Increasing the volume of available hotwater

[Richard Savage]

I have a very powerful twin impeller shower pump made by Techflow. Great bit of kit except that my h/w tank only holds sufficient water for one pumped shower.

Is it feasible to add a second h/w tank? I know someone who has one boiler heating the water in dedicated tanks for each bathroom but I want to increase to overall volume of h/w that is available.

To make life less simple (perhaps) the second tank would probably be on a different floor from the main tank.

TIA Richard

[David]

Sounds very complicated, but even if do-able, surely logic dictates that it's bound to be less economical heating up two tanks rather one. If you are going to all the effort and expense of installing a new tank, why not simply make sure it's big enough for your needs on its own, and dump the original one?

David

[L Reid]

I take it replacing your current cylinder with a larger one is out of the question?

[N. Thornton]

Yes its feasible. A much easier solution is to increase the temp setting on your HW cylinder. Upping it from 60C to 95C would give you much more HW effectively, since you will be using the hotter water at a lower rate.

There are 2 downsides:

1. faster scaling in hard water areas reduces electric heater element life.
2. If someone was determined they could get water a 95C out of the tap

- and thats hot!

These problems are resolvable, if they are a problem in your case.

Regards, NT

[IMM]

Assuming a gas biler set to max (82C).

In hard water areas a phosphor descaler should be in the water anyhow. This will solve that problem.

Install a blending valve on the DHW draw-off to blend the water down from

80C to 45-50C

For the cost of a blending valve and ramping the cylinder stat to 80C, all is solved. The blending valve prevents scalding too (user adjustable). Are the showers to be used simultaneously? Or is the re-heat the problem?

and Screwfix have them.

[Richard Savage]

Replacing the existing cylinder is not an option as the former airing cupboard that it shares with the pressure vessel (no C/H header tank) is a veritable rats nest of pipes.

The pump is a Techflow QT80 and the water temperature is specified as:

1.The temperature of the hot water supply MUST NOT exceed 70°c at the pump inlet. A cylinder stat. MUST be fitted to provide adequate temperature control and set to a MAXIMUM temperature of 65°c. However, other appliances and fittings installed on the domestic water system may only be rated up to 65°c and therefore the system temperature should be reduced accordingly.

The boiler is set to maximum and the cylinder stat to 70 deg C even though the pump is less than 2' from the tank.

I don't follow the point about the expense of heating two tanks rather than one (twice).

From the above you can understand why I really think that a second tank is the only option.

BTW the current system was installed less than 3 years ago.

Richard

[IMM]

Do what I suggested. Install a blending valve that delivers whatever temp you want and store the water at 80C (set the cylinder stat to 80C). Set the boiler to max. You "will" increase the hot water available, but not the draw-off temp, as this you set yourself at the blending valve. see:

the Screwfix catalogue.

[N. Thornton]

Cant say I ever worried too much about the high hot temp, but yes a blend valve and, if electric heating, an alloy element would be a good idea.

Regards, NT

[Richard Savage]

Sorry IMM,

I didn't see your question above. The problem is re-heat time. There is only one shower supplied by the pump.

Richard

[Richard Savage]

Ah! Picture of light dawning!

You mean run the tank stat at the highest setting and use the blending valve to introduce cold water into the (scalding) supply to the pump - yes?

Sounds like just the ticket.

Thanks

Richard

[IMM]

Cylinder stat, not tank. Yes, you got it. Keep the cylinder stat a few degrees belwo the boiuers stat, otherwise it will not switch off the bliler when hot.

It will work, and you will get most of the time a perfectly blended temperature of hot water. Adjustable by you. Try 50C at the blending valve. The kitchen tap is the one that requires the hottest water, 55c recommended. But some find this too hot.

[IMM]

Sounds as if a normal British Standard cylinder was installed. A quick recovery cylinder using a priority system that diverts all the boilers heat to the cylinder would re-heat very quick. As you draw off water it would be also be re-heating very fast.

Using quick recovery cylinders, and a DHW priority system, the cylinder size can be made smaller. Or replacing size for size the cylinder will effectively be made larger. Raise the cylinder storage temperature, and larger again.

From Albion:

A practical example is to compare the hot water available from a CF45 [45 litre capacity quick recovery] against that from a standard indirect 900 x

450mm cylinder [120 litres capacity] . Using a 15Kw [51,180 Btus/hr] boiler the standard cylinder will deliver approximately 175 litres of hot water per hour (based on 40minutes recovery). The Superduty CF45 will produce approximately 340 litres in these circumstances. (8 minutes recovery).

[Richard Savage]

Wow!!

I may ask my plumber (who installed the original system) about replacing my cyclinder at the same time, if feasible.

Thanks mucho for the very useful info.

Richard