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I'd have thought 30kw is too big. if you add up the watt output of each of your radiators and UFH system that gives you a good idea of the heating output.
That being said, check out the 'modulation range'. thats basically how low the boiler can go without going into 'anti-cycling' mode - lower is better and it's more efficient to avoid cycling (in theory). Viessman seem to be the best boiler manufacturer in this rgeard.
in our recent renovation, we put in a vaillant ecotec 35. we have about 12-15kw radiators/ufh and the boiler can modulate down to 3kw ish. because it's on weather compensation it basically just ticks over at this power output giving a temp of around 40-50c in the radiators and uses around 80kw of gas per day on a minus temp day (which is still a lot of gas at current prices).
we went for an overly complicated system with different zone controls for the ufh - but in theory, you can just run the ufh of the main radiator circuit i think with a manual temperature valve used to reduce the temps. if you're running weather compensation, this shouldn't be an issue as the boiler is basically always on.
caveats- i am not heating expert (heatgeek is a great website) and i regret some of the choices we made with our system and the vaillant boiler has broken down about 6 times.
In hindsight, i wish we went with an ASHP and internally insulated when we were renovating.
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terlg
Hi all,
I am potentially needing to replace my boiler as it has just broken. I was intending on replacing in 12 months when we were planning on extending the ground floor but unfortunately not the way it has panned out.
I currently have a Combi boiler and will replace with a Combi as well. As part of the ground floor extension I will be adding underfloor heating (a wet system). Are there any considerations for me buying the boiler today? Or can UFH just be retrofitted when ground floor is done and radiators in ground floor are removed. We will still have 6 radiators upstairs.
Also from a size perspective is 30kw right for UFH, 6 radiators and 2 bathrooms (1 bath shower combo, 1 shower).
Many thanks,
Tom