If they did a Manual J, they'll know how much heat strip backup is needed. Perhaps they'd be willing to provide proof of the load calc. A company that does a load calc is a company that cares about the work they do (for the most part), so I'd give them a close look. Were you comfortable with this company? What model numbers for equipment did they provide you? Electric service available at the air handler also plays a role in how much heating kW you can have; hopefully the contractors kept this in mind.

Thanks for replying, Ryan Hughes. I'll be calling the two firms that claimed to have done a Manual J calculation shortly and asking those questions. The third one wants $150 to use Manual J, cancelled if I accept their proposal.

Electric service did come up with one company. He stated that our existing service (100 amp, split 60/40 at the outside box) is inadequate, and proposed combining those two for the heat pump and adding an additional 60 amp just for the electric heat.

Another question has come up. I have two 16 x 16" return openings. One firm wants to upgrade one of them to 16 X 30", giving a total of 736 sq. inches. Another proposes to convert both to 16 X 20, for a total of 640 sq. inches. The third didn't mention it, and I'll question them as well. Carrier says the returns should be 200 sq. inches per ton of cooling.
Carl

Can you post model numbers of the equipment you've been quoted? It will have sizing information (tons) as well as what kind of equipment they're proposing. Having sufficient return air is important and helps improve comfort, so I give credit to the companies addressing these issues as well as running load calcs. Load calcs should involve measurements and recording data--did you notice any contractors doing this? They might run the calculation at their office with a program.

I have a 30 amp breaker for my 3 ton heat pump, and a 60 amp breaker for my 15 kw aux electric strip heat.

Take care.

Got a third proposal froma firm that handles both Carrier and Lennox. The rep did the load calc on his laptop in our living room. He also spent time (that the others didn't) talking about insulation, and the rebates and services offered by our local utility company. He's e-mailing me the proposals, as well as a copy of the load calc. When I get them, I'll post the quotations received so far.
Thanks for your responses.
Carl