need to house a hot water cylinder within the unit itself.
Different models of storage combi boilers have a different hot water capacity
As you would expect, the size of the hot water cylinder determines the capacity of the boiler, and how much hot water it will be able to supply your multiple outlets with before it needs to refill.
Each model of storage combi varies in cylinder size, so you need to check that you choose one that will meet your hot water demands.
Storage combis can sometimes have a reduction in flow rate
A storage combi can comfortably supply a larger home with multiple bathrooms with up to 25 litres per minute of hot water.
However, if you have three or four people all using hot water at the same time, you might notice a reduction in flow rate. If this is an issue for you, you might be better considering a system boiler – more on this below.
Will I need extra storage space for a storage combi?
Although bigger than a standard combi boiler, the main benefits of a storage combi is that it doesn’t require an external hot water cylinder.
They are relatively compact and generally much smaller than system boilers. You can install a storage boiler in your home, without the need for extra storage space in cupboards or your attic.
Would a system boiler be a better option than a storage combi?
If you’re considering a storage combi, you should also look at whether a system boiler is a good option for you.
System boilers feature aspects of both a conventional or ‘heat-only’ boiler and a combi boiler.
Like a conventional boiler, a system boiler needs a hot water storage cylinder to heat and store hot water for your taps. But it doesn’t need a tank in the attic because, like a combi, it takes its water supply directly from the mains.
System boilers are high-pressure systems which can provide all the heating and hot water your home will ever need, direct from the mains, with no reduction in flow rate.
What are the advantages of a system boiler?
- work well in large households with multiple bathrooms.
- can supply large amounts of hot water to multiple outlets at the same time.
- don’t require as much space as conventional boilers.
- can be fitted with an additional electrical immersion heater to provide you with back-up hot water in case your boiler ever suffers a breakdown.
- are easy to integrate with renewable heating systems such as solar.
- have a wider range of control options available, compared to conventional boilers.
- can be installed to low temperature, high efficiency heating systems.
What are the disadvantages of a system boiler?
- require more space than a combi boiler.
- have a lack of instant hot water – takes time to heat, although this can be minimised with the correct controllers.
- can run out of hot water if controls are not set up properly.
You can read more on the pros and cons of system boilers here.
The Heating People generally use ATAG system boilers due to the advanced control options available; high build quality; and relatively low cost.
If you have a high demand for hot water and are struggling with choosing between a storage combi and a system boiler, contact one of our experts at The Heating People, who can give you tailored advice.
You might also like to read our related blog: 6 Top tips for buying a new boiler.