There is a village of Scaldwell just a short distance north of Northampton (in the former Honour of Huntingdon). There seems to be a small family of Scaldwell's that obviously have taken their name from this village.
It apparrently is from the Old English with a Scandinvian prefix to give "Shallow spring or stream".
This seems to run with the OE origin of Caldwell but doesn't necessarily solve our Scots name problems.
The Scaldwell coat of arms has been included in the carved arms of the Angell family ontheir Stockwell Park property (from Elizabeth Scaldwell of Brixton).
They are described as - "Azure a Cross Pattee Fitchy between 8 Estoiles in Orle Or"
This is the IDENTICAL coat of arms of the English Caldwell family of that region which would indicate that Scaldwell and Caldwell were interchangeable.