Calling all plumbers advice and opinion required

Hi everybody, hopefully you can give some advice and experiences before i end up with something I don’t want

I want to utilise space my hot water storage tank is using ......so ..........
Unvented tank in loft or new combi boiler

Only ever had combi boiler so know a fair bit about them as well as issues running a shower or bath and somebody else trying to use hot water, so know the negatives.

I don’t know much about the unvented system but I do understand how they work and what the pluses are just don’t know the negatives

So I moved last year to a bigger house, which was built in 1983
The house has a storage tank which is badly insulated (a couple of red quilts covering it)
We want to utilise the space where the storage tank is so want rid of it

Options are

1 fit New combo boiler or
2 Horizontal unvented tank in loft in lieu of the water storage tanks

Ok I have looked at the existing loft tanks and reckon they are 2x 20 gallon tanks and a smaller one somewhere between 5 and 10 gallons giving me around 200+ litres of water in weight so I’m sure a 250 litre unvented tank should be ok weight wise? The platform looks sturdy enough and is not sagging anywhere, even though the upstairs walls are studding

Can you really run a bath without any bother? Run two showers with no problems plus kitchen tap?
Is it all hype and not as good as they are claimed to be
Would 250 litres be about right for a 4 bed house two bathrooms (1 bath 2 showers)
Are they any dearer to run than what I have now old copper storage tank
Any help advice before I make the plunge would be great

Thanks in advance

How much the tank can supply depends upon how well you can maintain the pressure. That’s partially a function of your mains pressure, feed pipe diameter and the outlet pressure you’re using.

I think the tank I had fitted is 250 litres - it’s bloody huge (upright). You need to check you can get it into the loft and then support the load evenly.

From what I read, 250 litres should be plenty for your needs.

You will need at least 2 pressure vessels for the unvented system. One for the hot water side and one for the central heating. These are service items which will need periodic checking, recharging with air if needed or replacement if the internal membrane fails. I would think about putting these somewhere accessible rather than in the loft.

I think you will also need some sort of drain arrangement for the system to vent if pressure get too high.

Ok thanks, so I have to get my pressure and flow checked before making a decision.

Are you happy with the flow rates mainly concerned about showers as that is what is predominantly used

Thanks for replying

Thanks for the info Hyperlink, I really need to have it all in the loft, can they be mounted in the loft I.e don’t need to be in a warm house, the tank would have to be a horizontal version due to space and ease of location I assume these perform no differently to a vertical version

Thanks again

Am I'm glad that I live in the sub-tropics when I read about all the issues that you lot have.

All we have is an externally mounted mains pressure 250 litre electric hot water system that is powered by "off peak" electricity i.e. it only heats up in the early hours of the morning, and we pay a lower tariff for this.

Yes - I’m very happy. My pressure is set at a shade over 2 bar for the system (the cold feed is restricted which balances the hot) and, with that system pressure, my piping and the mains pressure, the system works fine. I get a tiny (barely noticeable - slight change in tone rather than flow) drop in shower pressure when another tap is run. There’s no change in temp despite my shower not being thermostatic. I’m very happy with it.

Cheers MeanRedSpider

If only it was that simple here lol

Well...,while I’m not 100% sure if I understand your system arrangement, and not being strictly professional plumber, what you have now is heat exchanger tank I suppose...Why just don’t put one upstairs, with sufficient internal serpentine power dissipation capacity, they come well insulated and with 20+ years service life nowadays. On the other hand the non-vented tanks are essentially expansion vessels for the heating circuit, not the hot water tap circuit. Are there differences so big between the systems we use here or m’I getting lost... About the combi boiler option, the hot water output power directly depends on the the actual boiler heating power, they often came with the option to choose model with bigger internal heat exchanger tank, typically 100-150L, contrary to the 5-10L standard tank. And this is an option to avoid the additional loft tank. Programming it to maintain slightly lower than the heating circuit temperature gives you vast amount of bath-usable hot water yet taking advantage of the extra residual heat when the burner shuts-off.

You have/want something like this: ?
conventional

Yes thats what i have, its about getting rid of some elements of the system to free up space

The combi boiler creates hot water on demand and heats radiators to heat the house

The unvented system im thinking of installing removes the need for the tanks in the loft space ( the blue bits in the diagram you shared) so i can then put the hot water tank in the place of the blue parts something like this unvented

conventional vented system is the diagram you shared this is what i currently have and it all needs updating hence looking to change for unvented to free up space in loft to then place new tank in loft leaving me with an empty cupboard that i can use to make a room bigger

The combi is the other option and this gets rid of the loft tanks and the storage tank ... again freeing up a cupboard space for me to use

I hope that makes some sort of sense

My parents who are in Spain just have a combi boiler running off a gas bottle and a log burner i have never seen any other type of system in Spain or Sicily but i know they will exist perhaps with a different name

I guess they can be installed in the loft (mine arent) but as suggested they are something you want to check time to time. The CH side will have an expansion vessel with a pressure gauge and a valve to charge the system from the mains feed. you need at access this anytime you lose pressure from the system (leaks/bleeding rads/etc) so may be a pain if you have to go in the loft.

our neightbour also installed thier boiler in the loft to save space in the kitchen so that may also be an option whilst youre at it.

Yes i wanted to install the boiler in the loft but not sure if the hassle is worth it, its a detatched house with a hipped roof, so i would have to build up some sort of wall
Its do-able but hassle.

I really need to get somebody around to quote for installation and see what they think i would do it myself, but i am aware it needs to be done by a gas safe G3?engineer for insurance to be valid.

I did a course and had a ticket to work on steam boilers around 2006, i have no idea if it is still valid,i very much doubt it.

Unvented is still my preferred option at the moment!

Unvented is the way to go for modern system in my personal opinion too. Price, efficiency, reliability, service and hygiene are just few reasons to mention.
Speaking of the expansion tank, being the unvented rubber diaphragm type, it can be placed everywhere you choose in the house, just needs one pipe connection to the heating circuit, isn’t big or heavy piece either. They last with ease more than 10 years under normal conditions, are cheap and servicing/changing is simple job - once a year before the start of the heating season check the pre-charge air pressure, typically 1.5bar, car tyre valve there. If air inside at the specified pressure - it’s OK, if water blowing off the valve - change needed. If you choose to change the boiler almost all of the newer ones come with integrated expansion tank and you need to change/add bigger one only if the house has very large (water volume) heating circuit.
Speaking of the hot water tank - the situation is a little bit more complicated, but similar. Being unvented you can put it everywhere you choose, needs two pipes connection to heating circuit and two to the tap water circuit. There is option to add solar panels, but that’s another story yet. There are few BUTs. You want it at higher temperature possible to be able to keep it small but have enough hot water available, so next to the boiler is the best place usually. Further in circuit, read further away from the boiler, lower is the accumulated heat, bigger it has to be, but, that’s only true depending on various factors - primarily the method of connecting it to the heating circuit, if the heating is operative 24h and the type of heating circuit itself. Later on, if you change the boiler then choose one with bigger integrated hot water tank, as I mentioned in my previous post, of course the boiler itself is bigger, but not substantially, and the tank is at the best place to be - next to the burner, so it’s always at the specified temperature, the most efficient solution.
These are few examples of what I’m speaking about:
1
2
3
4
These are an oil and gas heaters, in the oil one is easier to see the concept
A
B

Then, I’m not sure about the UK legislation, but for only modding the water/heating system Gas-license shouldn’t be required, for changing the boiler - yes, but on the other hand that’s not job for one to do, not only because the license, but also because the first start-up, adjustments and to have valid guarantee.
As for the log burners, yes, there are the so called fireplace (-inserts) which have “water shirt” in the fire log walls and can be connected to the heating circuit as primary or auxiliary heat source. So like a fireplace but also heating the radiators, not so effective though, few major drawbacks there:
C

The reason the U.K. requires some form of sign-off on mains pressure systems is that they can be incredibly dangerous due to the volume (of air possible) and pressure. Water is incompressible and therefore fairly safe but air is a lot more dangerous.

I paid a qualified guy to do mine - then spent several months trying to get him to correct the bits that didn’t actually meet the regs. Threat of getting the building inspector to look and dissing him on the rating site finally persuaded him to come back and make it legal.

Well, let me be clear, I’m not encouraging anyone to perform diy jobs without the proper knowledge and training, it is matter of advices about given problem. Also won’t enter in polemics of why there are certain restrictive, protectionist, etc. requirements in our respective countries.
Speaking of the incredible dangerousness of the water supply and heating systems, think of it as far less dangerous than a car cooling system. These are not alike Mega Watts industrial steam boilers. Could reach certain level of risk if all hydraulic, thermal & electric protections fail all at once. And that’s equally true for vented and unvented systems. Take in account that all standard elements used are tested to withstand something alike 10bar@100°C, or more, before they find place in the market, and that’s way below the working pressure and temps of house system. About the air, don’t know, the only air we are dealing with in that case is the one which the expansion tank contains, it is separated from the water by the means of a rubber membrane, generally something like 5-10L @ 1.5bar. The air is unwanted guest in the water heating systems as we all know.
So, my words to be taken only as advice. A proper query with local professional (two,independent, at least) should lead to the final decisions.

Wont do it myself due to insurance

I was qualified to work on industrial boilers at work which are used on sewage work digester's, along with COMPEX DSEAR so appreciate all the safety factors etc.

I have not touched one for a fair few years now, I would of installed it myself, if it wasn't for the insurance side of things, they are very safe if installed correctly

I just didn't know how they compared to other types of heating systems in the home hence the questions!

Appreciate the note of concern from you both though so Thanks again for your input