UFH or Infrared Heating

[TerryE]

I have a passive-class house and I use resistive heating, that is I have a wet UFH system in-slab.  OK our ground-floor footprint is a lot less than yours at less than 80m² living space footprint per floor, but we do have 3 floors.  Our slab and frame supplier charge us less than £2½K to add the heating loops into the slab pour.  I did the rest for maybe £500 or so, so our CH worked out at around £3K total.  One of the reasons that it was that cheap is that I use a resistive heater (a "Willis") to heat my UFH circulating water.  We only heat our ground-floor with UFH, but I do use an oil-filler on the 1st and 2nd floor to top up overnight in the coldest months (up to ~10 kWh) at a total price less than £200 including the smart switches controlled by my home automation system. 

 

However, I also did the groundwork to add an ASHP at a later stage (pre laid insulated pipework to ASHP location, plur power spur) if and when the number made sense to do so.  I figured that we'd go resistive until we had enough data to make an informed decision., and we've never reached a threshold where we have enough of a payback to make the investment case viable.  During Dec/Jan about 70% of our electricity use is off-peak and for space on DHW heating this is 100% efficiency — that is 30 kWh of electricity generates 30 kWh heat.  With an ASHP at the ~30°C circulation temperatures with long cycle times we would be looking at CoP of nearer 4 so we would need 7½ kWh electricity to achieve the same.  That's a 22½ kWh energy saving.  Based on our current year-round actuals, it makes sense for us to defer this decision, but we still have the option to add an ASHP should it make sense to do so.  

• It seems to me that this IR panel route locks you into a CoP of 1.0 at a high installation cost.
• If you build to passive class (or near, e.g. wall, slab and roof U-value 0.15 W/m²K, decent triple glazing, MVHR, airtightness 0.6 ACH, or better), then the whole dynamic and sweet spot for heating changes.  For example you really only need ground-floor heating
• Our in-slab heating cost us maybe £30/m² based on the ground floor, but that was for the total CH system costs, and we got 3 floors heated for this price.

Edited February 24, 2023 by TerryE