Unvented or Vented Cylinder - Which do i go for?

[rossyl]

Hi,

I am after some of your worldy advice. I had asked a similar question re combi or cylinder, and have decided on cylinder but I am now seeking a bit more knowledge on venter or unvented and any other types that exist.

Firstly, I am not installing anything, I will be getting professionals in. A lot of pipework will be being replaced, as it will be part of a considerable house renovation. It is possible that the supply may be changed, if the current supply is lead. The house is a mid-terrace property at the bottom of a hill, at the top of the hill sits a large resevoir that I presume must be the supply. I am yet to check the flow rate as I only complete on the purchase of the house next week.

I was wondering if a system boiler with an unvented cylinder is the best way to go, or are there other items on the market such as vented cylinders that would be a better idea.

My biggest concern is ensuring that I can have two bathrooms and a kitchen tap all running at the same time and that there will be sufficient hot water and pressure in that water.

It's a mid-terrace property. Boiler will be on the ground floor. There will be a downstairs loo, a 1st floor family bathroom, a 2nd floor ensuite bathroom.

I am aware that unvented cylinders are more complex to install and require certifications, that is not really of much concern as I intend to be getting the relevantly qualified people.

Thanks very much
Ross

 

[McCombi]

If the mains water pressure is adequate coming into the house then unvented would be my first choice due to the quick heat recovery times and the pressure going to the taps. Find out what the pressure is like entering the property and compare it to the spec of the cylinder you want before purchasing anything. If the pressure isn't high enough it won't do the job correctly.

 

[mysteryman]

You need good pressure and flowrate. An old lead incoming mains pipe should be replaced anyway.

 

[rossyl]

If the mains water pressure is adequate coming into the house then unvented would be my first choice due to the quick heat recovery times and the pressure going to the taps. Find out what the pressure is like entering the property and compare it to the spec of the cylinder you want before purchasing anything. If the pressure isn't high enough it won't do the job correctly.

Thanks very much. I did not realise that Vented required a higher pressure/flow than Unvented

 

[45yearsagasman]

two bathrooms and a kitchen tap all running at the same time

 

[SimonH2]

I did not realise that Vented required a higher pressure/flow than Unvented

An unvented cylinder has a header tank above it (usually in the loft). Your mains flow rate & pressure are (almost) immaterial since the water you use comes from the header tank. The mains flow refills the header tank via a ballcock.
If you have poor mains flow rate, then you'll need a larger header tank as it won't refill as much during use. As long as the flow rate isn't too low, then the header tank can take it's time to refill.
So your flow rate at the tape is determined only by the pipe size/length and height of the header tank above the tap.

For an unvented cylinder, it's connected directly* to the mains with no storage. So every drop of water you draw off needs to be replaced by water from the mains. Thus you can't get water out of the taps faster than it can come from the mains.
On the upside, the pressure is higher as long as your mains can supply it.
It is possible to add some accumulators which will give a short term improvement to flow rates.

* Directly actually means via some safety valving which limits pressure and in the cylinder.