Serious server rooms have large (and expensive) air-conditioning and filtering systems. Most “server rooms” however are not like that, often it’s just some space in a store-room, sometimes near printers (which are a source of air pollution ).
The servers that are stored in serious server rooms have air filters as a standard feature. For small server installations it’s often a desktop PC used as a server which has no filters (and often lacking other server features such as ECC RAM). Recently Dell in Australia started selling low-end PowerEdge servers for $450 plus delivery (similar machines to the $800 Dell servers I previously blogged about ). Also refurbished machines from HP and IBM can often be purchased at auction for similar prices.
Even if you have a proper server with filters on all air inlets it’s still a benefit to have reasonably clean air in the server area. A few years ago I bought four Sunbeam HEPA  air filters for my home to alleviate allergy problems. I’ve had one running 24*7 in my main computer area for most of the time since then. As well as wanting to keep my machines free of dust I have the extra issue of machines that I buy at auction which often are filled with dust – the process of cleaning them frees some dust in the air and it’s good to have a filter running to remove it.
Excessive dust in the air can prevent cooling fans from operating and cause damage to hardware and loss of data. Of course the really good servers have fan speed sensors that allow the CPU to be throttled or the machine to be halted in case of severe problems. But for desktop machines you often only have the temperature control mechanisms that are built in to the CPU and sometimes machines just start having memory errors when the fan malfunctions and the machine gets hot.
As one of the biggest problems facing server rooms is heat dissipation I decided to measure my air filters and see how much electricity they use (it seems reasonably to assume that all their energy eventually gets converted to heat). I’ve now got a blog page about power use of items related to computers . My air filters take 114W when on the highest speed and 13.9W when on the lowest. Initially I was a little surprised at the figure for the high speed, but then I recalled that the energy required to move air is proportional to the speed cubed. I’ll just have to make sure I don’t leave an air filter on overnight in summer…
I’m now going to recommend such filters to some of my clients. Spending $400 on an air filter is nothing compared to the amount of money that a server failure costs (when you have expensive down-time and pay people like me to fix it).