New hot water options

[Mark M]

Currently I have a hot water tank and a pump that powers 2 showers. Water pressure on the showers is great (3 bar I think the pump is) however the pressure on the hot water at the upstairs tap isnt great due to gravity (downstairs is fine). The main downside with the water tank is obviously that it can run out of hot water. There are 2 adults and 2 kids (6 and 2). Im extending the kitchen and will be moving the boiler into the garage so thinking of whether its worth replacing the water tank with a new one as its >25 years old or looking at another option. I dont think I'll get much longer out of the boiler either as its been patched up a few times already.

I think my options are:

1) replace with a new hot water tank, perhaps a larger size for when the kids grow up as the current one runs out at the end of a 4th shower if we have guests staying.

2) replace with a pressurised system. Benefit would be good pressure everywhere but probably the most costly option I think?

3) change whole set up to combi system. Benefits from on demand water but assume pressure would be lower at the showers and wont run 2 showers at the same time which may be a deal breaker for business mornings now I come to think of it.

Any feedback on the above? Is there anything Ive missed or not thought about?

 

[Mark M]

AFAIK you can't run a pump for powering showers with a combi boiler. You obviously won't be relying on gravity as it will be mains pressure, so make sure your mains pressure is pretty good.

Hi, yes I wouldnt be reconnecting the pump if I went the combi route

 

[Mark M]

Before you rely on direct mains supply for either a combi or un-vented hot water cylinder you should check mains pressure and very importantly also the flow rate, and several times during the day as it can vary (pressure testers are cheap and flow can be checked with a bucket). If the flow is not adequate then you need to check pipe sizes, both into the house and inside as I've often seen a good size supply restricted by small internal pipework or fittings.

We wanted to go un-vented hot water cylinder as we don't like noisy pumps and have three showers. Our old mains water supply pipe showed very good pressure but inadequate flow due to its small size. In our case we had to upgrade that supply (32mm MDPE) and water meter and we made sure all internal pipework sizes and controls didn't impact flow. The result is enough water to easily drive three showers each potentially using 25 litres a minute simultaneously with no pump noise.

We were a bit over zealous, but its worth checking these details and considering cylinder size and boiler about as it can make a huge difference. We found most plumbing companies didn't test or consider any of this and in fact some of their comments were absolute rubbish and defied the laws of physics!

Ive read a few things regarding flow rate and pipe size internal and external. I'll check out the pressure and flow rate before proceeding with any option thanks.

Having had all three types, i wouldn't hesitate to say pressurised is by far the best, unless you want to save a few quid, then get a combi

Megaflow is night and day better than a combi

Do you have a rough idea of cost for a typical install? I appreciate there are a number of variables but just some ball park figures would be good to start a budget.

Another couple of quick questions for anyone with a hot water tank or unvented system:

A quick Google suggests the average shower uses 50l of water, does that seem correct? If so then I guess Im looking at a 250L cylinder to future proof it for when the kids (2 boys) get older?

The current water tank is in a cupboard on the landing. Im unsure of the current size of water tank but can the unvented cylinder go there or does it need to go in the garage? There currently isnt a 32mm cold water feed to the upstairs cupboard so would need to route it through a few rooms to get there. Any damage wouldnt be much of an issue as the rooms are next on the list to redecorate. Garage space is fairly limited but if its better to put it there then so be it.

 

[Mark M]

That's a bit low in our experience but we like nice powerful showers and don't rush. We don't run our showers at full power (which is around 25L per min as per my earlier post) so its more around 15-20L per min and our showers range from 5 to 8 mins.

Taking the 15L that's 75 to 120L I expect around half or a bit more is hot water which we have set to 60 degrees so 40 to 60L of hot per shower. We find our 250L cylinder due to a shallow airing cupboard but with a decent coil KW recovers fast enough to never have any issues even with 2 x 2 showers with only a few mins between.



Bear in mind the external versus internal pipe size. I believe the largest common MDPE water pipe size to most houses is the 32mm we have and the internal size on that it is 26mm not including any inserts for fittings.

We then have the initial cold feed pipework as 28mm copper which has around 26mm internal size. Once it splits to hot/cold for feeds it goes down to 22mm copper each and then mostly 15mm copper for the individual showers/sinks. We did all this to make three concurrent showers work well so a bit less should work fine for two.

Thanks for your assistance so far, Im sure there will be more questions to come! Glad I found an expert on the subject

What spec is your cylinder? Just been having a very quick look on Screwfix and it seems you can get Megaflow that are indirect or direct with 2x3kw, 3x3kw and 4x3kw options with only about £100 difference.

 

[Mark M]

Those ratings appear to be the electric elements, the primary coil for an indirect cylinder is usually 15kw going up to over 40 for some (assuming the boiler can manage).

I looked at Megaflow but their cylinders were a fraction too wide or else a bit too tall and some had internal expansion vessels which I didn't want. In the end we went with another brand that was a perfect fit but only had a 20kw coil. In theory this calculates to heating 250L from 5 to 60 degrees in 48 mins. In any event the cylinder can cover 4 good showers and recovery every 10 to 15 mins would yield another shower and for us that was enough.

If we had a better coil output KW then we would need another step on the boiler and its pipework/pump to make full use of it. It's easy to over spec one area and be limited elsewhere hence my comments about pressure and flow for cold supply. I have neighbours with 40kw non combi boilers with pipework and pump that cannot deliver enough water from it to yield more than 20kw!

Probably a daft question but what do you mean when you say 15kw to 40 assuming the boiler can cope? I assumed that indirect the boiler heated the water and for direct it was the heating coil?

 

[Mark M]

modern combi boilers are reasonable and should address your problems.

Will look at the cost of the 2 but not sure I want "reasonable", especially going from a great showering experience with the shower pumps. When we have guests stay over they always comment that the shower is like a hotel shower whereas I guess they are used to a combi shower at home. Will all come down to brass tax at the end of the day though.

 

[Mark M]

I've done combi twice and found it struggled to cope with what amounts to 4 adults and a teenager. Anything else happens in the house (flush the loo, washing machine fills up) and the pressure drops enough, even worse if two of you are showering at the same time. Best case you get a low pressure shower each.

So this when we moved to a new house with a 20 year old system I went pressurised and have a megaflow pressurised system with a Worstester boiler heating that and the radiator. Also changed the showers to thermostatic controls. Its night and day for us, everyone gets a hot high pressure shower with very little pressure drop and it doesn't matter if somebody flushes the loo downstairs now. When one of the girls really goes silly with a long shower we can run out of hot water but it recovers quickly ready for the next person.
The downside is you don't have endless hot water but it recovers quickly, the up side is mains pressure hot water all through the house, we have good pressure at our place. It was about 1.5k more expensive than a straight combi version but so much the right decision for me.

Thanks for the info, if there is £1.5-2k difference then Id be happy going with the pressurised system over a combi. Just had visions of it being much more expensive!

 

[Mark M]

I think Ive decided that the pressurised system is going to be the best option to go with. The plumber is going to sort a quote out but a couple of further questions if I may:

1. He has suggested going with Main Heating boiler and cylinder. Apparently they are part of the Baxi group? Any thoughts, opinions or experiences with them?
2. He said the best location for the boiler will be in the loft (currently in the utility room) and the cylinder in the airing cupboard where the existing hot water tank is. I had originally planned for the boiler and cylinder to be in the garage but have no real preferece however assumed it would be more straight forward running the mains cold water from the stop **** (kitchen) to the garage. Any downsides/issues to the boiler being in the loft?
3. Just curious but do I need a direct or indirect cylinder?

 

[Mark M]

The loft is partially boarded out but can board out more of it if need be no problem.

The showers are used most but its not the end of the world waiting 10-20 seconds for the hot water I guess so not a deal breaker either way. The plumber said it would be cheaper to install in the loft so assuming there is no major issues I'll probably just go with that.

 

[Mark M]

Lofts are okay if access and lighting is good and its easy to connect up to existing waste for the boiler condensate drain (not into guttering down pipes!). Working in lofts in the summer can be a nightmare so consider any servicing outside of the sunniest months and hopefully most boiler issues occur under load in the colder months.

An indirect cylinder is what you need - boiler doesn't heat the actual hot water you use, just its primary circuit water which in turn heats the hot water via a loop of pipe in the HW cylinder so indirect.

Thanks. Can I just clarify your last sentance as this is where Im getting lost off with the whole direct vs indirect method. So the boiler has 2 jobs, first to heat the radiators and second to heat water that goes through a primary circuit inside the cylinder that heats the water in the tank?

So does a direct cylinder have an element and doesnt rely on the boiler for anything?

 

[Mark M]

Ok so Ive decided to go with the pressurised cylinder route and the plumber is coming roud to Friday to price it up. What should he be checking when he comes? Ive seen it mentioned in other threads but I think its is pressure and flow rate? Flow rate can be checked by timing how long it takes to fill a bucket I think but not sure about the pressure?

Thanks