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Last time I mention it I entered the GC thread 😂. Just under 200sqm, but this is rural-ish Scotland outside Glasgow, so GC prices need not apply.
The heat loss calcs are over cooked IMO. And, they were based on several factors that are now less of an issue such as increased insulation, soon to be replaced windows, a blocked up shitty/drafty door and so on. But they would only calc on the existing fabric so it was impossible to get any movement here.
We had 6 installers quote and all calcs were around the same…
We’re only 10 days away from install so I doubt there is much I can change but I’ll see what they say about zoning. I’d be fine with one zone but they were not confident it could be done purely with the ASHP specced without a split gas system.
andos-
It's fine to have zoning hardware installed and not use it; just set the 'upstairs' thermostat to 30degC so it will never shut that circuit off, and the whole house then becomes a single zone. It's just obvs better to not end up paying for a load of redundant thermostats, valves, actuators & shit, but there's no harm in having all that stuff installed but unused.
I've just physically ripped out a load gubbins from my system, went from 3x zones to 1x, but I always configured it all as a 'single' zone from the beginning, as above.
The buffer tank is a big one though; if one has been specced, do what you can to avoid having it installed imo.
ectoplasmosis
How big is your house?
I'd bet big that your heat loss calc is overcooked, everybody's is. Ours came to an alleged 9.5kW total loss at -2degC, but the actual measured loss is ~6kW at -2degC. I had to fight to get the originally-specced 10kW Vaillant bumped down to a 7kW.
Zoning doesn't really work in practice, the warm rooms will always be losing heat to the unheated cold rooms causing flow temperatures to increase and the heat pump to work harder. It's also always more efficient to have as much water volume circulating as possible; shutting off radiators and reducing volume causes more on/off cycling which kills efficiency. Much more efficient and comfortable to balance the whole system properly and constantly heat the entire house as a single zone.