Combination v. Condensing

[Henryv]

I have an old boiler and a single pipe system so have decided
to replace it!
Which is the best type of boiler - Combination or condensing,
ignoring the running cost or efficiency differences.
Which is the best, most reliable, quietest?
There is just the two of us and we live in a 3 bedroom bungalow. The boiler will be in a room at the back of the garage.


Henry.

 

[Paul Barker]

they r all condensing.

regular condensing boiler with dhw cylinder and rip out old pipework, repipe with two pipes and probably new rads. TRVs lagging pipes in garage.

Massive job.. start saving.

 

[Henryv]

Thanks Paul,
I thought the combi did not need a tank?
I thought it just heated the water from the mains as it was being drawn?

Henry.

 

[Gasguru]

Henry there are generally 4 types of boiler in use (although there are other configurations)

Heat only boiler - this is the traditional boiler that requires pumps, zone valves and a hot water cylinder (either low or high pressure) added to provide heating and hot water.

System boiler - this normally just requires zone valves and a cylinder (either low or high pressure) to be added. (But many variants of this type of boiler are available)

Combination boilers - provides mains pressure hot water and heating. (No cylinder required)

Storage combination boiler - provides mains pressure hot water at a higher initial flowrate and heating. (The boiler itself contains a very small "cylinder")



Condensing just refers to the manor in which a little extra heat energy is extracted from the gas. All boilers above are available as a condensing boiler. Nearly all installations will require the boiler to be of a condensing type.


Your old system probably has a heat only boiler combined with a cylinder.
This system can give a higher flow rate than a combi and has the advantage of an immersion heater in the cylinder to provide backup hot water. Paul is suggesting you keep a similar setup and convert the radiator pipework to a modern 2 pipe setup.

 

[Henryv]

Many thanks Gasguru,
What advantages does the "System boiler" have over the
"Storage Combination Boiler" as this would seem a lot simpler to install?

Henry.

 

[Gasguru]

What advantages does the "System boiler" have over the "Storage Combination Boiler" as this would seem a lot simpler to install?

Henry.

A system boiler is just a heat only boiler with a pump (sometimes also the zone valves) and is designed to work with an external cylinder. This setup will cost more than a storage combi in both materials and labour. Its more complicated than a storage combi setup.

Look at the manufacturers sites they often have diagrams of each system.

There is a lot more to heating systems than has been mentioned so far - existing water supply pressure/flowrates, existing pipework condition, existing taps and fitting also come into the equation.

 

[baxpoti]

A system boiler is just a heat only boiler with a pump (sometimes also the zone valves) .

Can also have an expansion vessel, PRV and manual or AAV, thermistors for DHW to prevent scalding etc.

 

[Gasguru]

I was trying to keep it simple otherwise this could go on forever

 

[Henryv]

Thank you for all your advice.
Most appreciated.

Henry.

 

[Bambergaspipe]

Thank you for all your advice.
Most appreciated.

Henry.

If you fit a combi, don`t expect to open 2 taps at once (hot water) or fill a bath in less than 45 mins.

 

[Henryv]

Thanks Bamber 'G'
I am not going for the combi.
I think it will be a Vaillant system boiler.

Henry.

Thank you for all your advice.
Most appreciated.

Henry.

If you fit a combi, don`t expect to open 2 taps at once (hot water) or fill a bath in less than 45 mins.

 

[Doctor Drivel]

Thank you for all your advice.
Most appreciated.

Henry.

If you fit a combi, don`t expect to open 2 taps at once (hot water) or fill a bath in less than 45 mins.

Which combis are you on about? There are fast flowrate combis around - many of them.

 

[Doctor Drivel]

Thanks Bamber 'G'
I am not going for the combi.
I think it will be a Vaillant system boiler.

Fit a high flowrate combi. High pressure showers.

 

[Henryv]

Which do you recommend?
Why would a 'high flow rate combi' be better than a 'system
condensing boiler' (apart from the power shower)?
How reliable are they?

Henry.

Thanks Bamber 'G'
I am not going for the combi.
I think it will be a Vaillant system boiler.

Fit a high flowrate combi. High pressure showers.

 

[Dan Robinson]

It depends on how much hot water you use. I would suggest a high flow combi would be adequate, but run a search of the forums - this is one of the most heavily debated topics.