
The biggest outstanding question in my head, and probably always has been since we decided on the structure type, is the heating. I'm convinced on the comfort of Underfloor, and happy with the idea of MHRV. The problems start once we get into sourcing the energy.
Currently, you can probably supply fit & commission a condensing oil burner & tank for about €3,000. This then has a high constant outlay over the lifetime of the burner, but low capital cost.
The other option is a heat-pump. However - the area to be heated in our house is significant, and so a single pump (on the premise of single-phase electricity supply) would not cut it - certainly for a traditional build. So - I can either install 2 pumps (say 14kW + 11kW), install Oil and a single pump 16kW, or and what I had been thinking, is to chance a single 16kW with an immersion coil and bet on the insulation finish on the house to be enough to reduce the load.
I've been in an ICF house that was about 20% smaller than mine in area, but heated with a single 11kW A2W pump the inhabitants were very happy, but ran it at 18C and the property had a much smaller glazing area. Thats what pushed me to a single 16kW pump and hoping for the best.
A potential supplier modeled the heating requirement (subject to massive assumptions and average weather) and it looks like once we go below 0C we need backup from the immersion coil.
On top of all of this is solar. 'Free' energy for nearly 3 seasons sounds like a great buy, but with the Heat Pumps able to operate at night & heat a buffer during these times it's saving the night-rate electricity - currently about 8c/h.
The only thing thats not making me pull away from all and any renewables is that we will be living there long enough for the bigger ROI plays to pay out. Anything around a 20 yr horizon isn't too daunting.. more than that and I have to think hard. You can guess where I think our ROI will be!