I will be adding a subpanel next to the main panel. The subpanel is rated at 100 amp but I want the subpanel to handle a 50 amp pool heat pump along with a few other circuits, ie: 20amp mircrowave, 30 amp dock outlet .and a few spare slots.
To make room for the feed , I will have to relocate a 20 amp double breaker from the main to the subpanel also.
First of all, is a 60 amp feed breaker in main panel large enough? Or should it be 70 amp breaker or?
The main panel is now full, but it is a 200 amp service. Also, what wire size should the feeder cable be? Is #6 copper OK?
Any help would be appreciated.

The first question you need to ask is whether your main service panel has the amperage available to feed the sub panel.

To do this, you really should have a load calculation completed on your home electrical services. This should be completed by a licensed electrician.

For example, if you are running at a 175 amp, calculated load, and you try to feed a 70 amp panel you would have an overload condition.

Thanks for the input. The service is 200 amps and the panel is a 20 slot older panel and the usage should be fairly normal for a smaller rambler home.
That's the reason I noted the panel is full and reason for adding a subpanel, although I suppose I could replace the main with a newer 30 space panel but I'd still only have 200 amp service, right?
12 of the slots (circuits) are taken up by double pole breakers, ie: A/C, heat (florida home), range, dryer, water heater and pool pump.
Assuming the total amps are available, my question still is: what size breaker to a subpanel and what's the wire size recommended? More than #6 copper?
I doubt whether even new homes in our area have greater than 200 amp service, but correct me if I'm wrong.
Thanks again for any help!
.

There is no way that I could do a load calculation over the Internet.

It is not based on the number and amperage of the breakers.

You would really need to understand Article 220 of the NEC and that is beyond the scope of this forum.

Thanks - I will have a amp calculation done. but a licensed elec. Contractor suggested a few months ago that rather than keep doubling circuit breakers, he wanted to put in a new larger panel.
From this, I assume the amps were avail. For more circuits.
If so, why wouldn't a subpanel also work the same?
If it would, should it be a 70 amp or 60 Amp breaker and then what wire size? #6 or larger etc.
I will double check the calcuations first though!
Thanks

You mentioned the factors which could be a problem. Electric heat, electric water heater, electric dryer and of course an electric cooking stove. These appliances can add up quickly even with a 200 amp panel. A larger panel may be the way to go to give you room for future expansion. Talk to your electrician about your options.