Pump in loft between cold tank and hot tank?

[David Hearn]

We have mains pressure cold water to all taps/outlets (inc toilet), and low pressure hot water. We live in a 1930's semi, so cold tank (only used for hot water header) is situated in loft and we therefore have very little hot water pressure. We have a single upstairs bathroom and single kitchen. No other hot water outlets. Mains pressure is pretty good (I've no complaints).

We need to replace our electric shower sometime, and due to a number of reasons, are considering adding a pump to the existing hot water feed. This would improve bath filling time, and (hopefully) could be used with a mixer shower using cold mains + pumped hot water. Is a mixer shower with mains cold + pumped hot likely to be successful? We currently have a 8.5kW electric shower which does an adequate, but not particularly enjoyable job. So, not looking for amazing shower performance, but a better experience than present.

It seems that the normal place to plumb a whole house/shower pump appears to be on the output of the hot tank, and at the same level as the hot water tank (e.g. 1st floor airing cupboard floor). I've seen some manufacturers which say it can be fitted in the loft, but still must be fitted to the output of the hot tank - and may require special tapping off the tank in this situation (believe to ensure no air drawn into pump), and a particular pipework layout between tank and pump. Our airing cupboard doesn't really have any space for a pump and associated plumbing.

I'm interested in whether it's possible to do it differently and add a pump on the output from the cold tank before it feeds onto the hot tank. Therefore the existing hot tank plumbing to rest of house could be used, a far easier location for the pump (no space in airing cupboard) and wouldn't require special tapping on the hot tank as water could be coming from bottom of cold tank (rather than top of hot tank).

Does this sound possible? Would a special pump be required? Do any manufacturers support use like this?

Thanks

David

[dennis]

The pressure would probably burst the tank!!!!!!!

You would have to fit a new mains pressure tank to take the pressure and then you may as well fed it from the mains and do away with the pump.

Mains pressure hot water tanks are not cheap. They start at several hundred pounds + fitting + testing.

Stick with the normal twin impeller pump for the shower and maybe the bath filler only about £150 and a lot safer.

[newshound]

I don't see why a mixer shower designed for mains pressure should not cope with mains cold and pumped hot.

BUT, you must not be able to pump anything back into the cold mains; water regs are strict about this, in principle a non return valve provides protection, but you need advice from an expert.

Also, the hot pump needs to be on the OUTLET of the hot tank, for the reasons given by other posters.

I have pumped DHW to taps from a conventional hot tank. There's a mixer tap at the kitchen but the design prevents cross-contamination.

[David Hearn]

I can immediately see the problem now with my idea!

Thanks

D

[BigWallop]

Could you run a new pipe from the cold water tank, along with existing hot feed, to the pump.

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[David Hearn]

The two problems with putting pump next to hot tank I see is that we don't have room for the pump next to the tank in the airing cupboard (there is space, but that space is used for something else that we don't have space to fit anywhere else!), even if we did have space, I'm not sure about the noise it would make (hot tank is in a child's bedroom and showers/baths often take place when they're asleep). Unless you can get very quiet ones, I'm not sure I'd like to put it there. At least in the loft, there's insulation which might help quieten it?

The problem with putting the pump in the loft, fed correctly from the hot tank outlet (and following a manufacturer's requirements for pump in loft) is that one requirement is that the must be water drawn off from a new tapping cut and fitted into the side (so cannot use one of the various flanges) - I don't particularly want to modify our tank in that way.

Thanks

D

[BartC]

I remember buying a house where the shower unit over the bath was actually a pumped unit, fed from an extra outlet from the side of the hot water cylinder (and using a 15mm pipe).

But it was faulty, so I've no idea how well it worked. Or whether you can still buy them.

Anyway, it shows they can be anywhere.

[Pete Shew]

[John Rumm]

They can still make some noise even in a loft... but probably not the sort of noise that will keep a kid awake if they are used to the sound of tanks refilling etc.

One option is a pumped shower there the pump is actually in the shower unit. Aqulisa make some of these - they are fed from a low voltage supply that can be outside of the bathroom.

A normal pump under the bath is another option.

Also you could look at a venturi shower. These are designed to work with mains cold and low pressure hot. They use the pressure of the mains to drive a turbine which in turn pumps the hot.

Again there are options here. If you are talking about relatively low power pumps (say less than 2 bar) then you may be able to draw the hot from the existing feed without any difficulty. (I have fitted a Stuart Turner 1.8 bar pump to a tank with no flange in the past and it worked well[1]).

The next option is a Surrey or Warwix flange. These fit into the top hole of the tank and hence require no modifications to it. (its also easy to make a suitable flange)

[1] Ensure the side of the tee is used for the shower, and route the pipe around and downwards for a few feet before going any other direction.

[ARWadsworth]

Bloody hell. Where have you been Wallop?

[NT]

Before adding the pump, you could turn the HW temp up high and see if that gives enough heat/flow to the shower. Going from 60 to 90 changes the delta T from 50 to 80, so over 50% more heat delivered to the shower.

NT

[Grimly Curmudgeon]

Sure, it's possible, but you'd flood your loft with the vent pipe. You could _and it's only a could_ fit a 1 or 2Bar pressure relief valve on the vent pipe and block it off. I'd not want to be living next door to you, though.

[Tim..]

No, no no.

Fit a pressurized cylinder eg Megaflow type. Get rid of the header tank...

Tim..