Adding insulation is one of the best ways to stop your heater from running constantly. You will notice fewer cold spots and a flatter monthly utility bill once the work is done. A typical top-off job only takes a few hours, meaning minimal disruption to your day.
Aim to book your contractor in late summer. They are usually looking to fill their schedule before the first cold snap hits, which can sometimes get you a better price than waiting until everyone else starts calling in November.
The 0% window is a deadline, not a suggestion. If you still have a balance on the card when the 18 months are up, you will start paying interest on whatever remains at the standard rate. Set an auto-pay for $78 a month to make sure you clear the debt on time.