Vented / Unvented systems

[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

 

[mickyg]

2 best options really are either fitting an unvented heated by the combi or uprating the boiler to a high flow model.

first job, measure your cold water flow rate. Bucket and stopwatch required.

 

[bengasman]

You are making the very common mistake of confusing flow and pressure.
Your boiler is a limited and cheap model, and often poorly installed as well. Chances are your water pressure is ok, but a flow limiter stops water going through the boiler at the rate you want.
Vented/unvented is one of the subjects that often leads to heated discussions.
I consider open vent systems hopelessly outdated and disgusting, others think they are the dog's whatsits as the tank will always top up and give a high flow. Pressure is useless unless you add a boosterpump. The worst part imho is the germ growth in unvented systems, and the dead flora and fauna that gets in there the moment it is not completely covered.

 

[phatz]

Thanks micky, sorry got more questions.
I heard it was easier to put in vented mains pressure system as there was no need for building regs and less maint etc. Why unvented - is it better for pressure?
What is a good mains pressure for this?
Have you got any recommendations for a flow combi?

 

[phatz]

Chances are your water pressure is ok, but a flow limiter stops water going through the boiler at the rate you want.
Vented/unvented is one of the subjects that often leads to heated discussions.
I consider open vent systems hopelessly outdated and disgusting, others think they are the dog's whatsits as the tank will always top up and give a high flow. Pressure is useless unless you add a boosterpump. The worst part imho is the germ growth in unvented systems, and the dead flora and fauna that gets in there the moment it is not completely covered.

ok so are you saying that its better to get a boiler that allows more through the flow limiter i.e. a system with a high flow rate. Aslo do you advise no mains pressure systems as vent systems are outdates and unvented systems get germ growth? Any advice on a combi boiler with a high flow rate? Apologies if getting muddled on this

 

[bengasman]

Sorry, my fault; mains = unvented, the tanks in the loft are vented systems.
Unvented systems are fine, only rather expensive to get a proper one that is correctly installed. As UNvented is mains, no germ growth.
Germ growth is the problem with vented (tank in loft).
The CDI series of Worcester Bosch are very good, and the big ones will run 2 normal showers without a problem, provided your incoming mains has enough flow and pressure.
The downside of UNvented is also that it depends on a proper incoming mains. The vented method is pretty much free of demands of incoming mains quality.

 

[mickyg]

firstly measure your cold water flow rate. This will define your options as it might not be as good as you think.
Time how long it takes to fill a given volume ie a 10litre bucket from your kitchen or garden tap and work out litres per minute.
For an unvented or high flow combi you ideally need 20 l/min+
If you have less than this then you will either have to go the vented route or rectify the pressure problem.

 

[phatz]

ok thanks for all the help, sorry for the delay - i did have to go to bed!. A couple more questions if I may.

I have seen something called a "Vented mains pressure" system. For example a company called Torrent do such a system.

Is this a better solution or is it best to stick with an unvented solution if this is the way i want to go?

Torrent Website
http://www.gasapplianceguide.co.uk/thermal_store.htm

Would this system still induce germ growth in this type of system per bengasman thread.

Cheers

 

[bengasman]

I don't do thermal stores, so am not an expert on them, but "vented mains" is a contradiction in terms; I suspect they came up with that to confuse buyers.
The company is gledhill by the way, not torrent.

 

[phatz]

Thanks bengasman. Will go and check them out and see what they say, will probably be posting back here in the near future. Thanks all for your help

bye

 

[GeorgeBramwell]

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

If your mains cannot be uprated then an accumulator is the best for you. Do a search on this forum. As you have decent combi, why not add a 24 or 28 killowatt combi, as that will save money, otherwise buy an ATAG 51KW or a large W-Bosch 42kW combi.

An unvented mains pressure system is a thermal store. There are advantages as it is not at high pressure and no yearly service charge. They work well.

 

[mickyg]

oh dear, dr drivel back again
how can you recommend an accumulator when you have no idea what the standing pressure is?
Are you recommending an "additonal" combi? when you have no idea of the hot water demand or size of the house?
How long before you come back as one of your many other disguises?
Funny how now you pretend to be an installer when you've always showed such discontempt for them.

 

[GeorgeBramwell]

discontempt

That is a good one. I have never heard that before. What does it mean?

If he needs more DHW flow then an additional combi is the cheapest way as he already has a good one. He can spend £600-700 on an additional combi or £2K on a high flow model. I know what I would rather spend my money on. The new combi can be rigged up to do a CH zone. An accumulator installation is cheaper than a low pressure cylinder and and a tank in the loft. That is a lot of labour to do and then he needs a power shower pump as well. Assuming he has decent static pressure of course. An accumulator is childs play to connect and take a no time at all.

 

[bengasman]

...If he needs more DHW flow then an additional combi is the cheapest way as he already has a good one. He can spend £600-700 on an additional combi ...

I think you just proved you have no idea about the how and what of boilers. The cheapest of the cheap combi with all the bits and pieces needed to fit it legally, and connect it up will give you very little change from 600 quid; you are clearly not a RGI.

 

[GeorgeBramwell]

...If he needs more DHW flow then an additional combi is the cheapest way as he already has a good one. He can spend £600-700 on an additional combi ...

I think you just proved you have no idea about the how and what of boilers.

Do you mean I do not know what a combi is?

The cheapest of the cheap combi with all the bits and pieces needed to fit it legally, and connect it up will give you very little change from 600 quid; you are clearly not a RGI.

I wrote £600-700. You put that in bold.