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Frequently Asked Questions
Q:- "How do I know which type of boiler will suit my particular needs?"
A:- 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.
Q:- "Why does my heating system not produce the needed amount of heat?"
A:- Check the thermostat and adjust to the desired temperature.
Q:- "How do I know which size of boiler I will need?"
A:- 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.
Q:- "Why do some of my radiators heat up more quickly than others?"
A:- 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.
Q:- "How do I get the most from my combination boiler?"
A:- 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.
Q:- "What do the changes to the building regulations mean?"
A:- From 1 April 2005, Part L1 of the Building Regulations requires gas 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.
Q:- "What is SEDBUK rating?"
A:- The SEDBUK (Seasonal Efficiency of Domestic Boilers in the UK) rating is the average annual efficiency achieved in typical domestic conditions and is quoted in a series of bands (from ‘A’ at 90% to ‘G’ at below 70%). So SEDBUK ‘A’ boilers are the most efficient.
Q:- "How do condensing boilers work?"
A:- Condensing boilers work on the principal of recovering as much as possible of the waste heat that is normally rejected into the atmosphere from the flue of standard efficiency (non-condensing) boiler. This is achieved by using an extra-large heat exchanger (or sometimes two heat exchangers) within the boiler. This maximises heat transfer from the burner as well as recovering useful heat that would normally be lost with the flue gases. When in condensing mode the flue gases give up their latent heat that is then recovered by the heat exchanger within the boiler.
As a result the temperature o the gases from the flue of a condensing boiler is typically 50-60C compared with 120-180C in a current non-condensing boiler. If your boiler is working properly you should see a plume of vapour from the flue. At the same time an amount of water or condensate is produced within the boiler and has to be plumbed to a convenient drain point.
Q:- "How do condensing boilers work?"
A:- Condensing boilers work on the principal of recovering as much as possible of the waste heat that is normally rejected into the atmosphere from the flue of standard efficiency (non-condensing) boiler. This is achieved by using an extra-large heat exchanger (or sometimes two heat exchangers) within the boiler. This maximises heat transfer from the burner as well as recovering useful heat that would normally be lost with the flue gases. When in condensing mode the flue gases give up their latent heat that is then recovered by the heat exchanger within the boiler.
Q:- "Are condensing boilers more expensive to buy and install?"
A:- The extra cost is usually limited. A condensing boiler normally costs more to buy because it uses more expensive materials for the heat exchanger. Often the difference can be offset by grants from Energy Supply Companies, or local authorities, or via Energy Efficiency Advice Centres (EEAC’s). Installation will incur an extra cost as a result of fitting a condense drain, but this is usually a simple plumbing job. There may be flueing costs to ensure the plume does not cause a nuisance. Glow-worm offers a unique Plume Management Kit to solve this problem.
Q:- "Can condensing boilers be fitted to existing systems?"
A:- Yes. Condensing boilers are suitable for replacing most existing boilers. However, because there are currently no condensing back boilers or heating-only floor standing boilers, they are likely to require boiler relocation. Controls are another consideration. Existing older systems may use gravity hot water circulation. This is much less efficient than pumped hot water. Condensing boilers only work on pumped hot water, so a system upgrade will be required in this case. As with every boiler replacement, cleaning and flushing the system before fitting a new boiler is very important to ensure it works reliably and efficiently.
Q:- "Are condensing boilers more difficult to service and maintain?"
A:- Not significantly. The annual service should include checking that the condensate drain is clear, but this only takes a few minutes to complete.
Q:- "Do they need to run in condensing mode all the time to be more efficient?"
A:- No. Due to its larger heat exchanger, a condensing boiler does not have to condense in order to be more efficient. Typically a new gas-condensing boiler will have a seasonal efficiency of between 84% and 92% compared with a new non-condensing boiler at 78% or an older boiler at 55-65%.
Q:- "Do they need larger radiators to be fitted?"
A:- No. In most systems, radiators are already oversized for all but the severest weather. A marginal benefit of approximately 3% may be obtained from over sizing radiators for a new system, as this will allows slightly cooler return water to the boiler and maximize time spent in condensing mode. For existing systems, it is nearly always uneconomic and unnecessary.
Q:- "Do I need to find a specialist installer?"
A:- No. As you would expect from the previous answers, condensing boilers require the same skills to fit as standard boilers. Glow-worm support this with a large investment in high quality installer training. There is also a recognized qualification for installers called ‘Certificate in Energy Efficiency for Domestic Heating’, that relates solely to condensing boilers.
Q:- "What is pluming?"
A:- Because the flue gases leaving a condensing boiler are cool, they normally produce a visible mist or plume of water vapour around the flue terminal itself. This is because the gases condense on contact with the outside air. It will be more noticeable under cold conditions, when even standard efficiency boilers can plume as well. This is not a problem and in fact indicates that the boiler is working efficiently. However, consideration should be given to boiler and flue location prior to installation so that the plume will not be too close to neighbouring properties or to windows, doors and paths regularly used in the winter.
Q:- "Are they less reliable than standard efficiency boilers?"
A:- No. Any faults that occur are generally nothing to do with their condensing features. Glow-worm has built an exceptional track record for condensing reliability with very demanding specifiers based on 3rd generation designs and high quality manufacturing facilities.
Q:- "When do installers need to obtain their Certificate in Energy Efficiency for Domestic Heating Qualification?"
A:- Many people within the heating industry think that the Certificate in Energy Efficiency for Domestic Heating accreditation will be required for April 2005 onwards. In fact, it is April 2006.
When CORGI sends renewal of registration notices to installers in January, installers can also tick a box saying they want to register on the ‘Competent Person’s Scheme’ to self-certify from April 2005. For Part L compliance of the new Building Regulations, Certificate in Energy Efficiency for Domestic Heating accreditation is required to demonstrate competence, but installers have up to a year to complete it.
Info from Glow-worm
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