HEPA Filter

Would like to install a HEPA filter into the home. Was told that there isn't enough room to add one without moving hot water tank.

Measurements

I can add more photos and take measurements if this is helpful.

Existing Furnace

Have no immediate plans to replace the existing furnace. House was built in '99. I'm assuming furnace should be good for a few more years?

Future

Want to make sure which ever HEPA filter we install does not limit us in the future when we "do" replace the furnace and/or water heater. We are planning an addition on the home within 18 mos. That may be a good time to replace the furnace.