There are many different ways to generate hot water for your home, but which one best suits your individual needs?
Take a look at the pros and cons for:
(MORE: hot water storage)
Widely used in flats and starter homes, the combination boiler provides instantaneous hot water, as well as supplying hot water for space heating.
They are cheap and quick to install. They are also space-efficient as there is no need for a hot water cylinder or feed and expansion tank in the loft.
The hot water flow rates are not great and they don’t cope well if you want more than one hot tap open at a time. They are also not terribly efficient, as the boiler size needed to provide instant hot water is larger than that needed to provide space heating.
Cost: Around £1,000.
More like the ‘regular’ arrangement, with the hot water stored in a separate tank, though nowadays usually under mains pressure (the system is sealed), thus negating the need for a feed and expansion tank in the loft.
The overall performance is better than a combi’s as it can satisfy a higher heat demand, and as all of the main components are built in (i.e. expansion vessel and pump) the installation is quick and neat.
Will run out of hot water if overused. Some installers claim that they are more prone to problems such as pressure loss.
Cost: Around £1,000.
Heat pumps extract heat from the outside ground or air for use in space or water heating. They work best with large storage tanks which don’t need to be heated to such high temperatures.
Can work in temperatures as low as -15°C and require little maintenance.
While efficient at delivering hot water at lower temperatures, typically around 45°C, making them ideal for underfloor heating, hot water needs to be a lot warmer than this (minimum 55°C, sometimes 70°C), and here the technology struggles.
Cost: From £6,000 for air; £9,000 for ground.
The final fallback, when all else fails, is the electric immersion heater, which is a simple element not unlike an electric kettle, which fits into the top of a hot water tank.
It’s very cheap and, if it’s run off Economy 7 tariffs, it’s no more expensive to operate than an oil-fired boiler.
It’s still more expensive than gas for which it is often installed as a back-up supply.
Cost: From around £20.
There is a small but growing interest in biomass boilers, principally fired with wood chip or wood pellets. These are widely used in Austria and Scandinavia and are available with features such as automatic ignition and auto-feed mechanisms — the push-button convenience normally associated with gas or oil. However, they need space to operate in and for fuel storage.
(MORE: Guide to Biomass Boilers)
The oldest of the renewable technologies, the solar panel is designed to provide domestic hot water when the sun shines. The size and number of the panels you need should correlate to the number of people in the house (and hence the hot water demand). A well-designed solar panel system should provide most of your hot water during the summer and the shoulder seasons, conceivably halving your domestic hot water bills.
(MORE: Guide to Solar Panels)
What’s Wrong With ‘Regular’ Boilers?
Regular, or ‘conventional’, boilers are now largely bought as replacements for homes with an open-vented heating system (i.e. supplied by a feed and expansion tank in the roof space, meaning the system is open to air). Like system boilers (which run on more efficient sealed circuits, pressurised to 1 bar), they work on the principle of stored water and require a separate cylinder. However, they’re more expensive to install, needing extra components and pipework, and also take up more space. They can also suffer from low pressure if the feed and expansion tank is not located high enough, meaning additional shower boosters may be required; yet this is the ideal setup for a ‘power’ shower, which requires a cold water feed from the cistern and a separate electric pump.
Integrating your hot water system
If you are considering using a variety of heat sources, such as solar thermal panels, heat pumps and woodburning stoves, you will want to integrate these with a hot water delivery system. The solution is a large tank capable of taking on a number of heat sources.
It’s a specialist area and it pays to use a specialist designer and a knowledgeable installer. Two self build businesses specialising in this area are Chelmer Heating and Nu Heat. Alternatively, look out for a new range of heat pumps, the Genvex Combi, which delivers hot water combined with mechanical ventilation with heat recovery (MVHR).
Sizing Hot Water Cylinders
How much hot water do you need to store? Modern tanks are well insulated and will hang onto their heat for two days or more, so in some ways it makes sense to have as large a tank as possible as the water acts as an energy battery, especially if you are using renewable heat sources such as solar panels.
Typical cylinder sizes for four bedroom homes are 140 or 175 litres, but there are many options above 200 litres. Some eco homes base their entire heating strategy around storing huge amounts of hot water (500 litres, sometimes even 1,000), but these huge tanks are bulky and heavy and ideally need housing in a utility area or basement.
Making the Decision
Most self builders will opt for a gas-fired system boiler – making the system size and efficiency the most important considerations – but small homes can justify a combi boiler. If building off-mains or installing renewables, the decision is not so simple. Homes with enough space are well suited to a ground-source heat pump for space heating with perhaps solar thermal panels backed up by an immersion heater for hot water.
Note Ratings Changed: The way in which boilers are rated by SEDBUK has changed. Previously graded from A to G, they are now rated by their efficiency as a percentage. Aim for as close to 90% as possible.