As I said in the introduction thread my partner and I are planning to extend our Victorian semi.  We are wondering whether it would also be a good time to replace our 14-year-old combi boiler with a heat pump system.  We have planning permission but yet to complete detail drawings or engage builders, so we hope the right time to be thinking about making sure the building could work with low temperature heating.  I hope this post hasn't got too long but there is so much to get straight.  Any advice or guidance is welcome!

The house is currently about 120 square metres with the extension planned to take us up to around 160.  Typical  layout with a wing extending out the back of the main house.  The original house had solid walls.  The kitchen wing has been previously extended, in the early 90s so the kitchen and the bathroom above have a mix of solid walls and insulated cavity.  The extension will fill in the internal corner between the original house and the kitchen and add a two storey extension on the gable end, so will cover some of the solid walls, but some will remain and several chimneys, so I think the heat load will be quite high.  I need to make the plunge and get some installers in to do calculations on this: hopefully working from plans will not be an obstacle.

Looking at the particular features of the house and our plans leaves me with a number of questions.

I am wondering what to do with the suspended wooden floors downstairs and whether underfloor heating is a sensible choice for these rooms.

The back room, which will end up being part of the open plan kitchen-diner and having no external walls has a suspended floor over a shallow void.  The boards are, I think, original and we would like to retain.  Could I lift the boards, insulate, fit UFH and re-fit?  What other options would I have?

The front room and hall are over a cellar.  Front room currently insulated with kingspan boards, the hallway just has a lath and plaster ceiling in the cellar.  I've seen some UFH spreader plate systems that are said to be suitable for fitting from below.  Might they be suitable for these two rooms?  Is there anybody on the forums that has experience with these sorts of systems, good or bad?

The kitchen has a direct-to-earth floor.  We will be extending this room significantly, so I think we want to go for a screeded under floor system over insulation here.  Anything in particular to be aware of with the existing areas?  I guess we would ask our builders to excavate out to get the depth for insulation and the screed with the UFH pipes.

For new rooms upstairs, what are the relative merits of underfloor heating against fitting radiators?

In terms of plumbing layout, I am thinking that the plant room could be in our new utility room with the heat pump itself standing out the back of this.  It would be below a window: does that lead to any particular considerations?  We will be too close to the neighbours to put the heat pump at the side of the house.  We have quite a large bathroom so I think I would site the hot water cylinder in there.  That would be upstairs from the plant room but with reasonably straightforward pipe runs.  Cylinders for heat pump systems look huge: are structural calculations required for the joists that will be supporting the cylinder?

Matthew