Originally posted by paulockenden
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To answer this question we need to consider average heating loads across the UK. Many dwellings in our country are old buildings with relatively poor insulation, and this means an output of around 8–10kW is typically required to keep a house warm in winter.
Looking at my loop usage in the late evening at this time of year it seems to be averaging about 5kW - this is to maintain the existing living room temperature and heat and then maintain the bedroom - which is in a not particularly well insulated loft bedroom. Our boiler is a 23kW unit so that would be a modulation ratio of 4.6 - just barely within 5:1, but that is with two rooms heating.
Now consider night time - the bedroom radiator is the only one scheduled to be on, this is averaging approximately 2kW, although it does vary quite a bit from day to day - this would be well outside the modulation ratio of a 5:1 boiler so would result in the boiler cycling on and off all through the night.
Their article also doesn't take into account spring and autumn weather where heat demands are considerably less, and higher modulation ratios become even more useful.
So I think its fair to say that if you have a well insulated house (we don't!) or make use of zoning to have only one or two zones active at some times of the day (especially a bedroom radiator at night) then a higher modulation ratio is definitely useful, especially in moderate weather!
Firstly, with a high ratio, the flame in the boiler is very small, and therefore weak. If it’s disturbed (e.g. by additional air movement), the flame might become unstable and unreliable, or even go out. Resulting in poor flame detection and/or nuisance tripping, the boiler will need to restart, which is what modulation is designed to avoid.
Secondly, higher modulation ratios don’t necessarily mean lower energy usage. The primary efficiency consideration of the boiler is the return water temperature – the lower the better. The gains made in energy efficiency by moving a modulation ratio from 5:1 to 10: 1 with the same return water temperature are negligible.
Given that this article is promoted by Baxi and the other one by Vokera, I think this can be regarded as an opinion piece on Baxi's part.
The first article is the one I would place faith in.
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