Would you say try and specc each room by around 10% to 20% uplift and if not possible make it up in other areas? With us, the whole house stays open, all the doors etc, except for the bedrooms at night which remain slightly ajar. I was thinking bedrooms no more than 15% maximum.
Thats definitely not a bad approach, combined with a bit of pragmatism. If there is a nice radiator already present which is a few tens of watts short, dont worry or make it up from adjacent rooms.
Its also worth looking at absolute figures. 20% sounds like a lot, but if its 20% of 400W = 80W it really isnt. Bear in mind the heat loss calculations are subject to errors of 100% or more.
If they cause a problem with rads I wouldn't worry too much about bathrooms or toilets either. My bathroom has a towel rail which emits almost nothing at 40C. All the calcs said to replace or supplement it but I didn't, hoping that the combination of steam from running a bath/shower and heat from the adjacent landing would do the job, which it has. Likewise I have an unheated downstairs toilet which remains unheated other than by transfer from the adjacent hallway.
There is quite a substantial price difference between keeping existing radiators and replacing them, around £2500 more for the panels.
Thats a lot, but of course some will absolutely be necessary. Another approach is two stage, do the high deficit and easy ones first then plan another tranche once you know if the lower deficit difficult ones are really a problem. The only 'effort' lost is a drain down and some inhibitor, not insignificant but not crippling if it avoids replacing several rads.
It is a bit of a balancing act and I must confess I spent an inordinate amount of time on it, bedrooms were fairly easy but the living rooms much more difficult to juggle. I could have spent three times as much if I bothered to look at individual manufacturer specs, but as I say above I just used the stelrad figures assuming all panel rads are the same to within the margin of error on everything else. For any given type and height they give you wattage per metre length which is a further simplification that a simple spreadsheet can assist with.
This post was modified 3 hours ago 3 times by JamesPa
4kW peak of solar PV since 2011; EV and a 1930s house which has been partially renovated to improve its efficiency. 7kW Vaillant heat pump.
This is my current workout with keeping as many existing designer radiators as possible, and only slapping in a 2m K3 in the living room:
The spreadsheet shows positive figures as the shortfall, in red, and the negative figures are green and good as these are higher than the existing heat loss. Hope it makes sense.
This looks OK. Overall you have roughly the right amount of heat going into each floor.
What is the design temps for the bedrooms? Is it already low at 18C, or have they designed to 21C so less of an issue with the bedrooms being a bit on the low side? Also, heat rises, so I wouldn't be too concerned if bedrooms on higher floors are a little under specced (unless you like toasty bedrooms)
The main living space on the ground floor maybe more of a concern (to me). I would focus on that, getting as much heat into those rooms as possible, as if the ground floor main living space is cold, it's all down hill from there and risk ending up with a living space that is hard to heat and bedrooms that are roasting by the time you go to bed (the opposite of what I prefer) as the heat constantly escapes to the higher floors.
Samsung 12kW gen6 ASHP with 50L volumiser and all new large radiators. 7.2kWp solar (south facing), Tesla PW3 (13.5kW)
Solar generation completely offsets ASHP usage annually. We no longer burn ~1600L of kerosene annually.
