Three main factors should determine your choice of a boiler. They are the fuel, the technology, and your existing plumbing.
Consider the last of these first. If you already have plumbing to a hot water storage tank in your loft, conventional boilers often make better sense. However, if you are starting from scratch, a combi is usually the cheapest to install, provided that it has sufficient heating power and water throughput for your home. Extensive re-plumbing and additional tanks can easily double the total cost of a boiler replacement, but if you already have a functional system, why waste it?
Fuel isn’t cheap, so your second consideration should be fuel economy. The options include electricity, mains gas, LPG bottled gas, oil (paraffin) and biomass. If you live off-the-grid, the last three are worth considering but for most urban home-owners electricity is the main alternative to gas boiler systems.
It is impossible to say whether gas or electricity will lead to the lowest long-term fuel bills. Both electricity and gas suppliers have a tendency to claim that they are the cheapest, but the relative price fluctuates and the cheapest today may not continue to be so in future years. Generally speaking, we would say that gas and gas boilers have been slightly cheaper in recent years, but against that is the fact that gas appliances require more maintenance. Whichever you choose, you are likely to save a lot more money by swapping your supplier than by swapping your fuel.
For off-grid properties, wood pellets are a cheaper fuel than oil or bottled gas, but always check the availability of fuel deliveries in your area, and the availability of qualified service engineers for that type of boiler.
Although you sometimes see boilers described as “condensing” boilers, you no longer need to worry about this term because EU legislation has obliged all manufacturers to switch to them. They are slightly more energy efficient than non-condensing boilers (in theory). However, if you already have an older non-condensing boiler, that is not a sufficient reason to scrap it. Many older boilers were better built and with a regular service could outlast a cheap modern replacement.
Combination boilers provide hot water for your taps and your central heating. They have some advantages but also some disadvantages. The disadvantages include a limited water throughput rate and the need for an external wall (because most are gas and require a flue). Many underpowered combis are fitted by landlords and homeowners trying to save a few pounds, but large baths and power showers can be rendered unusable when you replace a conventional boiler with a combi. In many cases, they fail to deliver an adequate supply in a building that has multiple taps and bathrooms. Additional pumps and hot water storage tanks can rectify most problems but that adds significantly to the cost.
The advantages of combi boilers are also numerous. Hot water is always available on demand – you don’t have to wait for it to heat up. Because combi boilers don’t require additional water storage tanks, plumbing them in is often less expensive. Lastly, because the water is only heated immediately before it is used, there is less energy wastage, so your bills may be lower.
Combis have been the most popular boiler choice in recent years but they are most suitable for smaller homes. Make sure you choose one with sufficient power.
Unlike the all-in-one combi, a conventional boiler system consists of a boiler, hot water cylinder, cold water storage cistern, expansion tank, plus a choice of control thermostats and timers. The cold-water storage and expansion tanks are usually located in your loft and the cylinder in a convenient cupboard (for example an airing cupboard).
The key advantage of this setup is that you have a good pre-heated supply of water when you need it, so you can fill a bath quickly and maintain a steady temperature (up to a certain volume determined by the cylinder size). If you have a gas-driven boiler you can add an additional electric immersion heater – giving you an alternative heating option.
Generally speaking, their greater capacity makes them a better solution for larger homes or buildings with multiple bathrooms. Unlike combis, when several taps are open at the same time, your water pressure and flow rates don’t decrease. They are also easy to link up with solar thermal panels.
Good insulation is important to get the best value from money, but the main reasons people replace them are to get higher water pressure or to get hot water on demand without having to preheat it. The several tanks used in these systems also take up a lot of space, so they are often removed during loft conversions.
A system boiler incorporates the feed water tank and expansion vessel into the boiler unit, otherwise they work much like a conventional boiler system, pre-filling the tank with hot water ready for use. Because they are virtually all-in-one, it is easier to install a system boiler than a complete conventional boiler system (assuming you don’t already have one of course). The lack of external tanks saves space and pipework (although not as much as a combi).
A key advantage of a system boiler is that the pre-heated water is connected directly to the mains and is delivered to your outlets at mains pressure. By contrast, conventional boilers rely on gravity to deliver the hot water to your taps from the loft tank, and the pressure can be quite low – especially on the upper floors.
If the internal tank in a system boiler is too small for your household’s needs, they can be linked up with additional storage tanks, but obviously this adds a cost and occupies some additional space.
All boiler types in the UK are available from leading boiler brands like Worcester-Bosch, Vaillant, Baxi, Glo-Worm, Potterton, Alpha and Intergas.
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