Vented / Unvented Mains pressure system

[phatz]

Hi,

Apologies if this is the wrong area, please redirect me to where I should post this if needs be. I have a number of questions around mains pressure systems.

We have moved in to a house which runs a worcester bosh junior combi boiler with no gravity fed system. The hotwater pressure is quite poor i.e. when two hot water taps are run the pressure drops from the boiler basically I think that the pressure from the boiler when two hotwater taps are running is poor even though our mains pressure is good (probably wrong size boiler for the job).

I have been looking at the possibilities of a Vented / Unvented Mains Pressure system for the hotwater instead, as we have no gravity system (so no pumps for power showers can be installed) and would like to have someone running a bath and someone washing up with no hotwater pressure drop.

1. Which is better? Vented or unvented mains Pressure systems or increase size of combi?
2. Where can vented /unvented systems be installed? Attic, Loft Space, Ground flooor level etc etc?
3. Can a combi boiler heat the Vented, Unvented mains pressure system?


Any ideas greatly appreciated.

Thanks again

Phatz

 

[Mike Jackson]

Provided you've got the flow and pressure available unvented is better. An unvented cylinder can be sited anywhere but be aware of the need for the safety discharge pipework, the longer the run the larger it needs to be. Unvented cylinders need to be installed by someone with the correct certificate of competence.

You can use a combi like a system boiler by adding two zone valves. You can also leave the hot water to one outlet running from the combi and run the rest from a cylinder. This is quite a common fix where a combi has been underspeced.

 

[phatz]

Thanks for this Mike, as a novice what kind of flowrate and pressure is classed as good for this kind of system. Also is getting building regs approved for unvented systems straight forward, I was initially thinking of vented mains pressure systems as they are reported to be easier to install and maintain?

 

[Mike Jackson]

By vented mains pressure I take it you are thinking of a thermal store. As far as I am concerned they are the work of the devil, nasty things suited to collecting sludge and destroying the system. Also most thermal stores are not suited to your boiler, you would need a twin coil set up.

You don't need to get building regs approval for an unvented as long as it's installed by an approved installer who will notify the installation.

For an unventyed to work well you need a minimum of 1 bar (preferably more) dynamic and at least 20 l/min. I would be looking for 30 l/min before installing an unvented.