New Combi Boiler - Want More Hot Water but how?

[Krobar]

Hi Everyone,

First post here and I'll prefix this by saying I will not be doing any of the install, I just need to know what will provide a really good shower output from a large shower head. One bathroom only, 3 bedroom detatched.

Currently have a 16 year old worcester 240 which seems to have some hot water problems anyway, heats the house quite quickly though.

I'm after a decent 20+ ltr/min shower output. Mains pressure is high, went off the scale on the plumbers measuring thing and he said pressure wont be an issue for whatever solution I choose.

Can anyone give me thoughts on any of the following options:
Worcester 440/550CDI Combi
Valiant 937 Storage Combi
Valiant 838 Combi
Glow Worm Ultrapower 170SXI Combi with Cylinder thing
Glow Worm Xtramax HE Storage Combi
A standard Boiler with a pressurized cylinder

Any thoughts or suggestions would be appreciated. In particular I am unsure of how a storage combi is better? Also, what sort of rate can you drain the cylinder in a Ultrapower 170SXI?

 

[Agile]

Either you or your plumber seems to be confusing pressure and flow! I hope its not the plumber.

You need to read the specs of those boilers. Only the storage combis will provide a flow rate of about 20 li/min and even then only for a few minutes.

The obvious solution is an unvented cylinder. But a 200 li will only give 20 li/min for 10 minutes before it goes cold.

Tony

 

[Krobar]

Hi Tony,


Thanks for the reply. The plumber measured pressure I think since it looked like a pressure guage, I assume I can measure flow rate from the cold water tap in the bath with a big bucket and stopwatch?

200 litres at 30ltr/min for 7 min would be fine

Are Ultrapower SXI boilers essntially a Combi and Unvented cylinder all in one?

 

[ajrobb]

If you want a combi-boiler to deliver 20 litre/min at 38°C with a 5°C winter feed temperature, you'll need 46 kW. Given your high mains water pressure, an unvented cylinder ought to be OK though. At 60°C storage temperature, you'll be drawing 12 litre/min from the cylinder mixed with 8 litre/min cold at 5°C to get 38°C. A 200 litre cylinder will run cold after less than 15 minutes without boiler heat. With a 23 kW boiler and effective heat exchange (just grabbed half of 46 kW for argument's sake), you can double that to less than 30 minutes.

 

[Krobar]

Hi AJRobb,

The brochure the plumber gave me mentions Max DHW Flow rate = 36ltr/[email protected] for the Ultrapower. Is that 36lr/min of 65C water!

For example in theory could the 170litre ultrapower with a mixing shower provide 60litres a minute of warm water for about 6mins?

 

[ajrobb]

EDIT: that is 170 litres storage and 31 kW output. At 65°C storage, you'll get more than 5 litres of shower for 3 litres of stored hot water, or about 15 minutes. Add the 31 kW heating and you'll more than double that. You should get at least 30 minutes of shower.

 

[Krobar]

I'm pretty sure it is 170L, "Volume of DHW produced 170L". Its called a 170SXI too but one of the diagrams comparing it to a conventional coil store show the Ultrapower as 120L.

 

[Krobar]

EDIT: that is 170 litres storage and 31 kW output. At 65°C storage, you'll get more than 5 litres of shower for 3 litres of stored hot water, or about 15 minutes. Add the 31 kW heating and you'll more than double that. You should get at least 30 minutes of shower.

Could it be setup to provide a higher flow shower for less time?

I'm a bit confused on how you feed these 400mm big shower heads. They say min of 2 bar pressure but what about flow?

 

[ajrobb]

Looking more carefully, 170 litres of hot water is produced at 36 litres/min. This is a combination of 67% storage and 33% heating. Heating produces up to 12.5 lirtres/min at 35°C rise. The storage is probably about 100 litres. With the 170 sxi you should get about 20 minutes of shower at 20 litres/min.

 

[Krobar]

Looking more carefully, 170 litres of hot water is produced at 36 litres/min. This is a combination of 67% storage and 33% heating. Heating produces up to 12.5 lirtres/min at 35°C rise. The storage is probably about 100 litres. With the 170 sxi you should get about 12 minutes of shower at 20 litres/min.

Thanks AJRobb, that is helpful. Looking at shower heads Hansgrohe 300mm heads are for 22ltr/min at 3bar, would this likely be a good match? Is 3bar and 22ltr/min realistic from a 170SXI?

Edit: Just did some reading up, it seems the pressure in the cylinder will rely on my mains water pressure. So assuming 3bar+ pressure I assume a 3-400mm shower head would be a good match.

 

[ajrobb]

If you have fixed on the type of shower head, I suggest hooking it up in your bathroom and running cold water through it to measure the flow rate. You say you have excellent water pressure but it sounds like that was measured statically. It is possible that your mains feed could be restricted and pressure might drop off rapidly with increasing flow rate. Once you've established that the mains can give you a good shower, you should be safe to choose your boiler/cylinder. In the end, it is the installer that has to ensure the system is adequate.

It is typical to regulate unvented hot water cylinders to 3 bar.

 

[ColinJacobson]

A neighbour installed an Alpha Flow Smart. I was impressed. It is a combi assisted by a very small and neat, white, thermal store cylinder. The picture shows how small the cylinder is. The cylinder pre-heats the hot water. He never had space for a big cylinder. He can switch off the thermal store cylinder and just use the combi. It is cheap to run as he does not have to heat a whole cylinder each time he needs hot water. He tends to use the cylinder for baths or when they have two showers on the go. He does use the time clock, just switching on the cylinder when needed as it heats up in about 5 minutes. He said by the time he has switched on and got undressed the bath can be filled very quickly, then a shower in the en-suite can be used straight away. He said he has never run out of hot water and can't speak highly enough of it. His bills are way down on running the big old cylinder he had. He never bought the energy saving box as he never had room.

From their web site......
3 year guarantee
18 litres/minute at 50°C and above
No need for G3 registration (whatever that is)
No unvented kit required
Overcomes flow rate issues associated with combi's
Reheat time of 6-7 minutes

The Alpha web site shows two sizes of cylinder with both still small. There is some electric immersion thing as an extra. I never went into that.

http://www.alpha-innovation.co.uk/products/FlowSmart/FlowSmart/991603208

 

[Krobar]

Thanks for the reponses everyone.

Hi Colin,

I think the products you list are more or less just the tank half of the Ultrapower boiler I've been looking at. Since my current boiler is 18 years old and not too efficient I think I should probably just replace the whole unit with an Ultra Power.

The plumber said there is easily enough mains pressure to get 3bar on 3/4" piping out of the boiler tank. He said I will need a seperate cold water feed to the bathroom which will allow a 3/4" shower mixer to run without pressure loss. Does this all sound sensible?

One other thing, with standard depth shower trays do I need to worry about them getting rid of the water fast enough?

I checked the plumber is Gas Safe and according to his ID number does Unvented tanks too.

 

[ColinJacobson]

Thanks for the reponses everyone.

Hi Colin,

I think the products you list are more or less just the tank half of the Ultrapower boiler I've been looking at. Since my current boiler is 18 years old and not too efficient I think I should probably just replace the whole unit with an Ultra Power.

The plumber said there is easily enough mains pressure to get 3bar on 3/4" piping out of the boiler tank. He said I will need a seperate cold water feed to the bathroom which will allow a 3/4" shower mixer to run without pressure loss. Does this all sound sensible?

One other thing, with standard depth shower trays do I need to worry about them getting rid of the water fast enough?

I checked the plumber is Gas Safe and according to his ID number does Unvented tanks too.

Krobar, the Ultrapower has an unvented pressurised cylinder inside a combi. I looked. You cannot switch out the cylinder, so it is always hot.

The Alpha is thermal store which is not a pressurised cylinder. The thermal store (a very small cylinder), can be switched out with only the combi running. The thermal store boosts the hot water output of the combi when you need it.

He said all it needs is a push button timer set to maybe one hour. Screwfix do them, setttable from 2 mins to 2 hours. The combi always gives hot water like a normal combi and can do a shower. When he needs a boost, he said he could just hit the botton. Then it will stay heated up only for an hour or whatever the timer is set to. 1/2 hours seems good to me. He said it recovers so fast, within minites, that a timeclock is unnecessary, just switch on when you need the hot water boost. This saves a ton of money. He leaves it off most of the timer in summer as they use showers. It is used for baths or when two showers are used. They all know that when one shower is being used and you want a shower, just hit the button and two showers can be had immediately.

Apha has a valve that drops the water flow in winter, so you don't have full flow warm water.

He, and I, are greatly impressed. His builder recommended it when he was building the extensionn as space saving was the prime concern. With gas bills rising it can only be a good thing to save money. His gas bills dropped like a stone after fitting.