Why are DC filters round?

[Doug Hobkirk]

I know there must be problems with this idea, but I am curious what they are. And since there are about a dozen active threads on DC's...

Fine mesh cloth bags and canisters rule the DC world, even on cyclone systems that eliminate most of the waste. The filters on cyclone systems pretty much have to cope only with dust - correct?

Canisters are pretty expensive. Why wouldn't a column with high quality rectangular furnace filters work?
Design so filter area is more than a canister.
The housing should be pretty easy to make, including a clean-out door.
A 6-sided design would diminish trapping dust in the corners.
The filters would be less expensive since they're easier to make, easier to ship and store, and made by the million.Thanks for humoring me by considering my questions.

[alex grams]

Cylindrical filters give even flow throughout the perimeter of the filter in respect to the rest of the filter at that height.

A rectangular filter would have dead flow spaces in the corners that, while maybe having an overall larger area, would have 'hotspots' in the filter that get a larger amount of flow at a certain point along its height as compared to other areas of the filter at the same height.

Plus, you only have to manufacture 1 seam in a cylindrical filter, while with a rectangular filter, you would have to make 4.

[Cliff Rohrabacher]

Cost and efficiency.
If you build your own you can use any geometry you please.

[M Toupin]

It all comes down to surface area... for example, the Wynn 35A274BLOL filter for the HF conversion (http://www.wynnenv.com/35A_series_cartridge_kit.htm) has 274sq ft of filter area in a 17.5" X 23" package. If you were to build a box from furnace filters your box would be roughly 10 foot X 7 foot on each side. That's a lot of space to get the same surface area as a canister. Even if you could build a filter box that big and come up with an effective method of sealing the filters in, you'll still need to find furnace filters that filter to .5 micron or so. Check prices on MERV11 furnace filters.

Bottom line - a quality canister filter costs a lot less than 275 sq foot of MERV11 furnace filters.

Mike