Can/should I switch hot water systems?

nicw_3

Hi, looking for some advice as we are getting mixed messages from the people we've had round and I'm trying to make sense of it all!

We live in an old house (1880) which currently has a conventional gravity fed hot water system - 3 bedrooms, 2 bathrooms, though the shower in the second is only ever used if we have guests staying. The boiler is on its way out, and rather than paying to repair it we are considering changing our system.

Currently we have a 3 bar whole house pump - this is probably too much but the plumber we used when we replaced the old broken one didn't warn us of the likelihood we would be using up most of our hot water with one shower, which we are now doing! At any rate, our shower is obviously great with this pump and we know any change is likely to be a step down (and possibly require changing the shower head), but we're okay on that. Currently paying quite a lot in electricity bills running the pump all the time and constantly reheating the inefficient hot water tank.

Ideally we'd like to switch to a combi for better efficiency, control over the hot water and gaining the space in the airing cupboard, which could be changed into a wardrobe in the small bedroom next door. Open to using a mains booster pump with one as well, if there's any use in that. We've also been advised that an unvented cylinder system might work better, and are open to this too (particularly new smart ones that allow you to control how much water is heated).

The issue: our water flow measured at the outside tap is 10L/m, with 2.5 bar pressure. We have asked for it to be measured at the street and waiting for that to be done and could look into upgrading that pipework if the numbers are much better at the road.

We've been advised we *could* install a combi, but it wouldn't work to full potential and using any other tap etc out of the question. All three people we have had round (a plumber, a boiler repair engineer, and a British Gas engineer) have recommended unvented systems, but from my understanding this will still only give us the pressure and flow that is available at the mains? The Megaflo website says unvented manufacturers basically agree you need 20L/m, regardless of what their minimum specs say - is that true?

So if anyone has any advice on whether we'll still get a decent setup out of either a combi or unvented, or any other route we could go (I keep reading about accumulator tanks but unsure how much one would help in this situation?), I'd really appreciate it!

Jeepers_Creepers

Hi Nic.

As you clearly understand, both unvented cylinders and combis rely on a good mains flow and pressure to deliver the goods. And 10lpm is certainly not 'good'. It's pants. Rubbish. Unusable. Pitiful.

The interesting thing with your mains readings is, the pressure is pretty good at 2.5bar (not amazing, but 'good'), so that suggests to me that the cause of your poor flow is very possibly a squished incoming mains pipe. I wonder if it's possibly still lead?

So, you are doing absolutely the right thing in having the flow and pressure assessed at the street. If this turns out to be a lot better - say >20lpm and 3barish - then you have the choice of combi or unvented to choose from. Fill yer boots.

There are pros and cons to combi vs unvented. Briefly, these are:

Combi: unlimited hot water. Cracking shower (but really only one at a time unless a very biggie combi). Space-saving - no cylinder cupboard used up. Lower cost to fit. More moving parts - generally less reliable over time.

Unvented: Usually better overall flow - you will likely be able to run 2 showers simultaneously, tho' possibly with some compromise (it all depends on mains supply). More costly to install, and cylinder should have G3 service each year. Potential to add additional heat sources - Solar panel, stove etc.

If you find that upgrading your mains supply pipe still won't give you adequate P&F, then a solution is as you say - a pumped mains accumulator. Challis, Grundfos, Salamander etc make them, and they can work in different ways. I'm quite taken by the Challis - this pumps mains water into a pressurised tank, and this then supplies the house under its stored pressure.

The Grundfos, I understand, allows a tank to fill, and then a pump delivers this unpressurised stored water on demand to the house - so a pump runs whenever water is being used. The Challis sounds better to me - I know someone who has the Grund, and the noise is quite noticeable every time a tap is run. The Challis should only fire up occasionally, to repressurise the tank when needed. But you'd need to carry out your own research on these should you be considering them. These accumulators can go in the garage or outbuilding.

BUFF

If you wanted to, in the meantime you could limit how much water your shower uses by installing a flow limiter or changing shower head or of course changing shower behaviour (shorter or not continuously running whilst lathering up etc.). You may be able to get water saving stuff free/discounted depending upon where you live. https://www.moneysavingexpert.com/utilities/cut-water-bills/#gadgets

nicw_3

@Jeepers_Creepers I thought I had posted a reply last night but apparently not! Huge thanks, that's incredibly helpful. We heard back from an engineer yesterday who said exactly the same, neither system will be any good with what we're working with, so he's coming round today to talk accumulator tanks while we wait to get those street readings. Very possible the pipes are quite old since we actually tried to get the measurements there in September, but the stopcock was so old they couldn't take them and had to have it replaced. By the time it was done we'd already replaced our pump and moved on.

nicw_3

BUFF, it won't let me @ you or quote you for some reason, but thanks! We probably will change the shower head whatever we do as it's using a ridiculous amount of water - unfortunate that we didn't realise beforehand as we've just had the bathroom done so will now want to find something that doesn't ruin the look too much.

Jeepers_Creepers

nicw_3 said:

@Jeepers_Creepers I thought I had posted a reply last night but apparently not! Huge thanks, that's incredibly helpful. We heard back from an engineer yesterday who said exactly the same, neither system will be any good with what we're working with, so he's coming round today to talk accumulator tanks while we wait to get those street readings. Very possible the pipes are quite old since we actually tried to get the measurements there in September, but the stopcock was so old they couldn't take them and had to have it replaced. By the time it was done we'd already replaced our pump and moved on.

Cool.

Obviously the best solution - by far - is to upgrade the incoming mains, as this is 'passive' and has no moving parts! And takes up no additional space.

Do you have a meter fitted? If so, I think that's where they could measure the 'street' p&f. If you don't, would you be happy to have one fitted?

nicw_3

@Jeepers_Creepers Yes, we had them install a meter when they put the new stopcock in. Any idea what upgrading the mains could roughly cost? Assuming there's a fair number of factors, but it's a fairly standard distance from the street, ie enough to park a car. Water company have said they'd contribute £250.

Jeepers_Creepers

No idea, Nic, but it usually comes down to how hard it is to run the pipe - the actual materials cost is little.

Are you up for some DIYing? Could you dig a narrow slot trench around 750mm deep (that's deeper than you think!)? It's also possible to 'mole' a pipe hole, and this is often done when you want to minimise damage to the upper surface.

And you need to know where the pipe currently comes in to the house - or have an alternative route ready.

Essentially, therefore, you'd dig down at the house wall at the location you want the new pipe to come in (very likely the existing location) and ditto at the meter. Then you decide how you are going to get from one to t'other.

(There are guidelines on how to protect the pipe - pea shingle, that sort of thing - but it's easy to follow.)

nicw_3

@Jeepers_Creepers Unfortunately I don't think that work is in my limited DIY wheelhouse! We've just had the heating engineer round, who said it's probably at least £2k worth of work and quite a big job. He also thinks that while the flow might improve significantly, it's unlikely the pressure will make enough of a difference.

He said we need at least 3.5 bar for either a combi or unvented system to work decently in our house. Since we've got 2.5, he's recommended, as you did, a pumped mains accumulator to get the pressure up. He's recommending unvented over a combi, or perhaps a combi with storage if we're set on that. So off to research the ones you suggested before!

Jeepers_Creepers

I can confirm that these pumped accums do work - they will sort any low flow/pressure issue. (It'll also be cheaper than £2k!)

Do you have a garage or outhouse to fit it in?

nicw_3

@Jeepers_Creepers We have a garage, though it was a later extension and the plumbing work around it is a mess - might be more trouble than it's worth to put it in there and then worry about getting plumbing to and from it. We have the space in the loft, including enough height to have it on a platform for hopefully better soundproofing than the pump we have now.