I use scented candles, soy candles specifically. Soy candles have less harmful chemicals. Also, I clean my rodent cages with a vinegar mix which helps with the smell. Open windows, good ventilation, etc. I try to move the breeding cages into the basement when temps permit.
Rats smell more when they are stressed so anything that helps them settle down helps keep the smell down.
source : I have twelve rats two ferrets four chinchillas in the upper two bedrooms of our home. Lots of rodents. Rodents everywhere.