To vent or unvent, that is the question?

[Andrew Johnson]

Hi. We have moved to a new house with 3 bathrooms and need to move the hot water tank due to some interior work on the upstairs. We currently have a vented system, and so we are considering changing to an unvented system. As part of this we are going to also get a new boiler and flush the system.

I had heard of unvented systems, which would get rid of the large water tanks in the attic which certainly appealed to me. But with one of the issues being pressure living on a hill. We have been told we have 1.5bar by the water board and I have read this is the minimum required.

So my questions are

1. Will that pressure be enough for an unvented system? 2 plumbers have been around and felt it would be ok noting the flow being the key, and seeing the pipe coming into the house felt we would be ok. What are people’s views on this forum?

2. What are the benefits of moving to an unvented system? Are they more reliable? Less maintenance? Last longer? More efficient?

3. We live in a high chalk area, and had a passing comment from a neighbour that that would cause issues with an unvented (something about in a vented hot water tank the chalk drops to the bottom and won’t feed into the system). Is this right?

Anyway, all advice and thoughts welcome and thanks in advance

 

[Welder]

Interesting. From the chalk ref, I take it you're in SE England.

Firstly, learn one question. Why? Ask that of all the G3 qualified (ask to see evidence) plumbers who walk through your door and offer to do the job.

An experienced engineer, I would suggest, would see this as borderline and would want to call in a manufacturer to get their recommendations as to the correct way forward. Patently though, they would only do that if they too feel they can trust you.

Because of the way we use showers today, you will need to consider not what's happening now but the future too. EVERYTHING is overcomable even very low flow into a property.

Going back to your orig Q.

An appropriately configured & piped unvented HW system will deliver great HW flow for one shower but will, obviously, drop off when three are in use at once. That performance drop off is determined by issues such as pipework, showers used (cheap = more) and incoming supply pressure & flow.

An unvented system is now much more energy efficient than a conventional cylinder as insulation is so much better. By having a small circ pump then storage capacity can be increased too beyond the cylinder's headline amount.

In addition, you can now have multi-coil cylinders which could help offset running costs over the years. Most cylinders have a 25 yr warranty on them HOWEVER, they MUST be appropriately serviced EVERY year for safety, performance & warranty purposes.

With three bathrooms, unvented is def the way to go IMHO.

 

[sammathias]

Dynamic pressure?