Plus ca change . . Heating question - long

[Nicknoxx]

A few days ago I asked a fairly unstructured question about the Keston Duet Boiler. Now I haven't visited uk.d-i-y for a few years and didn't quite get the response I'd hoped for. One answer from Doctor Drivel who I assume is a re-incarnation of IMM given the arrogant but basically unhelpful posting style and two valuable (if conflicting) replies (thanks Andrew and Tony). So here is my detailed situation for your perusal.

I'm about to buy a grade 2 listed property with a dead heating boiler. At present the house has one bathroom but it is my intention, subject to listed building consent and building regs, to install another, both with showers and baths.

I would like to do as much of the installation as possible and have installed complete heating systems before so feel fairly competent. I have a tame Corgi man to do the gas.

Now, to supply two simultaneous showers I either need a very large combi (I'm thinking Worcester Greenstar High Flow 440) or an unvented system as there is no loft space for a header tank, hence the Keston thought as it looks easy to install. I'll be involving the building control anyway so they could check the unvented system for me.

The existing boiler is flued through an old chimney stack and I'd like to keep this arrangement as a new flue will require both planning and listed building consent which means I need a conventionally flued boiler, doesn't it?

Finally the boiler will be sited in a utility room which is, effectively, underground (the house is built into a hillside and the kitchen and utility form the back wall) which might make tundish discharge and condensate drain problematic.

There is a sink and loo in the room already.

Budget £2000

helpful advice and comments greatly appreciated.

[The Natural Philosopher]

Correct on Drivel.

Mmm. I would go unvented personally, but you obviously understand the issues.

Not sure a balanced flue does,but given the location of your utility room..a conventionally flued boiler would seem to fit the bill.

Not sure that isn't simply a question of fitting a different adapter plate, on many units.

The tundish on mine is not associated with the boiler, but with the tank, which, in my case is in the loft. A very long pipe runs from that to outside.. check with building control..it may be possible to go straight into any convenient drain.

You will need SOME form of drain in the utility room whatever you do, or it loses its utility..if the kitchen is next door it can't be that hard.

If you have room I would go mains pressure personally, because its so much nicer, and your boiler gets smaller, but of course the tank is not cheap. Or small. But it can be put anywhere really.

With a sink and a loo in the utility room (strange utility room) you do at least have drainage you can tap into.

[David Hansen]

On Tue, 23 Jan 2007 20:35:06 +0000 someone who may be Nicknoxx wrote this:-

You have left out a thermal store. Some of these have small header tanks built into the top of the store. With one of these you get instantly heated mains pressure hot water, but not the installation and ongoing hassle of a pressure vessel full of hot water.

[John Rumm]

IIRC there have been a few posts here in the past slating these for reliability problems - but no personal experiance, so YMMV.

I think you need to establish the answers to some basic questions first before worrying about trying to answer them...

Things like, two showers, but what do you consider to be a good shower? Its a personal preferance thing. If you want body jets and drencher heads it is a very different requirement to an "ordinary" shower.

For example, my 15 lpm combi will feed both our showers at once - but only just, and only with a loss pressure / flow performance on each.

Next thing is what is the mains flow rate like? Until you know this you can't really make sensible decisions about how to proceed. No good having a on demand heating system that can give you 30lpm if the main can only do 15 etc.

Do you want to run baths at the same time as a shower is in use? A system that can provide two showers on demand would probably not cope with bath filling at the same time as a shower.

Not really. Many boilers can support a resaonable length of coaxial balanced flue. You can also go for those that support separating them out into two plastic pipes etc.

Don't know what specific regulations apply to tundish discharge, but a pump can be used for the condensate.

They presumably have some form of drain that could be used of the condensate at least.

[Nicknoxx]

As I understand it, and correct me if I'm wrong, the disadvantage of a system like this is that it provides a decent flow rate for a while but at some point the tank is emptied and the flow rate reduces to the point where you can't run two showers simultaneously.

[Phil L]

Why not just install electric showers and install a normal boiler - you won't be able to run 2 showers simoultaneously whichever option you choose, unless the mains pressure is extremely high, but considering the house is old, I'm guessing the water main is too?

[Roger Mills]

I don't think that's right. The flow rate is determined by how fast the mains supply can force water through the heat exchanger and out of the shower head. That doesn't change as the heat in the store gets used up - but the temperature may drop a bit. However, as soon as the store starts to cool, the boiler will fire up and heat it up again.

[Nicknoxx]

Ok, I'll look into it, Thanks

[Nicknoxx]

But I thought that Worcester boiler had a good reputation for reliability, or is it just the large floor standing combis that have problems?

My 12lpm combi can only cope with one shower so lets say that 20lpm will be enough for two.

Good point, Obviously I won't know till I move but the house it low lying unlike my present one which is at the top of the hill so pressure shouldn't be a problem. I'll investigate two systems, one assuming there's a decent flow rate and one assuming the isn't.

No, two simultaneous draw-offs should be enough.

But how will I get a coaxial flue up the old chimney. Are flexible ones available? If I use a traditional flue can I draw air from inside the house?

Thanks.

[David Hansen]

On Tue, 23 Jan 2007 21:45:13 +0000 someone who may be Nicknoxx wrote this:-

The flow rate of hot water from a thermal store will not vary, unless mains pressure varies.

As hot water is drawn off the temperature of the lower part of the store will be reduced to the point where the boiler comes on to recharge the store. However, hot water will still come out of the coil because the top of the store is still hot. Provided that the store/boiler system is suitably designed, sized and the controls are set up properly the store will be recharged long before hot water ceases to come out of the coil. With those provisos hot water can be drawn off indefinitely.

The flow rate will not reduce, unless the mains water pressure reduces. The temperature of the hot water will not reduce (other then by a minimal amount), provided the points above are complied with. It should be possible to run two showers indefinitely, with the store being recharged automatically as necessary. It will probably hardly be tickled. Even running a shower simultaneously with people taking one bath after another will be no problem if the points above are noted.

[David Hansen]

On Tue, 23 Jan 2007 22:05:44 GMT someone who may be "Phil L" wrote this:-

If there is enough water to run two electric showers then there is enough mains water to run two of any other type of shower.

[Dave Plowman (News)]

You'd need a *very* poor mains flow rate if an electric shower can heat it to the required temp at maximum flow - they're all under 10 Kw. Much less than even the smallest cheapest combi.

[Roger Mills]

Well, sort of! Assuming adequate mains, the ultimate flow rate will be determined by how fast the elements can heat the water. If you have an alternative system (e.g. heat store) which can generate hot water faster - and give a potentially more pleasing shower - mains supply may then become the limiting factor.

[David Hansen]

On Wed, 24 Jan 2007 09:50:33 -0000 someone who may be "Roger Mills" wrote this:-

It may become the limiting factor. However, if people are happy with the flow rate of an electric shower and two of them can be supported by the available flow then people can get the same thing from other forms of heating. They may want more, in which case as you say the mains may become the limiting factor.

[Doctor Drivel]

He wants to fit it himself. He can't fit an unvented cylinder and they cost from £60 to £100 a year to have serviced. Heat bank is the better option.

[Doctor Drivel]

What response did you want? You got a few comprehensive ones from me. At least say thanks.

Well that precludes an unvented cylinder then.

They may not and farm it out to a local BBA approved plumber - and you pay. Check this.

No. You need a boiler that has a plastic twin flued system. The pipe(s) can be threaded up the chimney. The exhaust can go up with the air intake or can terminate elsewhere (on the same side of the building.).

If there is a kitchen then there is a drain. The Atmos boiler does not require a condensate pipe. The DPS Pandora DHW only heat bank does not require an overflow of any sort.

An Atmos and a Pandora is worth looking at. Not sure if the Atmos can have extended plastic flue pipes. Give them a ring:

Alternatively: One alternative for the poster is have a Rinnai or Andrews multi-point two bathroom water heater. They have models that can go outside on the wall - they don't have condesnsate drains. This will deliver the DHW flows no problem. The Rinnai is the largest selling water heater in the world - made in Japan and a class act. They have a remote waterproof temperature controller. You can be in the bath or shower and set the temperature. The Andrews is also made I think in Japan by Rinnai or a competitor.

The Rinnai or Andrews costs less than an unvented cylinder and never runs out of hot water. Great for body jet showers.

Fit a CH system boiler sized to suit doing CH only. The Keston Uses cheap plastic drain pipe that can be run up the chimney. A condensate pump can be fitted in the kick space of units and the condensate pumped to a far off drain.

A problem will be that if both are on at the same time the gas meter will be too small in theory; in practice they have an overload. The way around this is have a flow switch on the cold feed to the Rinnai. Run the CH boiler room stat circuit through this and the room stat. When the Rinnai demands hot water the CH is turned off. No cylinders, tanks and two girls can stay in the showers for ever more and not run out of hot water.

Look at Rinnai and Andrews:

So to bottom line:

1. Atmos boiler if the flue can be extended and a Pandora heat bank.
2. Atmos boiler if the flue can be extended and a Rinnai high flow multi-point fitted outside.
3. Keston boiler with a condensate drain pump and a Pandora heat bank.
4. Keston boiler with a condensate drain pump and a Rinnai high flow multi-point fitted outside.

3 and 4 will be around £2K. Not sure about the Atmos with a flue extension (if feasible of course)

[Doctor Drivel]

He can always fit a cold water accumulator to give high cold pressures and volume.

[Nicknoxx]

True but you make statements like the one below which are not true (ie it IS POSSIBLE to do a DIY unvented installation if you get it checked by a BCO) and this undermines the rest of your advice.

snip I'll be involving the building

See, even you agree it is possible

Are you sure about this?

Interesting, thanks

The way

[The Natural Philosopher]

WHY are you responding to Drivel?

Sometimes its good sport, but attempting to correct his strange beliefs has proved impossible.

Best ignored.

[Doctor Drivel]

I told you many will not do it and refer it to a BBA approved fitter - and you pay. BCOs are trained surveyors, not experts in plumbing and gas. I was reading the IOP were getting onto the BCOs. and BCOs don't want the responsibility; if one explodes and they siogned it off?

The BCOs want little to do with services, as they have enough to do with the structure and fabric. If it is approved fitting or Part P they farm it away. You may get one to pass the unvented and in theory he can, but you will be lucky.

I know "exactly" what I am on about.

It is crazy as you can be in a full body jet shower for ever. Try that with a cylinder. They work well, very well. They are also cost effective and need not be inside the house. If the boiler is down the multi-point works. Rinnai are the largest selling multi-points in the world; a class act.

If space is a problem I would go for the Rinnai.