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Choosing a new boiler? Hot Water Storage Vessel / Mega Flow or Combi?


If you're trying to choose a new boiler, which is the best for you? A hot water storage vessel, a Mega flow or a Combination boiler? It’s all about meeting your hot water demands, having adequate space and trying to save money on fuel bills! Let's explore your options..


Unvented Hot Water Storage Vessel or Mega Flow


If you are likely to have more than 1 bathroom in use at once, such as a large family home with more than 3 bathrooms, then you'll need a Mega flow or an unvented hot water storage vessel.


They come in all different sizes. Some can be connected to solar panels and used as an energy saver. Others can work off the electric and don’t need to be connected to a gas boiler, which can be quite costly to run.


A "Mega Flow" can connect with a gas boiler, which is a manufacturer name for an unvented hot water vessel. These are connected straight to the incoming water mains which gives you a high pressure supply of hot water.



Hot Water Storage Vessel or Mega Flow - For:


  • Lots of stored hot water
  • High pressure and volume of hot water up to 25 litres a minute                                        
  • Can run up to 3 baths at the same time
  • No need for booster pumps for showers and baths
  • No need for cold water storage tanks as all off the mains water
  • Can use solar panels to heat water to reduce fuel costs
  • Can be installed when there is no gas supply to property
  • Electrical heat back up if boiler breaks down


Hot Water Storage Vessel or Mega Flow - Against:


  • Will take up storage space
  • Very heavy and bulky
  • More electrical and mechanical controls to breakdown
  • Will take about 45 minutes to recover when all the stored hot water is used up
  • Less energy efficient to run than a combination boiler if connected to electric only
  • You need a minimum flow rate of 16 litres of water from your water main with a minimum of 1 bar operating pressure on a 22mm diameter cold water main pipe
  • Large sized water supply
  • More maintenance as the unvented storage vessel and the boiler will have to be serviced every year
  • You need to heat the whole storage vessel even if you only use a basin of hot water


The Combination Boiler




Combination Boiler - For:


  • Takes up very little space
  • Doesn’t need much water pressure to operate only 0.7 bar. Or 7 litres a minute
  • Instant hot water when you need it only 20 seconds heat up time
  • You can have as little or as much as you wish of hot water as you like
  • Very energy efficient as haven’t got to heat big storage vessel
  • Half the cost of an unvented cylinder and boiler installation
  • Cheaper to maintain and service
  • Perfect for smaller properties like 3 bedroom and under
  • No risk of legionella
  • Can run on oil, gas, electric and LPG
  • Fast installation
  • Less electrical and mechanical controls to breakdown


Combination Boiler - Against:


  • Can only run 1 bath at a time
  • Will not cope with more than 2 bathrooms working at one time
  • May require bigger gas supply
  • Needs gas to property
  • Can only deliver a maximum of 16 litres a minute of hot water
  • not suitable for large properties with more than 2 bathrooms


If you need more help choosing, call us on 0800 3280449 - we'd love to hear from you!


Alternatively submit your enquiry via our Contact us page, find out more about us or find out potential costs with a fast quote.


Author: Tony Hernandez



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