Best solution for a 2-bath + cloakroom flat

[Amateur99]

Sorry if this repeats earlier questions, but have searched and found no answers.

Have just bought a new flat, top two floors of a 4-storey (inc basement) period conversion, which will have:

1. Ensuite drench-shower room with WC (2nd floor)
2. Family bathroom with shower and WC (2nd floor)
3. Cloakroom with WC (1st floor)

I see that these forums contain some fairly vitriolic debate on the relative merits of vented and unvented thermal stores, which has left me utterly confused on that score, and I don't want to reopen that debate.

My problem is that I want to be able to run two showers at the same time, in theory at least. I know from my current flat that a single combi boiler won't cope.

My friend tells me that he has installed a combi boiler with double the required capacity, and that as a result he is able to run two showers at the same time. Is this a sensible solution? From what I've read elsewhere on these forums, it sounds as though that's an inefficient approach that will lead to higher bills, though I don't quite see why as you'll still only ever be heating the water you actually use.

My second question is whether a combi is much more efficient than a heat store. Both the unvented (megaflo-style) solution and the vented thermal store (eg Gledhill Gulfstream) seem inefficient in principle as you are heating a large volume of water and then just leaving it there, or keeping it hot. On the other hand, apparently it's much better to heat a body of water in a single burn than to have the boiler coming on and off to heat water as required.

Can anybody offer a comparison of the efficiency (in terms of running costs) of combi vs thermal store? Can you quantify it (ie roughly how much will I save using one rather than the other)?

Thanks very much in advance for any help you can offer - I'm a bit lost with all this!

 

[gas4you]

If money is no problem then I would go for the Vaillant Unistor cyliner and Ecotec Plus system boiler connected via a VR65 control centre.

A Vaillant Ecotec Plus 937 may just cope with 2 showers but certainly not a bath and shower run at the same time.

Have you considered the option of a combi supplying one bathroom and an electric shower supplying the other?

 

[Amateur99]

Thanks, Dave - I hadn't considered an electric shower, but I did consider two combi boilers (eg two of the 937s). Is that a sensible solution?

Is the Unistor an unvented mains-pressure system like the Magaflo (ie I need G3 certified installer and BC approval, plus annual service, and it's only worth doing if the mains pressure exceeds a certain minimum, which I think from memory is about 2.3 bar)?

 

[Doctor Drivel]

Sorry if this repeats earlier questions, but have searched and found no answers.

Have just bought a new flat, top two floors of a 4-storey (inc basement) period conversion, which will have:

1. Ensuite drench-shower room with WC (2nd floor)
2. Family bathroom with shower and WC (2nd floor)
3. Cloakroom with WC (1st floor)

I see that these forums contain some fairly vitriolic debate on the relative merits of vented and unvented thermal stores, which has left me utterly confused on that score, and I don't want to reopen that debate.

My problem is that I want to be able to run two showers at the same time, in theory at least. I know from my current flat that a single combi boiler won't cope.

You may need stored water of some kind, but not necessarily. But read on...

My friend tells me that he has installed a combi boiler with double the required capacity, and that as a result he is able to run two showers at the same time. Is this a sensible solution?

For normal showers, yes. You have a drencher!!! If this and the other shower are on together the drencher will be cut back in flow. That may not be a big problem for you. Or do you need a drencher all the time irrespective? They are very expensive in water and heat to run.

My second question is whether a combi is much more efficient than a heat store. Both the unvented (megaflo-style) solution and the vented thermal store (eg Gledhill Gulfstream) seem inefficient in principle as you are heating a large volume of water and then just leaving it there, or keeping it hot. On the other hand, apparently it's much better to heat a body of water in a single burn than to have the boiler coming on and off to heat water as required.

Modern combis are efficient that is certain. However stored water in highly insulated cylinders is not that much of a problem.

Can anybody offer a comparison of the efficiency (in terms of running costs) of combi vs thermal store? Can you quantify it (ie roughly how much will I save using one rather than the other)?

Not much in it. Your problem is getting the best compact solution for your DHW needs.

Space? How much of it do you have? The ACV HeatMaster is a one-box floor mounted class act and will do what you need and more and is very efficient indeed. A hybrid of thermal store and unvented cylinder. The Atmos Multi is another that will do what you need, Then the Gledhill Gulfstream too. All floor mounted.

Another alternative is to have two Atmos Intercombi wall mounted boilers, One does one floor of the place in CH, on the other. One does one bathroom, one the other. Combine the DHW outlets for the baths and drencher shower using two check valves. Total output is over 24 litres/minute. This is a space saving cost effective solution, also gives backup too if one boiler is down. Also you NEVER run out of hot water, as you will with an unvented cylinder so you can stay in the drencher all day. Atmos are high quality. Total cost of two boilers is under £2,000 and no zone valves and control stuff either. Simple.

A quality system boiler and large unvented cylinder to cope with two showers and one a drencher, is around £2,500 minimum, and that is not costing in CH zoning - zoning cheap to run as you are not heating parts of the house you are not occupying.

 

[Doctor Drivel]

Thanks, Dave - I hadn't considered an electric shower,

Don't. They are made by Satan himself.

but I did consider two combi boilers (eg two of the 937s). Is that a sensible solution?

See my post re: two combis

Is the Unistor an unvented mains-pressure system like the Magaflo (ie I need G3 certified installer and BC approval, plus annual service, and it's only worth doing if the mains pressure exceeds a certain minimum, which I think from memory is about 2.3 bar)?

Avoid unvented cylinders if you can. The Unistore is unvented. Check out your mains pressure and flow. This can be improved by a new larger bore, full bore stoptap and a dedicated 22mm pipe to the combi/cylinder.

 

[Agile]

Any combi or unvented cylinders will need a very good mains flow into the property.

The mains pressure is irrelevant, its the dynamic pressure thats relevant, as a minimum 20 li/min @ 1 Bar.

However you dont say the consumption of your "drencher" is. If its as bad as it sounds then you might have to have stored water.

One I saw on the net wanted 12 li/min at 55 C which is more than all but the largest boilers will give. there can be another problem because they are not designed to give DHW at such a high temperature. Those kinds of showers are expected to be supplied from stored water.

There is little difference in efficiency between a combi and stored water in a normal house.

Tony

 

[Nixt]

See my post re: two combis

Which one?

 

[Amateur99]

Thanks all for suggestions so far - perhaps by saying "drench" shower I am being untechnical - I was thinking of one of the large round-headed showers, but have not chosen the model or checked the flow rate required - I will do both things asap and add the details.

Do people agree with Agile that there is little difference in efficiency between combi and stored water?

Agile, when you mentioned stored water are you talking about any of vented mains, unvented mains and boiler-plus-cylinder, or did you have one in mind?

Thanks!

 

[Doctor Drivel]

Thanks all for suggestions so far - perhaps by saying "drench" shower I am being untechnical - I was thinking of one of the large round-headed showers, but have not chosen the model or checked the flow rate required - I will do both things asap and add the details.

Do people agree with Agile that there is little difference in efficiency between combi and stored water?

Modern combis are more efficient. Also your lifestyle to. IF you are one or two people with unset hours then a combis is cheaper as you are not heating water when you will not be there.

Agile, when you mentioned stored water are you talking about any of vented mains, unvented mains and boiler-plus-cylinder, or did you have one in mind?

Thanks!

Best find out what your mains can give you before any more recommendations.

 

[Doctor Drivel]

One I saw on the net wanted 12 li/min at 55 C which is more than all but the largest boilers will give.

Most average combis sold these days can give that.

there can be another problem because they are not designed to give DHW at such a high temperature.

They are look at the DHW dial.

Those kinds of showers are expected to be supplied from stored water.

Nope. From any DHW source as long as it has the flow.

There is little difference in efficiency between a combi and stored water in a normal house.

Combis use less gas, and in certain lifestyles even more.

 

[Nixt]

The 'average' combi sold today according to most sales data I've seen is the 28-30kW types, which in order to manage 55c @ 12l/min would need a rise of 40-50c @ 12l/min (depending on season). Only the higher flow ranges can reach this.

 

[Amateur99]

OK, thanks to all of you for your advice - I'll check the flow rate when I get back in there, and will check the shower's flow requirements too. Till then.

 

[gas4you]

The water flow and pressure requirements of a larger combi and that of an un-vented cylinder will be about the same to work efficiently.

One point to bear in mind is that if you go the 2 combis route, you will almost definitely need to have your gas meter upgraded to a U16 small commercial meter and any pipe work off increased in size to cope with the 2 combi's gas demand if both on together.

A point Dr Drivel is unqualified to think about as he is not in the trade and not registered for anything other than posting a load of drivel that he has googled the answers for, on here.

 

[Amateur99]

Thanks, Dave - that's helpful.

From reading other posts, if I'm going to consider either vented or unvented mains supply, I also need to make sure that the bore of the cold water pipe from the street to my boiler is at least 20mm all the way - is that correct? Or can I rely on the pressure and flow rate being adequate?

Can I measure the flow rate at the bathroom tap? Boiler is on 1st floor in kitchen, bathrooms are on 2nd floor.

Also, the flat is on the 1st and 2nd floors only, and there's no common entrance - I expect that the stopcock from the mains may not be in my property, so I might not be able to check if it's a full-bore version. Even if it is accessible, can I change it if it serves all 3 flats? Or could that adversely affect the other flats?

 

[gas4you]

Slightly wrong, the minimum supply from the street has to be 25mm, and if possible 32mm.

See BoxBashers post on another thread, he is the water regs expert