Heating dilemna - unvented/combi - or do nothing?

[LondonChap]

I find it strange when plumbers recommend expensive complex ways of fixing the obvious.

What has been proposed is keep an old expensive to run boiler and installing expensive unvented cylinders and accumulators.

ATAG, an RR quality boiler, do a combi that will give 23.2 litres a minute. Five years guarantee.
http://www.atagheating.co.uk/defaul...&productgroepnaam=Combi boilers&productID=268

This is a new cheap to run top quality boiler and eliminates an expensive unvented cylinder and all those accumulators. The cost cannot be any more than those cylinders and keeping the old gas guzzling boiler. The pressure and flow is fine for a combi as long as the pipes are sized and run right. Replacing an old mains tap can improve flow. Having the cold water feed to the combi 22mm improves matters as well as the above post states. Then he has mains pressure all around and a nice big space in the airing cupboard as the big cylinder is now gone. A small radiator can be fitted in the airing cupboard if heat is needed.

I would look at a big quality combi as the first option which gives a new cheap to run boiler (energy is not getting cheaper) and mains pressure hot water at high flow and pressure rates. The combi also will not run out of hot water, important with teenage girls, and gives hot water for ever. Why do people do things the hard way?

EDIT: 23.2 litres a minute gives 696 litres in 30 minutes. That is a big cylinder to hold that amount of hot water. In 15 minutes that is 348 litres of hot water delivered. A 350 litre unvented cylinder very big and very expensive.

 

[Dan Robinson]

Atag Q51C gives 23.2 litres at 38degrees (not delta). It is also a metre wide. It is also the better part of 3 grand

You won't be running it of a standard gas supply either.


Cheap trying.

 

[LondonChap]

Atag Q51C gives 23.2 litres at 38degrees (not delta). It is also a metre wide. It is also the better part of 3 grand

You won't be running it of a standard gas supply either.


Cheap trying.

I just looked. It can run off as standard gas supply with room to spare. Gas consumption: - 4.86 m3/h. A standard meter delivers 6 m3/h.
Keep trying

£3K for all in one quality, top rated, product. Price up a quality boiler a 350 litre unvented cylinder and the accumulators and see which is the cheapest.

A 350 litre unvented cylinder and the accumulators will be more expensive and then the long labour times to install on top again. Then price a 700 litre cylinder. Wow! Combis are cheap to install. Oh and he has another cupboard with the combi.
Keep trying

 

[Terry lambert]

Why not run a 22 mm cold feed up to the cylinder position, that way if your not happy with the performance with the 15 mm incoming main, you only have to upgrade the pipe out to the road.

You then wouldn't need to disturb your new flooring

 

[LondonChap]

Untitled

• Dan Robinson
• 12 May 2012
• 3

Here's three we fitted earlier .

Big bath fills very rapidly - house is 4 storeys with a pressure of 1.5 bar in the loft and a 15mm riser. Customer very happy indeed.

Nice. Accumulators are an obvious remedy in many cases but most plumbers have never heard of them. What make and size are those? What is the cold water storage? Are they being covered in an insulation blanket?

 

[Smurfin]

This whole thing seems to get more and more confusing, with options getting more and more expensive, and different opinions left right and centre.

Part of me thinks I should do nothing but stick a central heavy duty pump upstairs in the airing cupboard, but there again I hate the noise and I want something which is going to last us. Plus, I'm quite interested in going down the solar route in a year or two's time.

What's the general opinion on my boiler though? Someone mentioned running an expensive boiler and heating a bigger, more expensive tank than we have now just doesn't make sense. But when it comes to boilers, I've always thought "if it ain't broke, don't fix it". It's an Ideal Classic (75% efficient), and a couple of independant people have both told me these are really well made and reliable.

 

[LondonChap]

This whole thing seems to get more and more confusing, with options getting more and more expensive, and different opinions left right and centre.

Part of me thinks I should do nothing but stick a central heavy duty pump upstairs in the airing cupboard, but there again I hate the noise and I want something which is going to last us. Plus, I'm quite interested in going down the solar route in a year or two's time.

What's the general opinion on my boiler though? Someone mentioned running an expensive boiler and heating a bigger, more expensive tank than we have now just doesn't make sense. But when it comes to boilers, I've always thought "if it ain't broke, don't fix it". It's an Ideal Classic (75% efficient), and a couple of independant people have both told me these are really well made and reliable.

Your boiler is inefficient by modern standards. You can save 1/3 of your gas bill by getting a top efficient job. The boiler is not getting any younger and parts will fail sooner rather than later. Look at the ATAG combi I linked to to as the first line of attack. Keep it simple. KISS. You need a new boiler anyhow. Consider the points I put forward. Do you have a utility room? Garage? To put a combi in?

 

[Smurfin]

I've been quoted almost £3300 plus VAT for a WB 42 CDi combi (located in the loft). Expensive.

But why do I need to change the boiler anyway? It works.

Going back to the combi idea, I don't understand why there is a so much conflicting advice. We're a family of 4 in a 5 bed house....you sure a combi is going to be adequate?

 

[LondonChap]

I've been quoted almost £3300 plus VAT for a WB 42 CDi combi (located in the loft). Expensive.

But why do I need to change the boiler anyway? It works.

The boiler is now old and inefficient and not getting any younger. You can drop your gas bill by approximately one third by a new combi. Also combis do not have hot water standing losses that are in cylinders. The ATAG has integrated weather compensation to also drop bills and promote better comfort in the home.

Will the WB have a separate 22mm cold feed to it from the mains stop tap? £3300 is not bad, depending on work or course. The WB delivers 16 litres a minute. Not bad but not as good as the ATAG.

A large unvented cylinder (not to mention any accumulators) is not cheap and you still have the old expensive to run boiler. The unvented cylinder needs a yearly service which many never cost in. The service cost buys a lot of gas. Add in a new quality boiler and the higher flow combis then start to shine in installation cost and will perform the same as the cylinder when piped up right. Well they perform better as they can run forever and not run out of hot water.

Going back to the combi idea, I don't understand why there is a so much conflicting advice. We're a family of 4 in a 5 bed house....you sure a combi is going to be adequate?

It depends on the combi of course. The ATAG 51C delivers over 23 litres per minute, which is about the same as your mains cold water supply going by the figures you gave. The unvented cylinder cannot deliver more than the mains pipe can give it. So they are equal in hot water delivery.

The ATAG will deal with two simultaneous showers, which is probably the prime point on hot water delivery. It will fill one bath very quickly.

The ATAG in your situation will not disappoint. You will get a cheap to run boiler which makes a big difference in a big 5 bed house. It delivers all the hot water you need.

The WB 42KW will just do two showers simultaneously and fill a bath OK. No one ever complains of the bath fills from large combis.

The unvented cylinder will just deliver two showers simultaneously with 23 litres a minute at the mains pipe. Even if it is 50 litres a minute at the mains they even struggle on filling two baths simultaneously.

A point to bare in mind: These high water consuming full length body jet showers exhaust cylinders very quickly they need very large expensive cylinders. Some have gone over to using instantly heated hot water, using commercial multi-point water heaters.

Using say an ATAG your two teenage daughters can stay in the two showers all day, while cylinders run out of hot water.

 

[Smurfin]

Interesting points, I'm still confused!

Any one to counterbalance LondonChap's strong push down the combi/ATAG route?

 

[LondonChap]

Interesting points, I'm still confused!

Point out your confusion.

 

[gaswizzard]

EDIT: 23.2 litres a minute gives 696 litres in 30 minutes. That is a big cylinder to hold that amount of hot water. In 15 minutes that is 348 litres of hot water delivered. A 350 litre unvented cylinder very big and very expensive.

It seems you have based these figures on a store temp of 40c (no mixing)? ,

With a store temp of 65c and a mixed outlet temp of 40c a 300 litre tank would be depleted of hot water in around 25 minutes (excluding reheat time) , the 350 litre (odd size ) in around 29 minutes (flow rate based on 22 l/m).

The above is in response of your shower example.

 

[gaswizzard]

Interesting points, I'm still confused!

Any one to counterbalance LondonChap's strong push down the combi/ATAG route?

No doubt you are confused with some of the mis-guided advice being posted on here.

 

[Smurfin]

Ok, this is getting interesting (or not). Just had British Gas round, and this was the first guy who took proper readings, both static and dynamic. I'm a bit shocked:

2 bar mains pressure.
10 litres a minute

With 2 taps open, this drops to 7 litres a minute.

Incoming mains from road is 22mm, but 15mm from the stopcock onwards.

I asked how much difference changing from 15mm to 22mm would make, but he said you wouldn't actually know until you'd done it.

His advice was to look at 2 options:

1. Change to 22mm from the stopcock to the cylinder, change to unvented with accumulators in the loft: downside being additional cost (I have no idea how much they are), and the fact that once the accumulator is exhausted, pressure would immediately drop to being crap again. Advantages would be good pressure throughout the house.

2. Stay with the vented system, and just stick a whole house pump in the airing cupboard. Change the vented cylinder to a new 250 litre one if and when I decide I really need a bigger tank (and possibly move to solar).

Thoughts? Option 2 looks like the most obvious and sensible choice right now.

 

[Dan Robinson]

As an Atag installer I just would never specify a combi in this sort of property unless the customer expressly wanted one and understood the limitations.

They can and do go wrong. When they do - no backup.

If you have the space, maintain a tanked system.

Accumulators vary in cost depending on size. the ones in my picture are storing cold water for dual use.

As GW has said, LC has not used the correct figures, although on the face of it the 51C would cope. But seriously a boiler 1 metre wide - in a house!!!??? Yes it will fit on a standard gas meter, but not a standard gas pipe unless the boiler was only a few metres away form the gas metre then you are up to a fairly chunky and expensive gas supply pretty quickly with other appliances as well.

It is also only modulating down to 9kW. totally overkill, and Atag will agree. It was designed for large properties with low hot water needs like churches, schools, and offices.


By all means use an Atag, but one of the smaller ones in conjunction with a cylinder. yes I would suggest changing the boiler as part of the works. How you handle the water situation is a tricky one. You don't want pumps, but the alternation will be expensive. the Worcester quote you have is very cheap, but from your descriptions here - it is the wrong specification for you - in the long to medium term at least.

Having a pump on the existing setup is of course relatively cheap as chips.

Your current mains supply is not going to cut it though with any system directly fed off the mains. So a pump or accumulated option is the best way forward unless you fancy replacing your mains water pipe. Going from 15mm to 22mm will improve things, but I doubt it will to the extent that the cost is worth while. Divert the funds to another part of the overall project.