Which unvented indirect cylinder to buy?

[loizos]

I am looking to replace a traditional hot water cylinder with an unvented indrect system.

I've been researching some options in terms of what manufacturer and size to go for. The cylinder will go in the garage and there's ample space to put a bigger unit / external expansion vessel if necessary. I have a Vaillant Ecotec Plus 637 boiler and I'm leaning towards the Vaillant Unistor but unsure what size to get.

The property is detached, 3 floor, 6 bed + 1 bathroom today. I plan to add another bathroom and 1 (max 2) en-suites in future. This is a family of 2 adults + 3 young children, so looking for something that will be efficient to run now and can cope with more demanding requirements in 10 years+.

Some questions:-

- Is the Vaillant UniSTOR 210/260/310 Litre a recommended unit for my boiler? What size should I go for 'as a minimum' based on future requirements

- If we don't need the additional capacity today, is there a significant additional running cost of having a larger cylinder that is 'overkill' for now? i.e. is it going to sting me in fuel costs to go for the 310 over the 210/260 just so I don't need to upgrade in 10 years?

- Generally, would experts recommend Vailant over OSO (and others which offer separate expansion vessels) based on my requirements?

Thanks!

 

[virgilns]

I had the same question ages ago. Much are much of a muchness...(i know that doesn't help...)

Megaflow were over twice the price of the cheaper 'external bubble' cylinders and need the internal buble 'recharging' every 6 months to a year by the user, whereas I thought I'd rather just replace my 'external bubble' every few years when it inevitably dies...i went for a 250 litre telford tempest tank on the basis that all the bits were easily swapped out if a bit broke. it was a good size and fitted the location i'd chosen

I did a long analysis of most of the popular tanks available...as I was fitting myself (you have to be competant/qualified to do this)

My father in law who wanted an unvented got a plumber in...so he got fitted what the plumber suggested.

So my conclusion is:

Better quality tanks seem to have thicker insulation that cheaper tanks, but most quote very similar heat loss rates (better ones ARE slightly lower)

Check the re-heat time for the coil but again - all fairly standard and only make a difference if you have hot water priority and aboiler powerful enough to heat it...or you are just putting x kw into x number of litres of cold water...

You can pay for bigegr coils on some tanks but they are very expensive and may not provide any benefit if your boiler is to whimpy...

Guarantees:

Some provide lifetime on the cylinder, 2 or 3 years on the 'safety valves' and some 'just 25 yrs'

All the ones I looked at need servicing every year (which they should be anyway) to maintain the guarantee, or it's invalid after 1 year anyway! My mate's megaflow must already be invalid as he's had it 18 months with no service !!

I went to town working out flow rates, etc etc...now it's in it works very very well and it's probably as mucgh down to a decent install than the tank.

I've got 8 bar static preasure and 32mm mdpe /28 mm copper all the way to the tank so my flow rate is above what teh tank could ever use. My mate's and faterh in laws are 15mm mains so they may see a drop in flow rate if they used multiple showers at once...

One thing I didn't know was that I may not have a small compatability issue with my vaillant 637 and hot water priority with weather control (still reading up on this, askign questions) so this may decide your make for you.

Go as big as you can fit in (250 or 300) as there's not much money in it and once it's up to temp there's not much in it heat loss wise...upgrade your mains if you need to (plumber will tell you your flow rate)

OSO were my 1st choice excluding price, but they use dedicated parts (bubles etc) so were much pricier to repair than a 'cheap old' Telford, santon etc....

 

[loizos]

Thanks for the advice. I've still got 15mm mains but would look to upgrade that in future when it's needed too. So I think I'll go for a 250/300.

When you say there's not much money in it heat loss wise between the two, do you mean there not much difference in reheating costs between the 250 and 300? I'm already getting extortionate fuel bills and want to get this as efficient as possible.

Thanks for your help again!

 

[mfarrow]

http://www.vaillant.co.uk/stepone2/data/downloads/0a/44/00/uniSTOR operating.pdf

See section 8. There's a ~10% between them all. Not quite sure what a kW/24h is though, as written it's a rate increase.

 

[CBF]

why don't you ask the installer with the G3 cert that you HAVE to use what his recommendations are

 

[indus]

why don't you ask the installer with the G3 cert that you HAVE to use what his recommendations are

Why can't the op do some homework first? Do you personally just blindly follow any advice you are given just because somebody has a certificate?

If you want to buy a new car do you just buy the one the salesman recommends or do you engage your own brain as well?

 

[CBF]

because they are asking questions on here that would be easily answerable by getting the installer around for a quote, then they are better informed & won't need to ask questions about things that at the mo they have no idea about, plus the questions being asked leads me to believe that the OP intends to fit it themselves which isn't allowed (or you will have to spend a small fortune getting BC to sign it off & most BC inspectors i've come across haven't the first clue when it comes to unvented), taking your car idea, do you go along to BMW & ask for a complete blueprint of their cars so you can build your own.

edited: added info

 

[indus]

because they are asking questions on here that would be easily answerable by getting the installer around for a quote, then they are better informed & won't need to ask questions about things that at the mo they have no idea about, plus the questions being asked leads me to believe that the OP intends to fit it themselves which isn't allowed, taking your car idea, do you go along to BMW & ask for a complete blueprint of their cars so you can build your own

The thing is when you ask an installer these questions you get one persons opinion, and the validity of an opinion varies according to many factors.

The benefit of asking the question on a forum like this is that you get the opinion of many experts.

Going back to the car analagy, no I don't ask for a blueprint of the car. However I do my own homework to see what the reliability, resale value, real world mpg etc is like. And I don't walk into a showroom and just buy the car the salesman recommends.

I also never buy any of the other scam products they sell like paint protection, gap insurance etc etc even though they always recommend it.

If the op is thinking of fitting it himself then that is not something I condone.

 

[loizos]

Thanks for the feedback everyone.

Regarding fitting it myself, that's not the case - I'm just trying to be well-informed because I'm the one that has to live with the decision I make.

Ultimately in any walk of life, an expert's opinion is biased to their own experience. I doubt a single plumber will have experience of all the different options on the market which is why I'm asking the question to a larger audience. After all, I see experts asking other experts questions on this and other forums all the time and ongoing debate, so why should I accept what just one person is telling me?

On the car analogy, my mechanic recently told me all Audis are rubbish - they're plastic inside. Everyone I know who own Audis say they are great, cheap servicing costs and that they will never buy anything else. See my point?

Anyway, appreciate all the advice. There doesn't seem to be much in it as the first poster said, so I'll go for the bigger one - the 300litre.

Thanks again.

 

[indus]

That post is spot on my friend. As you say you can clearly see from this forum that the professionals often don't agree with each other on the best way to do things.

They differ in their approach to problems and have different preferred hardware. Nothing wrong with this as there is more than one way to skin a cat.

However it does show that it may not be the most sensible approach to just accept what the first bloke with a 'certificate' that walks through your door tells you.

 

[CBF]

I think you misunderstood me, I wasn't saying anyone shouldn't find out info, but it is always wise to get the opinion of a professional who will be able to answer alot of questions, for example have you had the flow & pressure tested on the incoming cold main ? because the OP may find that either one or both may not be suitable to change to unvented & therefore making this whole thread moot

 

[algas]

Why don't you fit a smaller one for now, when you fit your new en suites add another of similar size linked in tandem, you could fit iso valves on the primaries so that you could just use the one if the extra capacity was not required, also bear in mind that a cylinder with an internal "bubble" has less water capacity than one with an external exp vessel

 

[virgilns]

The thing i like about this forum is that you get advice based on what people think is best...not what they are about to fit...kind of best case scenario

My Father in law wanted his cylinder in the loft next to the boiler and was advised to have a either a 180 or 210 litre model.

Now they are caterers so use a LOT of hot water...I suggested they ask why a 250 litre was not being suggested, but the guy just said 3 bed house one bath one shower 210 is plenty.

Father in law goes along with that.

Come time to fit the cylinder and the loft hatch is JUST slightly too small...but they really wanted the DHW cylinder out the bedroom cupboard to make more space. Fitter said no option, but to put in in cupboard.

If they'd have looked an known about limline cylinders they could have argued and said 'sorry, but if you look at a different make, you can get a slimline on in there and put it where we want it'...they didn't do any research and got lumbered with something they didn't want.

The problem is that the professionals on here have a vast knowledge between them all and they kindly share with us mere mortals...some of the professionals in the outside world just want to get the job done as easily as possible and push the customer into 'known territory' for ease...

nowt wrong in hiring a professional to do the job, but I ALWAYS like to know what ALL my options are before letting anyone do work for me....

 

[loizos]

The professional is giving me the choice of which brand to install - he thinks they are much of a muchness. He has checked the flow rate. There's a 15mm pipe coming in but the flow rate is good enough. He said I may need to upgrade in future when I have more demanding requirements.

It's really my decision on whether I want a larger one for future requirements and pay more energy costs in the meantime, or go for a smaller one now and add to it later as was suggested here.

I am now learning towards the latter option since the second could even use an alternative heating source in future without me having to buy a unit that is "solar ready" now. Is my logic flawed?

Thanks for that advice. I think I'm ready to have a more informed conversation with my installer now.

 

[indus]

What is your flow rate?