modulation range

damaan1967 · 30 Oct 2016 at 17:35

Sorry I keep reading about modulation range for combi boilers: what is it? What is a good one?

GeForce · 30 Oct 2016 at 18:05

It is the ratio of the boiler minimum output to its maximum.

For example a 24kW boiler with a 1:4 range can reduce its output to 6kW. So if you're just running a single hot tap (say for washing up) the boiler can produce a decent flow of the right temperature water (unlike older non-modulating combis which will burn your fingers off for a bit and then go cold for a while).

In general higher is better; I think 1:5 or 1:6 is considered "good", but really what's best for you is highly dependent on your circumstances.

damaan1967 · 30 Oct 2016 at 18:09

So a Viessman with a range 1:20 is good or bad?

GeForce · 30 Oct 2016 at 18:10

1:20 is very good.

I can't give any advice re. Veissman vs other makes though. Perhaps someone else can.

a1ex2001 · 30 Oct 2016 at 21:25

1:20 is excellent and viessman get good reviews.

robj20 · 31 Oct 2016 at 08:25

Modulation is mostly for central heating, allows a lower temperature when required to help keep the boiler in its condensing mode, but also allows you to ramp it up when required.

a1ex2001 · 31 Oct 2016 at 15:05

robj20 said:
Modulation is mostly for central heating, allows a lower temperature when required to help keep the boiler in its condensing mode, but also allows you to ramp it up when required.

That was my understanding too! Anything that maximises the time a boiler is running at it's most efficient is a big bonus the current/next gen gas valves are a massive improvement I'm also looking forward to seeing more boilers using the exhaust gas to preheat the water entering the heat exchanger which is another great feature.

Lumeycom · 31 Oct 2016 at 17:28

modulation is also useful/required if you have solar hot water and your boiler feed is via a heat store.