BOILERS

1. How do I know which type of boiler will suit my particular needs?

We strongly suggest that expert guidance be sought from a local accredited installer. He will be able to suggest the most appropriate type of boiler and advise of any upgrades to the system that may be necessary.

2. How do I know which size of boiler I will need?

Boiler selection should be based on a detailed survey of the property and a heat loss calculation. Once the energy requirement for the property has been established (expressed in kW or btu/hr), the model whose output most closely matches this requirement is selected.

3. Why do some of my radiators heat up more quickly than others?

It is likely that the system needs to be balanced. Your installer should be able to assist with this. Balancing involves setting the lockshield valve on each radiator to ¼ turn from fully closed then running the system from cold, noting the rate at which each radiator is heating up. The lockshield valve on any radiator, that is slow to heat up, should be opened slightly to encourage water flow to that radiator. Adjustments should be made until all radiators heat up at the same rate.

4. How do I get the most from my combination boiler?

In order to get the best from your combination boiler, it is important to understand the basic principles involved.
A combination boiler works on an “instantaneous” basis. Water drawn from the rising main to the tap is heated as it passes through the boiler’s domestic hot water calorifier. The temperature of water obtained is dependent on three factors: -

a)Boiler output
The performance of a boiler is directly related to it’s output (usually given in kW or Btu/hr)
b)Water flow rate
The speed at which water passes through the heat exchanger will determine how much heat is absorbed. A good analogy is a finger passing through a candle flame – whether the finger gets burnt or not depends on how quickly it is passed through the flame.
Boiler manufacturers will often quote a hot water flow rate for the appliance in l/min or gal/min. However, it is important when assessing the performance of a combi to remember that this flow rate is based on a specific temperature rise – usually 30˚C or 35˚C. If a greater temperature rise is required, the flow rate must be reduced. Conversely, a greater flow rate can be obtained if the temperature rise required is less.
e.g. A Combi with an output of 23kW gives a flow rate of 9.4 l/min for a temp rise of 35˚C but,
A flow rate of 8 l/min gives a temp rise of 41˚C
A flow rate of 10 l/min gives a temp rise of 33˚C
A flow rate of 15 l/min gives a temp rise of 22˚C

c)Incoming mains water temperature
We have already seen that the temperature rise depends on the flow rate, but the actual temperature obtained will depend on the initial mains water temperature. Because this varies, the apparent performance of the combi will change according to the season e.g. with the 23kW boiler, at standard water flow rate;
Summer- typical mains temp 15˚C, hot water temp 50˚C
Winter – typical mains temp 4˚C, hot water temp 39˚C

Note

The hot water produced by a combi is only available at one draw off point at any one time. Use of two points simultaneously will result in poor performance at both.

5. do the latest changes to the building regulations mean?

From 1 April 2005, Part L1 of the Building Regulations requires gas and oil boilers installed in new and existing dwellings to be condensing types, with a SEDBUK efficiency in band A or B, unless there are exceptional circumstances that make this impractical or too costly. In those cases where it is considered difficult to install a condensing boiler, an assessment procedure is used to demonstrate that a non-condensing boiler is justified.