I am trying to update my "as built" SAP ready for sign off but have hit a problem with regards to the use of Sunamp heat storage for hot water. Has anyone looked at how these can be described to SAP (I'm using stroma2009). The only choices seem to be "Electrical instantaneous point of use" or "electrical immersion". The former doesn't really apply and the latter assumes a water storage cylinder.  If I use real numbers for the water storage volume (<15lt) and daily losses (0.6kw) I get a