Hi Keith,
No one deliberately uses road diesel for household or industrial heating, normal heating fuel is either kerosene (Esso Blue paraffin of old) or gas oil #1 for household use, or gas oil #3 for heavy industrial use.
There are two peak consumption periods for crude oil - obviously one is the American and European winter, and the other during the summer (vacation driving in the USA and Europe, air-conditioning in the USA, and winter fuel use in the Southern hemisphere).
Part of the problem is that you can't take a barrel of crude oil and just make diesel. The refinery will typically (and very approximately) refine a barrel of oil into:
10% LPG - very much depends on the nature of the crude oil
25% naphtha (petrol)
13% kerosene
13% diesel
10% heavy gas oil
20% lubricating oil
10% residue (road tar)
Today the refinery can crack excess heavy gas oil and lube oil fractions into additional naphtha - and boost petrol production from 25% to nearly 50%
But today the same can't be done for diesel - the first GTL refinery in Qatar which will make extra, high quality diesel, from other parts of crude oil is still being commissioned.
So diesel production is limited to how much crude oil is processed, and if a refinery is already running at 100% capacity - then you could import from somewhere else (at a higher price - shipping) or let price reduce demand.
Robert