At 4 weeks and with your room temperature set at what you have it, a heating pad is no longer needed. Just a nice comfy bed with some blankets placed away from any possible drafts. I usually use "mom" as the key in deciding when to start the weaning process, which is normally around 5 or 6 weeks but the pups are usually not totally weaned until 7-8 weeks.
Congrats on your litter......enjoy them, they don't stay little for long.
