Do Combi Boilers Condense in DHW Mode?

[BriscsWK]

My understanding is that a temperature differential is required for boilers to condense and therefore work at full efficiency but I think I have read (somewhere that I can no longer find – hence the question!) that combi boilers can condense in DHW mode – is that right and if so does it apply to all combi boilers?

If combi boilers do not condense what is their efficiency and does it mean that a system boiler (assuming it is condensing in DHW mode) and say an unvented tank is therefore more efficient even with the small heat loss from the stored water?

Tks

 

[gas4you]

I may be wrong, but the only manufacturer I can remember actually stating their combi's, or some of them, condense in HW mode was/is Worcester.

 

[Deleted member 105431]

it depends on the flow temp, cold mains temp and flow rates tbh. Vaillants do condense in dhw mode dependant on the previously mentioned variables.

 

[Agile]

All condensing combis can well condense in DHW mode with the right settings.

All condensing boilers are more efficient than non condensing boilers. I really dont understand why some people dont understand this.

If a heat only boiler is heating a cylinder and has been mistakenly set for a high flow temperature to get quicker reheat then it will hardly be condensing but its still MORE efficient than a non condensing boiler.

Tony

 

[simond]

An ACV Heatmaster condenses throughout HW mode - but it is a large beastie.

 

[David937]

I may be wrong, but the only manufacturer I can remember actually stating their combi's, or some of them, condense in HW mode was/is Worcester.

My Vaillant ecoTEC+ 937 certainly condenses, when in hot water mode the maximum flow temp I've ever seen it use was 57 degrees which was when the weather was freezing. In normal weather it uses 55 degrees. Bear in mind that this boiler has a hot water store.

 

[BriscsWK]

Tks to all of you for your responses - the world of central heating is a complex thing!

Tony I Take your point about boiler efficiency – so modern boilers maybe a tad more efficient than our 25yr old Ideal Mexico Super........

Simon I saw that the ACV Heatmaster condenses throughout hot water mode but my concern with ACV/Atmos (Daalderop or Intergas)/Atag etc. and other low-country products is finding someone with knowledge of them and then the prospective spares/back-up/service etc. living on the Wirral Peninsula, which sort of pushes me to WB & Vaillant.

I was however intrigued by the ACV tank in tank technology – has anyone experience of this with either their cylinders or storage boilers?

Tks again

Stuart

 

[Agile]

Many people only think that a boiler condenses when the sales spec says it does!

Thats nonsence! All combis will condense on DHW when the conditions are right!

The difference between full condensing and not condensing on a condensing boiler is only 12% !

Tony

 

[BriscsWK]

Tony,

Do you know what efficiency our 25yr old Ideal Mexico Super RS would roughly be?

Tks again

Stuart

 

[Agile]

Perhaps about 55-65% !

Tony

 

[BigBurner]

Tony,

Do you know what efficiency our 25yr old Ideal Mexico Super RS would roughly be?

Tks again

Stuart

You can drop your gas bill by 33 to 40% by fitting a top rated boiler with integral weather compensation. Look at Broag 39C. They have dealers/service around Liverpool. They fitted many at Liverpool uni.

 

[BigBurner]

Tks to all of you for your responses - the world of central heating is a complex thing!

Tony I Take your point about boiler efficiency – so modern boilers maybe a tad more efficient than our 25yr old Ideal Mexico Super........

Simon I saw that the ACV Heatmaster condenses throughout hot water mode but my concern with ACV/Atmos (Daalderop or Intergas)/Atag etc. and other low-country products is finding someone with knowledge of them and then the prospective spares/back-up/service etc. living on the Wirral Peninsula, which sort of pushes me to WB & Vaillant.

I was however intrigued by the ACV tank in tank technology – has anyone experience of this with either their cylinders or storage boilers?

Tks again

Stuart

The tank-in-tank is super quick recovery time - it can be open vented or unvented. If unvented you need G3 and an annual service charge. The Heatmaster is a class act.

Instead of tank in tank, look at a pressurised heat bank - no G3, or annual service charge. Look at this thread: //www.diynot.com/forums/viewtopic.php?t=137289

Advance Appliances do stainless steel heat banks.

 

[BriscsWK]

Tks for extra info’ BB – had a quick read of your link and a tad above my head so will most probably be keeping it ‘simple’ in my terms.

 

[simond]

We have experience of the ACV Heatmaster and their tank in tank stuff.

The Heatmaster is a simple machine (no diverter valve) but there is limited support from the manufacturer.

We are one of the very few installers in our (Surrey) area. I have some Heatmaster install photos shortly to put on my website blog.

We recently installed one on a chimney liner with an accumulator to provide the kind of water supply the HM35 excels at, over 40 litres per min of hot water is possible if you run the store at 85C.

It is really a hybrid thermal store/combi/unvented cylinder. Rather innovative but fundamentally simple.

 

[BriscsWK]

Simon – tks again for the info’ on the Heatmaster though I’m not certain (being a simple accountant!) ‘fundamentally simple’ is phrase I would use regarding your previous sentence

Is the Heatmaster a stepped increase in cost over say the new WB 440HF i.e. more like the cost of an unvented system? If I went the unvented route would a Vaillant system boiler, uniStor/auroStor and controls be preferable to a good system boiler and controls and an ACV tank in tank cylinder in your experience?

Many tks

Stuart