Is there a future for vented systems?

[sirocosm]

Coming from Canada, and having lived in Europe for some years, I was a bit surprised that people still install vented heating systems in the UK.

Does any other country still use vented systems? Either for heating or hot water?

Surely sealed systems are much better, especially since radiators are mostly made of mild steel?

 

[Madrab]

You'll be hard pushed to find a new domestic build with one these days.

Everyone now wants mains pressure hot water too.

 

[EFLImpudence]

Not being a 'heating engineer' but having done lots of 'plumbing', I have been wondering about this question.

Apart from the mains pressure at hot taps, and no need for cold water tank, which can be had with a combi, what are the advantages of an unvented system?

The need for specialist qualification to install is surely a disadvantage but perhaps not from your point of view.

Surely it makes no difference to the radiators, does it, or am I missing something?

 

[sirocosm]

Not being a 'heating engineer' but having done lots of 'plumbing', I have been wondering about this question.

Apart from the mains pressure at hot taps, and no need for cold water tank, which can be had with a combi, what are the advantages of an unvented system?

The need for specialist qualification to install is surely a disadvantage but perhaps not from your point of view.

Surely it makes no difference to the radiators, does it, or am I missing something?

For the heating system, the biggest drawback for an open vented system is corrosion, since the radiators are plain steel. Air can constantly get into the system from the F&E tank, so a sealed system prevents this.

For hot water I suppose an unvented system can give a better flow rate than a combi, especially if your boiler is small.

 

[EFLImpudence]

For the heating system, the biggest drawback for an open vented system is corrosion, since the radiators are plain steel. Air can constantly get into the system from the F&E tank, so a sealed system prevents this.

Ah, ok, I guess I wasn't thinking of combi as unvented, just G3.

However -

For hot water I suppose an unvented system can give a better flow rate than a combi, especially if your boiler is small.

now you seem to be doing the same.

 

[Madrab]

Apart from the mains pressure at hot taps, and no need for cold water tank, which can be had with a combi, what are the advantages of an unvented system?

Multiple outlets can be serviced at the same time with higher outputs and minimal drops in performance with larger amounts of stored hot water for multiple bathrooms. Siting of the cylinder can be varied, even in a garage. Space saving, as you mention, as no large cistern required. Economics - bit if contentious area as I believe the jury is still out on this one. If you have a large family that uses large amounts of hot water then heating a large cylinder of stored hot water can be more economical than a large combi running at full rate for extended periods of time.

 

[EFLImpudence]

Yes, as I have realised (although I think others do the same), I was thinking unvented only meant G3.

So, I suppose I actually agree with the OP in that an old-fashioned vented system would not be fitted today in preference to a combi-boiler which is, in fact, also an unvented system.

 

[Madrab]

That being said, some of the cleanest fault free systems I have come across are open vented. The usual problems are down to the valve motors failing. They are great low pressure (inherently safe) systems, even with their limitations, that require very little maintenance outwith the yearly checks for the boiler if set up properly.

 

[sirocosm]

That being said, some of the cleanest fault free systems I have come across are open vented. The usual problems are down to the valve motors failing. They are great low pressure (inherently safe) systems, even with their limitations, that require very little maintenance outwith the yearly checks for the boiler if set up properly.

I would have though that the radiators would rust, unless they are the old cast iron type.

 

[Madrab]

Not in my experience, a properly installed (leak free) and inhibited system will stay low in corrosion for years. Once the dissolved O2 in the water is displaced (one reason they use distilled water in parts of the EU) and isn't replaced then there's nothing to cause corrosion and as long as the system PH remains neutral then there's no galvanic action. Some of the cleanest I've found are old unvented systems.
Don't get me wrong, there's always some minimal magnetite at the bottom of the rads but you'll never get a system that's completely devoid of at least a little corrosion.

 

[Gasguru]

It's a complete fallacy to say sealed system don't corrode....some of the most corroded systems I've come across are sealed.
One of the dangers of a sealed system is owners leaving the filling loops connected and open....continual addition of fresh water is the quickest way to rot out a system.
It's also a myth that sealed systems don't get air in them....they certainly do if there's a leak on the system.

Only a quality installation with quality fittings etc will stay corrosion free.

 

[ReJect]

Sealed (unvented) heating systems have the advantage that they cannot flood a house if a leak developed - (say someone put a nail through a pipe) as only a small amount of water would take the pressure off the system.
Also a sealed heating system should not absorb and release air, whereas an open vent system does. Open vent systems also lose water to evaporation and therefore have to replenish water.

Unvented hot and cold water systems are much cheaper and quieter to run than a traditional open vented cylinder and cold tank with a quality pump.

But as above post said, open vent heating systems if done correctly and inhibitor added can be long lasting and fairly clean.
Also traditional open vented domestic water systems have been very reliable with almost no maintainence for decades and functioned well with taps suitable for gravity flow

 

[Gasguru]

I think you'll find that all those owners that have had their unvented cyclinders fail and not be covered by the warranty would disagree with you there
There's been a slow but increasing no. of Megaflo owners with failed baffles...new cylinder time.
The cost of a pump on an open vented cylinder is easily matched by routine costs of maintainence requirements...failed vessels, safety valves etc on an unvented.
You also run the risk that the local water undertaker will not maintain the higher pressure required and refuse to sort out flowrate issues...I've had customers with new cylinders with great flowrates/pressures down to 9litres/min after mains work in the road and their boundary stopcocks blocked. Only until you get to 8 litres/min will they investigate.

 

[Madrab]

One of the dangers of a sealed system is owners leaving the filling loops connected and open

I must say I'm seeing more of this where the mains has either been reduced to 1.5Bar @ the mains or on unvented that has the inlet set at 1.5bar and then some installers take the filling loop from there into the CH system and leave it open so it is 'in essence' self maintaining. That's until there is a leak and the mains happily feeds it with water until it's found

That and sealed systems are more liable to leakage due to the higher working pressures, one of the reason I always caveat a change to sealed if the customer doesn't want to upgrade the CH system, It'll be pressure tested but can't guarantee the longer term stability of the system fittings.

I'm a little confused ...... an open vented system won't absorb nor release air, nor will the water within the actual heating circuit evaporate. There will be a little at the header tank as they tend to be open topped but that's replenished by the valve. The actual system water, if there are no leaks (less likely long term due to it's low pressure), will require very little new water.

 

[sirocosm]

One of the dangers of a sealed system is owners leaving the filling loops connected and open....continual addition of fresh water is the quickest way to rot out a system.

In Canada they don't use filling loops any more, not sure they are even still legal. Systems are plumbed in directly to the mains with check valves and pressure reducers, and an isolation valve. I always kept mine closed since if it leaks and loses pressure I would want to know about it.

A well-sealed system should not corrode, although it will take a hit each time you have to refill it. The exchanger in the boiler I had in Canada was made of plain steel, not stainless. Wouldn't survive long in a vented system. That was some years ago and this has probably changed with the new condensing boilers, which corrode from the outside in.

It is also possible to use a plain steel tank for a thermal store if it is sealed, for example like this one, popular in Europe:
http://plumbingsupplies24.co.uk/hygienic-buffer-storage-tank-vertical/