Economy 7 immersion heater tank!

[AdvanceHelpline]

Bear in mind you need metal discharge for unvented - search "electric thermal store" you will get mains pressure hot water without the need for a metal discharge to an outside wall at ground level

 

[pebbles36]

Ah ok not sure what that is, will do a search on that, will the system be all ok on a first floor flat though?

 

[Madrab]

OK, if you're now considering an un-vented again then look to price one midrange and look for the longest warranty period, a lot do 25years. Only thing I would say is try and avoid a megaflo if poss. Again though you need to have your pressure and flow tested first.

A thermal store is a cylinder of water that is kept at a hot temperature all the time, the cold water then runs through a coil sitting in the water, it's advantage is that it sits at atmospheric pressure like your old cylinder. Its main drawback is that the water needs to be kept at a constant temp all the time to ensure that the hot water it produces is consistent, not sure how expensive that would be using electric. A direct unvented you would only need to heat the hot water you use.

Oh and the un-vented discharge pipework does not need to be at ground level, suitable systems can be discharged into a waste system using a specific type of waterless trap and polypropylene (plastic) pipework can be used as it is stable at high temperatures. That can then ported into a soil vent pipe but again your installer would advise about all that.

Do a bit of digging and get the advice of your installer and take it from there.

 

[pebbles36]

Hi Madrab, yes i am now certainly going to go ahead with a un-vented, been interested in what you say about them and certainly a good investment to make! Also been looking at them on the web and seen the 25 year warranty ones! What size tank would suit a 2 person household with mainly the shower being used in the evening? Not really sure to the litres i really need?? Thanks

 

[Madrab]

It depends P, if a standard shower is used then around 70 Ltr's per person would be the norm. So say a 150 Ltr cylinder. If you are taking a shower one after another then you do need to allow it to recover, though modern cylinders recovery much faster than old ones. What size is your current cylinder and does it supply a suitable volume of HW, all things considered?

Is the property all electric?

One other thing I will add at this point, an un-vented cylinder does need checked by a qualified engineer once a year, just like a boiler but the cost of that service shouldn't be at all restrictive.

Rob

 

[pebbles36]

Not sure the litre capacity of my tank as it has no info on it! Yes my place is all electric but recently had a new thermostatic shower fitted but the hot water pressure is very poor and it would be useless i think if it had a pump fitted as i guess it would rapidly empty the tank so that is why i am looking for a better alternative to a combination cylinder plus the tank i have is about 30 years old so it is time for a upgrade i think! Better to be safe than sorry so a annual safety inspection is good for me! Thank you for your help!

 

[Madrab]

What size is the lower larger section of the tank, height - width?

Glad to help pebbles. I think your starting point would be to get an experienced plumber who's seems receptive to working with you and have them do a survey on your system and just see what you have, what your supply is like and therefore what is achievable and available.

To be honest, whoever installed the thermostatic shower should have indicated that it wouldn't work well with your current setup, so you'd kinda want to avoid using them

 

[pebbles36]

My tank size is approx 800mm height and 500mm width.

Yes certainly wont be using the plumber again who installed my shower but did need a new tank so a blessing in disguise really!
Believe it or not i have phoned a couple of very good heating engineers i know but they are not qualified to fit un-vented tanks so been googling them and alot come up under the website "Checkatrade" so not sure wheather it is a good idea to pick one from there or not but need to get someone in to have a good look and go from there! Again thanks for the help Rob much appreciated!!

 

[Madrab]

OK that should be good for about 120 Ltrs of hot water so that gives you your starting point. Targetting around the 150Ltr mark would be good for 2 people IMO @ mains flow.

 

[OwainDIYer]

Always aim for more stored hot water with E7 - any you don't use will keep warm for several days. New cylinders are very well insulated. Also a higher pressure sshower will usually use more water anyway.

 

[stem]

Whilst the advantages mentioned above are true, I lived with one for 9 years and sadly it's not been a happy experience for me. I moved into the property in 2007 which had been a new build in 2005. As well as the annual service I had to call someone out to it because....

At 5 years the membrane in the expansion vessel failed and it filled with water where the air should be. Because it was mounted horizontally the extra weight snapped the vessel clean off the pipework and caused a flood.

At 8 years old, the cylinder split causing another leak and the whole thing had to be replaced. They can't be made from nice soft flexible copper apparently because of their increased operating pressure, and so are made from wafer thin stainless steel instead.

There have also been at least two instances of the pressure relief dripping.

So, because of my previous experience of a vented cylinder and header tank which in 20 years simply needed a new washer in the ballcock which I could do myself immediately and for about 25p compared with my unvented experience means that given the chance it would be vented for me every time.

This may not have anything to do with the type of cylinder, but the immersion elements failed frequently. As well as the initial 2 elements there have been 4 replacements, and even this has to be done by someone suitably qualified because of re-pressurising the system afterwards. But to be fair I can't compare this with a vented cylinder, because the one I had was connected to a gas boiler and I didn't use the immersion.

 

[AdvanceHelpline]

Well thermal stores are vented - no expansion vessel to maintain. They are heated overnight on cheap tariff for use in the day so not too expensive to run. Your call - but I would question wisdom of discharge into soil stack as they have been known to collapse with unvented relief valves on full bore at high temperatures. Most guidance suggests metal discharge to ground floor

 

[Madrab]

Most guidance suggests metal discharge to ground floor

I'd have to disagree. All guidance suggests metal pipework discharging to ground level though most then require shielded pipework but they also suggest high level discharge to a flat roof/hopper or discharge through suitable plastic to a SVP. Most Plastic SVP's are tested to withstand hot water for a given period of time and no issues with Cast SVP. All discharge methods are just as acceptable as the others. It's very rare that a SVP collapses under an un-vented full flow discharge due to their manufacturing testing and proving processes and the cylinder's safety features but again this comes down to the installer confirming and checking that the location is suitable to accept an un-vented system.

Thermal stores have their own issues. They may have a separate cold feed and expansion tank above the cylinder so tend to be quite a bit larger or need a separate F&E cistern, they can be susceptible to issues with their blending valves so HW can become erratic, the heat really needs to be maintained within the thermal store during the day as well as overnight to allow it to be efficient and provide enough hot water later in the day when you need it, they are susceptible to sludging/scaling up, etc.

TBH, if you want to you can easily find issues with any system and could go back and forward all day.

Please don't mis-understand, I am not dissuading the use of a thermal store and they can be excellent in certain situations, I just wouldn't recommend them within a flat where space and height can be at a premium & electricity is the only power source. Out with Economy 7 it can also be very expensive when hot water runs out at peak times and the water in a thermal store needs to be maintained.

Pebbles - as mentioned a few times I would recommend you get someone in that has experience with these systems and allow them to suggest what the location can support in the first instance.

 

[pebbles36]

Yes Madrab that is what i am doing now, trying to hunt down someone who can take a look and advise on the best option for me!

 

[Madrab]

Apologies pebbles, that was not mean to sound as if I am telling you what to do and do it now!! Far from it, at the end of the day it's just advice. Most of that was in counter to another comment and not directed to you. I was only trying to point out to others that there is usually a good and bad side to every solution if looking hard enough and that shouldn't drive a solution alone.

.... and that most solutions can only be best judged onsite.