How JustAnswer Works:
  • Ask an Expert
    Experts are full of valuable knowledge and are ready to help with any question. Credentials confirmed by a Fortune 500 verification firm.
  • Get a Professional Answer
    Via email, text message, or notification as you wait on our site.
    Ask follow up questions if you need to.
  • 100% Satisfaction Guarantee
    Rate the answer you receive.
Ask Brian Your Own Question
Brian, HVAC Technician
Category: HVAC
Satisfied Customers: 827
Experience:  OFTEC registered oil heating engineer and plumber.
Type Your HVAC Question Here...
Brian is online now
A new question is answered every 9 seconds
This answer was rated:

what size boiler and tank do I need for 24 radiators and 3

showers and 1 bath? The... Show More
showers and 1 bath? The house is on 4 floors and 6 bedrooms and 3 bathrooms. If you could recommend a top of the range boiler and tank manufacturer I would appreciate this. Also would a closed loop boiler system work in a house of this size?
Thank you
Show Less
Ask Your Own HVAC Question

jrloar :

Hello, my name isXXXXX am looking forward to helping you solve your problem today. We need to know what size the rariators are, and the size of the house.


At present our plumber has put in 15mm pipe work in 2/3 floors and 1 ½ waste pipe running from all the bathrooms. We have asked that he does nothing further until we have had a discussion with an expert like yourself.


1.MAIN HOUSE - 4 storey house with 5/6 bedrooms and 3 bathrooms – 24 radiators and 3 towel rails

I attach the plans that our plumber has sent me and I believe the blue line is the 15mm pipeline he has already put in place on the first and second floor..

Please could you advise us on the following:


What size hot water tank is needed for a house this size? I think we talked about either a Heatrae Megflow ECO 3001 unvented Indirect Hot Water Cylinder or Heatre Megaflow ECO 300SF S28 unvented indirect sytemfit cylinder (which would you recommend?)


Which Gas boiler system would be best – I have looked at the Greenstar 40 CDi Regular Worcester boiler (again would you recommend something like this?)


There are 24 radiators and 3 towel rails what size copper pipe work would you recommend throughout the house to accommodate these, and pipe work to and from the boiler/tank?



2.GARDEN/BASEMENT FLAT – 2 bedrooms – 2 bathrooms (one en-suite) – including one bath and 2 showers, 2 towel rails and radiators throughout.


Which Gas boiler system would be best? I have looked at the Greenstar 30 CDi gas combi Worcester boiler (would you recommend something like this?)

What size copper pipe work is needed?


Hi Im Brian I can help you but lets take it one step at a time. I am looking at your origional question, and the size of the boiler will depend on the kw output you have on the radiators, I need to know what size radiators you have and if they are double or single. To work out the size of the cylinder I would like to know how many litres per minute your water supply gives you and what the total occupation of the property is ie how many people could live there. Definitely use a sealed or closed loop system. Domestic hot and cold water pipe work should be in 22mm from the rising main to the cylinder and all the way around the house it should reduce to 15mm as close to an outlet as possible, you will need to check your water pressure from the main is sufficient to cope with the demand, I would suggest you will need at least 2 bar but would prefer 3 bar. All the heating pipe work around the house should be 22mm spured off in 15mm to each radiator, you should have at least 2 heating zones one for living and one for sleeping, I personally would add another one for towel rads giving you the control to have heated towels when required without the need for your room radiators to be on. I would also consider using plastic pipe for the major part of the install. Your other property is easy. Yes a combi is perfect for the job, each to there own regarding boilers I like gloworm but hey ho there all guaranteed. 22mm pipework for the heating same spec as above, hot water feed will be in 15mm as that is what the boiler outlet is. Make sure the combi boiler has scale prevention device and put a Magna Clean on the heating system.

Customer reply replied 5 years ago.

I will check out the size of the radiators we are installing and get back to you shortly.

Thank you.


no problems

Related HVAC Questions