Heat-only boilers are a good choice for larger households with multiple bathrooms because they can meet a high demand for hot water.
Somewhat confusingly, they’re known by a few different names.
You might know heat-only boilers as ‘regular’ or ‘conventional’ boilers. These names reflect the fact that they’re often viewed as the traditional way of heating a home.
In the industry, they’re commonly referred to as ‘heat-only’ boilers, because they produce hot water for your central heating, but use a separate hot water cylinder to produce hot water for your taps, baths, and showers.
In this blog, we’ll explain what a heat-only boiler is, and discuss their major pros and cons. Hopefully this will help you to decide whether a heat-only boiler might be a good option for you.
What is a heat-only boiler?
When you’re considering replacing your boiler; one of the first things that you’ll need to decide is what type of boiler you want.
There are three main types of boilers that you can choose from: combi boilers; system boilers; and heat-only boilers.
Combi boilers are compact all-rounders that produce both your heating and hot water from one unit; without the need for external tanks or cylinders. This makes them a popular choice for homes that are short on space.
A system boiler provides your heating and hot water using the boiler itself; and an additional cylinder for storing hot water.
A heat-only boiler provides heating directly to your central heating, and works with a cylinder to provide your hot water. They can be ‘open-vented’, meaning that there’s a feed and expansion tank in the loft. But they can also work on a ‘sealed’ system too.
How do heat-only boilers work?
Heat-only boilers are usually installed as part of an open vented system.
In addition to the boiler itself, there is a cold water cistern (sometimes called a header tank); a small feed and expansion tank; and a hot water storage cylinder.
The cold water cistern and the feed and expansion task; are installed in the highest part of the home (usually a loft or attic). And the hot water cylinder is usually installed in an airing cupboard.
The cold water cistern receives its water from the mains. With the help of gravity, it supplies the cylinder with cold water which is then heated by the boiler.
The hot water is stored until it’s needed to heat your radiators or supply your taps and showers.
The purpose of the feed and expansion tank is to maintain the correct level of water for the heating system. It allows for the water expansion when the heating is switched on.
Let’s look at how heat-only boilers are different from the other two types of boiler.
How are heat-only boilers different from system boilers?
Heat-only boilers are sometimes confused with system boilers because both boilers store large quantities of hot water in a cylinder.
The key difference between them; is that a heat-only boiler is supplied with cold water from the storage cistern (usually kept in the loft). Whereas a system boiler takes its cold-water supply directly from the mains.
Both heat-only and system boilers are good options for homes with a high demand for hot water. Because they store hot water and can therefore support multiple outlets being used at the same time.
You might like to read our related blog: Pros and cons of system boilers.
How are heat-only boilers different from combi boilers?
A combi boiler is different from heat-only and system boilers because it’s an all-in-one unit. It doesn’t need any external tanks or cylinders.
A combi takes its cold-water supply directly from the mains and heats it instantaneously on demand.
Since combi boilers don’t have a large store of hot water; they’re generally better suited to small to medium-sized homes which use less hot water.
You might like to read our related blog: Pros and cons of combi boilers.
Pros of heat- only boilers
Despite being one of the oldest types of boilers, heat-only boilers still offer lots of benefits for home heating:
Pro: Heat-only boilers can meet high demand for hot water
The main advantage of heat-only boilers is that they can meet a high demand for hot water.
Combi boilers struggle where different family members want to shower or use hot water at the same time. This is because combis heat water from the mains instantly on demand.
Unlike combi boilers, heat-only boilers store a large quantity of hot water in a cylinder. So, they’re able to supply multiple taps and bathrooms at the same time, without losing pressure. As such, they’re a good choice for larger households and commercial premises.
Pro: Heat-only boilers are effective in areas with low pressure
Heat-only boilers are also a good choice in areas with low water pressure. This is because the cold-water cistern (usually installed in the loft) feeds the cold water to the boiler by gravity.
Gravity-fed systems don’t need good water pressure to work. This makes heat-only boilers an ideal choice for regions where the water pressure is too low for a combi boiler – which is fed directly from the mains supply.
Pro: Heat-only boilers are compatible with renewable technology such as solar power
Another advantage of heat-only boilers is that they can be integrated with renewable heating systems. This can save you money whilst helping the environment.
Solar thermal heating systems use free heat from the sun to heat your water; rather than burning gas which you have to pay for.
If you’ve read our blogs on what the government is doing to tackle climate change; and the outcomes of COP26; you’ll know that the increased use of renewables is vital in our ambition to achieve Net Zero.
Pro: Heat-only boilers are compatible with immersion heaters in case of a breakdown
Another bonus of having a heat-only boiler over a combi; is that it can have an electric immersion heater fitted to its hot water cylinder.
An immersion heater is an element that goes inside the cylinder and heats it up. It can act as a backup and heat your water instead of your boiler. This is handy because it means you won’t be left without hot water if your boiler ever suffers a breakdown.
Cons of heat-only boilers
There are some drawbacks to heat-only boilers, which you also need to consider:
Con: Heat-only boilers take up a lot of space
Out of the three types of boilers that are available, heat-only boilers take up the most space in your home.
In addition to the boiler itself; this setup requires space for a hot water cylinder, which is usually housed in an airing cupboard; plus room for two tanks in the loft (a cold water cistern and a feed and expansion tank).
This means that a heat-only boiler may not be suitable for flats or homes that have had a loft conversion.
Con: Heat-only boilers can temporarily run out of hot water
Since heat-only boilers store hot water to be used when needed; the amount of water that they can supply is limited by the capacity of your hot water cylinder.
After the water stored in the hot water cylinder is used up; you’ll need to wait for the boiler to heat up more water.
This potential problem can be minimised by choosing an expert engineer. They will recommend and install the correct size boiler and cylinder.
Con: Heat-only boilers are less efficient than other boiler types
Unfortunately, heat-only boilers are generally the least efficient type of boiler because they have the fewest control options.
They can also be less efficient because if you don’t use a lot of water. Because you may waste energy by heating a surplus in your cylinder. This doesn’t happen with a combi; which will only provide the amount of hot water you need.
If your hot water cylinder isn’t insulated, you’ll also be wasting lots of energy through heat loss. If you’ve ever noticed how warm an airing cupboard is, you’ve experienced heat loss from a hot water cylinder!
This problem can be reduced by fitting a hot water cylinder jacket . This reduces the rate of heat loss and keeps your water warmer for longer.
You might like our related blog: How to choose an energy efficient boiler.
Final thoughts…
Heat-only boilers are best suited to larger homes with multiple bathrooms; where several people all want to wash and shower at the same time.
Whilst you’ll need plenty of space to house the component parts; they’re a good choice for areas that suffer from low water pressure.
For tailored advice on which type of boiler would be best for your needs; contact one of our friendly team today.
