Thanks for all the replies. My friend says starting his 1720D with and without the thermostart is night and day in very cold temperatures.
thanks
Duane
I guess it depends on what you call very cold conditions. My YM1301D starts without it down to about 35 deg F. It starts pretty easily down to about 25 deg F using the thermostart. I haven't tried starting it at temps below 25 yet.