Sealed or vented?

[stevenmarston]

Sealed or Vented? We want to hire a plumber to install a new heating and plumbing in our home. It seems that before we can get proper quotes or make progress, we have to make a fundamental choice between using a sealed or a vented system. It’s a large house (six bedroom), and we’re a large family of two adults and four teenage children, and our highest priority of all relates to water pressure. It’s vital that we can at least have a system which allows us to be running three or four power showers, at the same time, and not have the water temperature or pressure affected if someone then turns on a tap or the dishwasher starts up etc. Right now, this doesn’t work at all with our current system, even with one shower on, if a tap goes on too then we’re either scalded or frozen, or both alternatively.

I know little of the two system choices, other than the snippets I’ve picked up from plumbers so far. I’m told the advantage of a sealed system is no water tanks or pipework in the attic (so nothing to freeze), less risks of leaks going un-noticed and less risk of air locks (especially in an old house like hours where pipes do tend to go up and down a lot to get around the layout of the house), but with the disadvantage that cold water is based on mains pressure and the hot water only works on pressure, no pump like a vented system would have, so the more taps/showers that are on, the lower the pressure and the more likelihood of temperature changes when taps are turned etc. I’m told the advantage of a vented system is that the water supply to the showers will be from stored water (hot and cold) in the tanks, so constant pressure to all showers until the tanks run dry and much less impact of taps being turned on etc, but the disadvantages are tanks and pipes in the attic that can freeze, leaks can go un-noticed as no drop in pressure and higher risk of air locks…

How on earth am I supposed to make this decision which way to go? I only know I want us all to be able to have a shower without being scaled or froze when the dishwasher starts or one of us stops our shower (and of course I’d prefer not to have frozen pipes, leaks and airlocks). Can anybody help me shine some light on this, how to make the decision, are there other things to be considered, are there ways around the disadvantages of either solution? We really need help here…

 

[grahamgas]

The most important thing is incoming flow rate.

You can measure this yourself. Fill a known volume ie a 5 litre bucket, and time how long it takes to fill.

This will give you your litre per minute flow rate.

If it is sufficient, then a Unvented hot water storage cylinder is what you want, coupled with a system boiler. Being a system boiler it is a sealed system and less likey to get problems later on.

The installer of the unvented also needs to be qualified to do so.

Take your measurements and let us know how you get on.

Wherabouts are you, someone on here may be local to you.

ps take it from a tap that uses main pressure.... easily mistaken sometimes.

hope this helps
Graham

 

[stevenmarston]

Addition: Some replies I got asked about our current cold water pressure. I did a test, using the kitchen tap which is about as close to the mains as possible, I'm getting 10 litres per minute, though it's much slower if I go to the upstairs bathroom taps, less than half that.

 

[PlumbBobBob]

the bathroom taps are probably fed from the cwst in the loft. an easy way to check is to put your thumb over the end of the cold and turn it on if you can stop the flow it is fed from above if it spurts out in is most likely mains fed.

 

[stevenmarston]

What do you think, is 10 litres per minute a sufficient mains pressure to use a sealed system, delivering sufficient cold water to 4 showers at the same time and still have a decent pressure and not major temperature changes when the dishwasher kicks in?

 

[PlumbBobBob]

10 litres per minute isn't the pressure it's the flow rate. you need to put a pressure tester on one of the first outlets on the system usually an outside tap to get an accurate pressure measurement.

 

[stevenmarston]

OK, will do - Can you give me any idea what you think would be workable pressure for a sealed system running a six bed house with four showers, two baths, kitchen and utility room? Where is the line between what can be done with a sealed system in terms of cold water pressure, and where it becomes necessary to use a vented system with cold water stores in the loft?

 

[Centralheatking]

I honestly consider it no contest given the size of your home and your requirements.

You need potentially large volumes of hot water (and cold) maybe at the same time.
In order to make sure this works at all times go for a conventional system with high
level cold water storage large dia pipes to deliver it - h & c. Mains cold to the kitchen
and mains cold supplies to all bathroom/ensuit basins - teethwashing and drinking.

Our place is 5 beds 3 w/c 2 showers and 1x with bath basins in every bedroom
with upto 6 of us here at max - say xmas. Plumbed like this 10 years ago
and it works.

Then look at the summer when your neighbour is hosing their garden all the time cause they are not on a meter and your water supply is a trickle. Come home from work and have a shower then !

Get a conventional system there will be plenty of advice as to which boiler is best

There is no theory here just solid practical advice based on sound plumbing experience
applied to my own home.

centralheatking

 

[stevenmarston]

Thanks for your detailed and really helpful response. I was wondering then, as you have this system, how did you deal with the disadvantages I'm told about, freezing pipes and tanks in the loft, air locks in the pipes and risk of leaks going un-noticed, any suggestions? Steve

 

[moony]

insulate and install correctly and you wont have problems.

i personally would consider upgrading mains and goin with the unvented.

 

[moony]

any plumber worth his salt should come around and do all this for you. and advise on the best system for your circumstances

 

[fuzzy]

unvented hot water and sealed heating, ie system boiler, no brainer for me

 

[Gray0689]

unvented hot water and sealed heating, ie system boiler, no brainer for me

Totally agree mate

 

[pauls]

system boiler and unvented wins hands down i personaly like this type of system.

 

[Dotty]

Aye. You can't beat belt and braces!

 

[Blackcatgas]

What do you think, is 10 litres per minute a sufficient mains pressure to use a sealed system, delivering sufficient cold water to 4 showers at the same time and still have a decent pressure and not major temperature changes when the dishwasher kicks in?

Not a chance in hell. Be honest, how many times does the situation arise where all four of you are having a shower?.

 

[BLOD]

I Agree with Blackcatgas

 

[oldplumber]

stick in at least one electric shower in your house, at least youll have the ability to wash when the boiler breaks down.

 

[Dannypipe]

The problem here is that there isnt a 'wrong' answer, just various opinions.

I'm fitting two boilers, linked in a very large house.This house is at least 6 bedrooms. It has 5 bathrooms. The system we're linking into was fitted ten years ago...by someone who was obviously very skilled and knowledgeable.

It is a open vented hotwater cylinder, with various flanges cut into it, supplying Stuart Turner pumps to all showers. The cylinder is huge. Then the central heating is a sealed system.

The pipework from the cold water storage tank is in 42mm, maybe bigger I'm going from memory here. Anyway, the system works very well. I was chatting to my work mate about the system and the total cost of all those pumps + the huge copper cylinder meant he could have just as easily had an unvented for less money. However we did realise that the demands on the house (at peak use) may exceed what an unvented can do. The jury is out.

We're bodering on light commercial so it would probably be advisable to speak to a plumber with experience in this field. Oh and if one of the boilers breaks down in the place I'm working on at the mo, then the other boiler could tick things over until it got sorted. We've linked a sequenser in for summer time to alternate the boilers and therefore lower fuel/service costs.

Who ever gets to do the job the OP is after is lucky. Jobs like this are what it's all about for me.