From my experience in property rehabilitation, a key strategy for stacking rebates is to start with the federal IRA incentives, as they often set a baseline for what's covered. Then, I look for state-level programs that complement these federal offerings, often having similar eligible upgrades, before finally exploring specific utility rebates. For example, a recent insulation upgrade on one of our properties benefited from the federal tax credit for energy-efficient home improvements, which we then compounded with a state energy efficiency grant available through a local housing authority, and topped it off with a rebate from the utility company for improved attic insulation, which had more stringent R-value requirements. The trick to speeding up approvals and payouts is thorough documentation--take pre- and post-upgrade photos, keep meticulous records of all invoices and contractor certifications, and ensure your contractors explicitly list the efficiency ratings of installed products on their invoices. This proactive approach minimizes back-and-forth and demonstrates adherence to all program requirements upfront.
One tactic that's worked for my clients is applying local utility rebates first since they tend to have limited funds and get awarded on a first-come, first-served basis, then layering on state-level incentives, and finally claiming the federal IRA credit on our taxes. When we replaced an old furnace with a cold-climate heat pump last winter, completing a utility-approved before-and-after blower door test sped up our rebate checks because it gave every agency the performance data they needed up front. That simple step can save weeks of back-and-forth and help everyone involved get paid faster.