New system advice

[CHIEF]

I am new to this forum . I am in the process of having an extension done so am going to replace my 25 year old Baxi FS801rs.It is a very old property with 4 bedrooms and has single glazed sash windows(the property is listed). It has one bathroom/shower and a sink in another bedroom.We will possibly fit an en suite to the new bedroom.
I have a 25m/2 conservatory with wet underfloor heating. At present this is off the same circuit as my radiators due to constraints with pipe routing. It works ok.
My thoughts are
1. Leave it as it is and fit a combi to run everything. Broag Rehema avanta 39c or a Valliant.
2. Fit boiler as above and zone UFH and rest seperate.
3. Fit a smaller combi to run the house heating and hot water and a 5kw air source heat pump just to run the underfloor heating (no dhw) .
4. Fit Valliant boiler and Unistore cylinder to run everything.Drawback to this is cost of stored hot water.
5. Fit a big air source heat pump (Dalkin altherma) to do it all and hope to get a grant towards it.
There is me, wife and three young children in the household.
Advice and recommendations would be gratefully received.

 

[david williams]

if you are going to add a bathroom dont bother with a combi .if you want to be green go for the bigger heat pump.

 

[radswilldo]

You really need a plumber to attend and tell you what is suitable, you do not want to make an expensive mistake.