Replacing an old, thin garage door makes a massive difference in how much heat stays inside your house during the winter. Once installed, your garage stays warmer, which keeps the floors above it from feeling like ice and stops drafts from creeping into your living room.
Book your contractor in early autumn before the first cold snap hits, as that is when everyone else starts calling. Aim for three different quotes to ensure you are paying for the quality you need rather than just the first price someone drops on your desk.
The 18-month window is a deadline, not a gift. If you have not paid off the full $1750 by the end of that period, you will start paying interest on whatever remains, which gets expensive quickly.