SuperV8

Thanks, i'll have a read.

I installed lovely new composite front and rear doors 2 years ago - so won't be changing these anytime soon. I did 'briefly' think about digging up our floors - but this is simply not feasible whilst living in the house with my young family. I am up for a challenge but this would be a step too far!

I think I was confusing DT! and deg! from here: https://www.clyderadiators.co.uk/delta-t-conversion so using the 35deg recommendation - the conversion factor should be 0.63! Which makes my heatloss: 900watts = 1430 1140watts = 1810 So I need to look for 1430 and 1810ish DT50 rads - which seems much more reasonable.

Thank you for the detailed reply. Right - i'll scrap the UFH idea and concentrate on rads. Looking at rads, they seem to be listed in watts at DT50 - I've found a conversion factor to divide by 0.21 to get to DT15 output. I have 900 and 1140watts heatloss in my kitchen and living room respectively - which would mean rads rated at DT50 of around 4300w and 5500w which seem huge! Unless i'm missing something - (highly likely!) is the radiator DT different to system DT?

Hi, Have been reading many topic's regarding UFH and to basically not to bother unless you don't have a very well insulated slab. My project: 1980 small detached house - concrete slab floor, filled cavity walls, recent double glazing, 300mm loft insulation. I have done a heat loss survey using heat engineer - which comes in around 4200w heat loss on a -3.5degC day. lower than I was thinking, mainly helped I think as it's not a large house at 76m2 total floor area. I am fitting a new kitchen and removing a stud wall so now (if ever) would be a good time to fit an overlay UFH system - the type you can tile directly onto. They are 20mm think panels - I only have about space for 45mm total floor increase available due to front door opening in. Can't go to the length of digging up floors (doing this around my small family) Current system is gas system boiler/rads and hotwater heat store. Looking at going to a heatpump in the near future. I have gone through the UFH loss excel sheet shared elsewhere on here which looks like this: using 20mm XPS/aluminium UFH panels at 0.035W/m.k My heat loss survey said my downstairs rooms would required 2200w on -3.5deg day. So not great - loosing 900w into the floor! Is this 900w per hour so I can calculate by the ASHP COP and kW/h electricity cost to work out cost per hour? But with only 27 deg floor temp and delta T of 5 that gives a flow temp of 28.5? so a heatpump should be very efficient at that low temp. I am ultimately bound by running costs. I know fitting large rads would loose less heat into the floor - but how do I calculate the actual running costs UFH vs rads? Even though I loose more heat through the floor - if this heat is provided more efficiently it could still work out cheaper? Any thoughts/help greatly appreciated. Thanks, Tom.