It'll help. Ask for some customer references, maybe someone with a similar house. But it could also cause other problems. Older houses are naturally leaky and that helps keep them manage mold/mildew and radon. Your water heater and furnace could also backdraft. So that's something to consider. Modern houses are basically sealed inside a plastic bag so you need active mechanical ventilation to keep things in order.

If you have a really old house make sure you don't have vermiculite insulation which might make things way more expensive cause it likely has asbestos in it. Apart from that you can also DIY it but it's messy. Your state may offer incentives for doing it too.

https://www.energystar.gov/campaign/seal_insulate/attic_air_...