30 KW of electric heat is over 100K BTU of heating. Do you really need this much (or do you just like to be able to heat the house quickly)? Have you made any attempt to calculate how much heat your house needs (e.g. ACCA Manual J calculation)? Unless your electric is crazy cheap, this is going to be expensive to run.
What do you have for heat now on the first floor? How many BTUs does it produce?
Finally, what type of electric heat are you installing? Baseboard? Central furnace? You have a coupe of outs depending on interpretation:
220.51 allows you to calculate less than 100% of that 15KW load if it runs on a duty cycle or intermittently. A thermostat will cause the furnace to run intermittently.
220.82(C)(4) and (5) allows electric heat to be calculated at 65% for 1 to 3 heating units or 40% if four or more. If each electric furnace is two stage, you may be able to argue that this is 4 separate units. Same with 4 or more baseboard heaters.
A heat pump throws a wrench into this, as you have to add the compressor value at 100%. Also 220.82(C)(6) could be used against you if you had a small heating system where it would be expected to run at full load most of the time.
The above rules are for new installs. 220.83(B) has the rules for upgrades, and it requires all space heating to be added at 100% and then add the other existing items as it indicates (40%).
So there are no cut and dried answers to your question without knowing more specifics or what subsection of 220.82(C) the inspector is going to let you use or are you using 22.83. I'd also be hesitant to set back your thermostats much if you're going to use the 40% or 65% sizing reductions. Kicking in a full 30 KW of heat in a marginal service could be asking for trouble.