Why you want to use a dog room purifier?
Dogs often malt a lot (unless they are a breed that retains its coat and has regular shaves) but even then some dogs, especially dog allergy type dogs can have dander (skin that flakes off and gives owners allergies).
But if you have a dog that suffers from dog allergies from the environment, once you have pinned down what they are by having a blood allergy test, like the RAST tests explained previously on this site, then you will know what you are trying to safeguard your dog from.
For instance my dog has dog allergies mostly kept under control from grass, but he visits dog parks with those grasses each day. His allergies heighten the same time each year, just like mine around the spring flowering season.
However if your dog has allergies to grasses, there is a good chance they have allergies to pollens in general, and maybe house mites etc.
While being rigorous with your cleaning, exposing bedding to sunlight or maybe having a chemical treatment can reduce bed mites you still want to do everything you can in your house to stop your dogs suffering.
PREVENTION is the only way with dog allergies as there are very few ‘cures’. Cures usually involve some form of desensitisation or building up oily skin layers through omega 3, but they only go so far.
THAT is why one of the more expensive but often overlooked options is a house air purifier. If you keep your doors and windows closed a lot, then you will reduce the ingress of tiny pollen particles etc .. However a house is not a sealed unit and needs fresh air for health (and breathing oxygen) so you are going to have to have outside air come in at some stage.
dog allergies hint – USE REAL FILTERS, HEPA ETC
I am not here to sell you a dog allergy unit or any snake oil. This might not be the solution for every one with a dog with a severe dog allergy but you wont know until you try. And the reality is that you wont benefit from a foam filter over your air-conditioning duct. You will have to go all scientific on this one and have a separate unit most likely with a HEPA grade filter used in hospitals etc.
The worst thing you can do is think that you have tried every avenue to relieve your dogs pain, but not actually applied the real effort required to keep your air very clean in parts per million of allergens.