What boiler do I need?

Posted April 2, 2019 by Jon Matthews

It can be a daunting when faced with changing or upgrading your boiler as there are many on options in terms of type and size. You will need to consider what is best for your property and also your personal requirements. Heating systems are not a cheap purchase and unless you get it right, you could spend a lot of money on a system that does not meet your requirements/expectations or spending too much on system that will deliver no additional benefits than that of a cheaper option. It is vital that you employ an experienced engineer to help you make your choice. Unfortunately, being Gas Safe registered is not a guarantee of heating system knowledge. As well as the Gas Safe regulations you must also comply with parts L and G of the building regulations.

So, what do you need to consider?

  • What size do I need to heat your home, office etc? This will be calculated from the heat loss of the property. Size of the property and insulation levels will determine this figure. So, for example a 4 bedroom detached built in 2000 with insulated walls and double glazing will have a much lower heat loss than a similar sized 4 bedroom property built in 1900 with solid walls and single glazed sash windows. Therefore, the property built in 2000 will need a much smaller boiler. A common mistake is to go off the number of radiators in the property. Both examples above could have the same number of radiators, but the property built in 1900 could need a boiler twice the size as the 2000 built property.
  • The next key piece of information required is what are your hot water requirements. This will normally be determined by the number of hot water outlets e.g. number of bathrooms, showers, sinks etc. Consideration also needs to be given to how usage can be affected by external influences such as the number of household occupants or type of use such as sinks in a restaurant or bathing facilities in an elderly care home. At this stage the incoming water main needs to be checked to see if there is enough flow and pressure to meet these requirements. This is very important when you are considering a combi boiler or a mains pressure unvented cylinder. For example, if you wanted really good shower pressure and chose a combi boiler that could deliver 20 litres per minute (l/m) and your water main was only delivering 12 l/m, the boiler would only heat 12 l/m meaning you would have wasted hundreds of pounds on a boiler that is too big.
  • Using the information obtained in points 1 and 2 you can then decide what type of system you want and more importantly what will work.
    1. Combi Boiler – Most modern combi boilers would be suitable for up to a 4-5 bed property with a bathroom and an en-suite and will provide heating and hot water on demand. Benefits are you only heat the water you use, and all the main components of a heating system are in the boiler and are covered by a 10 year guarantee. Downsides are they are not suitable for larger properties and in the event of failure you have not back up for the hot water.
    2. System Boiler + Unvented Cylinder – Typically suited to larger properties 4-5 Bed + with 2 bathrooms or more. Great hot water flow rates, hot water back up via immersion heater on the cylinder. Downsides are you need more room to house a cylinder. More expensive.
    3. Regular Boiler – Typically for use on low pressure systems with a gravity fed hot water cylinder. These should be considered if looking for a cheaper alternative (like for like) or if the central heating system is old and fragile and pressurising it with a system or combi boiler could cause potential issues and further cost. Benefits are they are relatively cheap to install. Downside is poor hot water flow rates.