The Law of Entropy

The Law of Entropy states that:

Energy In₁ = Energy Out₂ + Losses_z

Thus, if you put 100 units in, you will always get 100 units out. Any boiler putting 100 units of energy (gas, oil, LPG), in will get the same out, but the ‘mix’ between Energy Out₂ and Losses_z will vary with each application:

If your existing boiler is ‘open-flued’ that is, with a pipe coming off the top of the boiler into a flue or chimney, switch to a balanced flue appliance. Open flue is the least efficient alternative available, and should be considered only where dictated by the specific boiler location.

Entropic Factor: 100 _IN = 68 _OUT + 32 _LOSSES

A ‘balanced flue’ appliance takes the flue (usually fan assisted) directly through an outside wall, two pipes, a smaller one inside a larger one, draw in fresh air for combustion from one of the pipes, and exhaust the products of that combustion through the other pipe.

Balanced flue boilers are more economical to run than open flue boilers, they are higher efficiency (around 78%), and much safer than an open-flue, as the flue is sealed from the room in which the boiler is installed.

Entropic Factor: 100 _IN = 78 _OUT + 22 _LOSSES

Having settled upon a balanced flue appliance, the next decision might be to consider if you require the cheapest, safe alternative open to you, in which case there are a wide range of boilers you could consider. If however, you are interested in reducing emissions into the environment and making further fuel cost savings compared to an everyday balanced flue boiler, you might consider a fully ‘condensing’ boiler, which offers at least 92% efficiency.

A ‘condensing boiler’ offers the most advanced approach thus far developed for the minimisation of losses referred to above in the law of Entropy. With a standard boiler, the fuel is burned in the boiler chamber (heat exchanger) and passed across water which is heated, the exhaust is then passed to outside atmosphere through the flue. With a condensing boiler however, the exhaust is then passed across a second chamber (or the same chamber twice on some boilers) to collect more of the heat ‘missed’ during the first pass across the heat exchanger, thus considerably improved boiler efficiency.

This additional technology does not come without cost, and typically adds approximately £300 to the cost of the boiler.

Entropic Factor: 100 _IN = 92 _OUT + 8 _LOSSES

‘Combination boilers’ allow for much reduced installation time and therefore cost as the heating and hot water functions are ‘combined’ within the case of the boiler. There is no need for an airing cupboard with a hot water cylinder inside, or a ‘header’ tank in the loft.

However, combination boilers offer their own issues which may or may not affect your decision. Combination boilers have a separate (small) heating unit/system for the hot water, this has a flow rate restricted by the incoming property mains water pressure, and the maximum flow rate out of the boiler. This means hot water to the bath will not flow at anything like the rate you may be accustomed to with a traditional system, incorporating a cylinder. If you are a household who only partake of showers this may be less of a concern. Because there are no tanks involved, the boiler delivers hot water at mains pressure. If you have older taps in your home, they may not be able to withstand mains pressure supply, and begin to leak, leading to replacement, or problems with the boiler (it gets confused if hot water is called for at a very low rate i.e. a drip).

Combination boilers are popular with small property developers because of their compactness and popular with some installers as they are quick and easy to fit. They are however, complex to maintain and not all Service Engineers will be prepared to work on them. These boilers need specialist routine maintenance to ensure proper operation, failure to do this can significantly reduce the life expectancy of the boiler.

The most appropriate location for a combination boiler is a 1 or 2 bedrooms flat or apartment, if you enjoy 3 hours in the bath with a good book and a large gin and tonic, avoid these systems.

Life expectancy for a domestic boiler is 12+ years, it should be born in mind that a heating system pumps water through a series of steel/iron radiators, water combines with iron very efficiently to create – rust. When contemplating a boiler replacement, it is of paramount importance that the existing system is emptied of water and then ‘power-flushed’ clean using cleaning chemicals. Once the new boiler has been installed, the system should be refilled with clean water which has its acidity neutralised and inhibitors installed to prevent further corrosion.

Failure to undertake this preventative maintenance could result in boiler failure within 18 months of installation, some boiler manufacturers will not honour their guarantees if the system was not ‘power-flushed’ as part of the installation. This is a very time consuming task (not less than half a days work) and therefore can get overlooked by the more casual installer, and is an expensive but vital addition to the cost of boiler replacement. Typically, a ‘power-flush’ will cost between £400 - £900 depending upon system size.

Need more hot water?

If the boiler replacement is part of other works, such as an extension to your home, or a new kitchen/bathroom, it may well be the appropriate time to upgrade the hot water system. Perhaps a growing family or larger bathtub(s) cause the old system to struggle with the hot water demand; there are several alternatives for increasing hot water capacity.

In the case of an extension, the new loft space may well allow the installation of a second hot water cylinder. If your home has reasonable cold mains supply pressure you might consider a mains fed cylinder which is heated by off-peak electricity and can be sized to meet any amount of hot water demand at a very competitive cost. This type of system provides excellent pressure at the tap or shower head and requires only limited maintenance.

If the increased demand is more modest, the existing airing cupboard may have room for a larger capacity cylinder. They come taller as well as fatter, so you may lose a few centimetres of airing space but gain the extra hot water your growing family demands.

The installation of a larger capacity pressurised hot water cylinder would effectively alleviate the hot water provision from the boiler, as the water is heated by electricity, and may allow a smaller sized boiler to be installed, to satisfy the heating demand, lowering the cost of installation.

You should not attempt to solve a hot water demand problem with any make or model of ‘combination’ boiler; they have very limited capacity for hot water supply (which is often exaggerated by the manufacturers) and have very specific applications where their installation is appropriate, such as small flats/apartments for 1 or 2 people who prefer showers to baths.