ripping out an old gravity fed HW tank and fitting a thermal store?

[speculatrix]

thanks for your time for reading this...

** The situation

There's a reasonably good gas Baxi back boiler that gravity-feeds a very old hot water tank in an airing cupboard on the landing, header and expansion tanks directly above in the loft. Central heating controller is a Honeywell 7 day multi-on-offs electronic timer. Even in winter, the central heating works well whilst also getting the tank hot, so the boiler seems sufficient.

The mains water pressure is fair to good, but only moderate flow.. water pressure in the area is often a problem, I guess this is why the header tank was originally installed, but also the mains into the house is just 15mm, and it would be very hard to upgrade it.

The boiler has a companion Baxi enclosed flame gas fire which is quite decent, hence keeping the same boiler and fire would be preferred.

Residents are likely to be here for another 9 years and want to use high quality low maintenance products.


** the problems

Internal hot water flow is ok for a bath, pressure just so-so for a shower, replacing some of the feeds with bigger bore would help.

The hot water recovery time is quite poor, probably because the heat exchanger in the tank is scaled up and being purely gravity fed the boiler cycles a lot. So the plan is to add a Y valve and possibly up-rate the pump.

The boiler cycles a lot, and gas bills are quite high for a semi-detached.


** The project

Apart from the boiler and the pump, everything is over 30 years old, so noone's going to be crying when things are ripped out! OK, the heating controller is only maybe 20+ years old!!

The project is to replace the HW tank, with a thermal store being favoured, with heat provided by existing boiler, and fit solar hot water system too. If pressure/flow not so good, a booster pump is possible.

Having done a fair bit of reading, the ACV product SLME 200 seems like a high quality unit for this. Or, possibly the Navitron Thermal Store with additional coils; being a more local company seems an advantage.


So
- remove old tank
- inspect/replace/upgrade pipes to check for corrosion, and suitable bore
- fit new tank with pipes to loft for the solar hot water system
- fit Y valve and change the controller
- fit solar HW system possibly as a separate phase?

this is one of those projects which seems fairly straight-forward but I reckon there could be some problems lurking meaning a contingency of an extra two days?


Any thoughts would be gratefully considered.

thanks again for your time
Paul

 

[Whyme]

If your going to that trouble why on earth would you keep the un efficient bbu ??

 

[speculatrix]

If your going to that trouble why on earth would you keep the un efficient bbu ??

Long term, yes, new boiler, but big big job.

The layout of the house would make it quite difficult to put the boiler somewhere else, and also be a significant problem in living room where the baxi boiler & fire are.

 

[Chalked]

Don't understand! After you have researched so much, you then decide to keep a back boiler,that is at best 60% efficient?

 

[IDCHAPPY]

The boys are bang on, rip out the bbu and stick in a 89% Efficient modern boiler

 

[voivod]

Ismadness not to upgrade....will cost more to do later...and more torun now

 

[Neil K]

Get rid of that poxy Baxi for starters

 

[southcoastboile]

You might be able to put the new boiler in the airing cupboard.

pointless upgrading the rest if the system without doing the bb.

 

[speculatrix]

I hear you. house is a chalet style so upstairs is basically the root with dormer windows; loft is narrow but tall.

With a bit of building work could fit something in the space of the back boiler, it's basically been partly bricked in. There's a double-skin flue that goes up through a protective shaft then through loft to the roof; getting a balanced flue to the outside wall would be an interesting project.

Hot water tank is in airing cupboard on landing, fills most of the space. I guess a new boiler could go into the roof space, there is a riser with the SVP plus cold feed, could get gas feed off that... but getting it up there would be a hell of a job as the loft hatch is just about big enough for a medium fat man, probably would mean ripping out part of the ceiling and then making good.

hmm. lots of options but many practical problems.

You'd have to save a hell of a lot of gas to recover the cost!

 

[southcoastboile]

Can't u put it above the cylinder or do away with the solar idea and get a combi.

if you put it in the loft it will have to have a hand rail, lighting etc or the manufacturers won't touch it under warranty and it doesn't sound like you have the space.

 

[speculatrix]

Can't u put it above the cylinder or do away with the solar idea and get a combi.

if you put it in the loft it will have to have a hand rail, lighting etc or the manufacturers won't touch it under warranty and it doesn't sound like you have the space.

yes, a boiler in the loft would have to go onto the gable wall which is some way from the hatch, and there's a raised platform for the HW/CH expansion tank, and a fairly large water tank. Lots of tripping hazards, moving the tanks can be solved though. There is a light.

The airing cupboard is raised about 2 feet above the floor, because it's above the first few stairsr, so is kind of partly hanging in the air, the underside/ceiling is partly sloping as the stairs rise. I don't think there'd be room in there for a boiler and the HW tank.

I suppose a combi could be put in there, but then the water pressure/flow issue comes back.

If I was starting from scratch, and the house was a shell, it'd be a lot easier!

 

[Rickster123]

I love a baxi bbu. Inefficient yes, but those things will out live most of us if maintained correctly. Modern boilers are fantastically efficient but if you have one ten years then it's lasted well.

 

[PhoenixServices]

Just to throw another option in. Couldn't you fit a new condensing back boiler. If you can get the condense out somewhere.

 

[speculatrix]

having had more time to ponder this, there is one possible place where fitting a condensing boiler is possible, it would be in the living room in the alcove to the right of the existing "chimney" breast (where the baxi lives). It could be partly boxed in so as to look like part of a book case.
It's right next to the outside wall, and not a big stretch from the existing bbu.

the more I think about it, the more I like it.

BTW, I talked to Craig at ACV. He explained that the anti-scaling feature of their SLME relies on the tank flexing. In a harder water area like Cambridge with a vented HW system, that wouldn't happen, scale would build up, and shorten the life of the tank.

 

[Ermintrude]

Water softner

 

[Chalked]

having had more time to ponder this, there is one possible place where fitting a condensing boiler is possible, it would be in the living room in the alcove to the right of the existing "chimney" breast (where the baxi lives). It could be partly boxed in so as to look like part of a book case.
It's right next to the outside wall, and not a big stretch from the existing bbu.

the more I think about it, the more I like it.

BTW, I talked to Craig at ACV. He explained that the anti-scaling feature of their SLME relies on the tank flexing. In a harder water area like Cambridge with a vented HW system, that wouldn't happen, scale would build up, and shorten the life of the tank.

that isn't stopping scale build up. It's just stopping it adhering to the sides. It will still be turning into flakes and sinking to the bottom.

 

[Ermintrude]

The scale is flaked to keep heat transfer coefficients .