Sunflower germination

so i got some sunflower seeds, evening sun for a plan to do a row of about 6-8 along a fence that has the sun set on at front of house. should look nice if works for public passing by

i have placed in a seed tray and covered with sandy soil

i have the tray on a windowsill in my spare room that sits above a radiator.  (almost above where there final position will be)

but are these conditions ideal for germination

spring sun setting on them but also the warmness of radiator means i need to keep an eye on to ensure dont dry out.  

any further tips?

ty