Considering the pro cans cons of moving form an open vented central heating & hot water system to a sealed pressurised system

One question I have do you still need to balance radiators in a sealed system or not ?


nothing changes in heating between the 2 systems

  • To clarify is this understanding correct, what does happen is the water in the central heating system part is filled up from the pressurised mains water, then sealed so no water lost and therefore no cold water top up needed and hence less energy needed because not heating up fresh water only previously fresh water. But what I dont understand is having the water under mains pressure mean that it travels round the ch heating system easier, and is a pump still required ? – Paul Taylor Dec 5 '17 at 12:35
  • Systems were installed many years ago that did not need circulating pumps. The system piping was much larger to allow for a gravity flow system. The downside was a system that responded very slowly to temperature changes, both hotter and colder due to the slow movement of the water, and greatly increased fuel cost. As for a sealed system or an open expansion tank in the loft, both systems should operate the exactly the same. Water is held up to the highest radiator by the water pressure. The sealed tank can be mounted anywhere in the system. and the other must be above all radiators – d.george Dec 9 '17 at 16:21
  • But isnt the water pressure much higer in a sealed system, therefore more effective at getting water to radaitors higher up ? – Paul Taylor Dec 9 '17 at 19:09
  • The amount of pressure in the system has nothing to do with the performance of the system, and is only there to insure that the water in the system is being held up to a point above the highest radiator. Whether the system has a sealed expansion tank or an open expansion tank mounted above the highest radiator has nothing to do with the systems operation and both are there to give the expanded water somewhere to go. Remember that when water is heated it expands, and either tank is a reservoir for that expanded water. – d.george Dec 11 '17 at 10:39
  • I needed more room. So 1 pound of gauge pressure will hold a column of water up above the gauge 2.31 feet.10 pounds of pressure will hold the same column of water up 23.1 feet and so on.. If the top of the highest radiator in your system is was 40 feet above the pressure gauge then you would need about 17.3 pounds pressure to keep the water above the top of that radiator (40 divided by 2.31 + 17.3) pounds pressure and add 2-3 pounds for safety. That is how the pressure is used in the system. Higher or lower pressure has no affect on system performance, it just holds the water up. – d.george Dec 11 '17 at 10:52

Yes, you still need to balance radiators in a sealed system.

Radiator balancing is to do with controlling the flow. Whatever the "at-rest" pressure is, the pump adds pressure to the flow pipes and reduces it in the return pipes.

The flow of water to each radiator is controlled by the ratio of pressure/losses compared to other radiators, not compared to the overall pressure.


Yes, but in a closed system you can add 'automatic' balancing valves (requires at least 1.5 mwc of head) like Caleffi's Dynamical where the only thing you have to know is the maximum flow required, set the requuired flow on the 'internal' dial and your system is balanced without mthe effort needed on traditional systems. You cannot usually do this in an open system as head is not enough.

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