Have you ever tried to refinance your investment property, which you rent out room-by-room? This is tricky because banks often prefer homes with a single tenant versus multiple tenants. Find out how you can still appraise your property when you rent out room-by-room.
Find recent sales in your area with similar number of bedrooms, bathrooms, and square footage. This should give you a baseline of how much your property should appriase for. However don't just settle for this baseline. Also estimate what kind of rental income you could get if you were to rent out rooms short term or long-term.
Do a search of AirBnb listings in your property's area to see how much short-term room rentals are rented for. This should give you an upper bound of your rental income which you could expect on a room-by-room basis.
You can check out craigslist.com, spareroom.com, or other sites which list rooms for rent. You may have to dig through multiple listings to filter out the ones that are comparable to your property.
If you want to save time, you can use the free room rental estimator, Rentalios! You can get room rental estimates for your property and if you sign up, you can get rental reports tailored to your property.