I just moved into a house with an in-ground pool with spillover spa. It has an electric heat pump for pool/spa heating, which I understand is great for extending the pool season. Unfortunately, this setup isn’t very good for heating the spa on demand. From what I understand, it would take hours to heat the spa by 30-40 degrees to make is usable in the colder months. I’m looking for a recommendation to heat the spa only - something that would allow it to heat up quickly for on-demand use (like 30 minutes or so). We do have natural gas at the house and lines in the vicinity of the pool equipment.