Having 5 Medium size dogs in a average 3 bedroom Carpeted house, (carpets could do with changing as they have been down many years and we all know fabric absorbs)it can get a bit doggy according to those who aren't if you know what I mean. 

I don't mean that urine smell that some canine homes can suffer if they have
males that mark, or incontinent oldies, I mean just the generally slightly musty
breath and bum gas odours that our friends can produce.

Are Air Purifiers worth having?  In summer I just try and get plenty of air
in the place with open windows, but if I go out to avoid any neighbour
problems all windows are shut, and 5 dogs confined to the kitchen can whiff
a bit.

Personally I use Bicarb of soda, it will not do the animals any harm and you can mix in a few drops of something like lavender oil if you want a nice smell as opposed to a neutral smell. Sprinkle over carpets or soft furnishings preferably brushing in and leave for as long as you can or over night, then vaccum off. It works a lot like shake and vac but is much cheeper and involves no nasty chemicals.

we have one that comes on overnight, it does seem to help and also makes your dust much finer