The long big diameter housing costs more than the short one and buys roughly double the capacity in the same diameter. Whether that is worth paying for is an arithmetic question with a different answer in different houses, and it turns on how dirty the water is and on what the cartridge is being asked to do.
Where the payback is clearest
On dirty water, because the change interval is what dominates. A household changing a short cartridge every couple of months on well sediment is spending both money and an afternoon each time, and halving that frequency is a real saving in both. The cost per cartridge for the long version is not double the short one either, so the cost per volume treated falls as well. On this water the longer housing usually pays for itself within a year.
Where it is qualitatively different
Carbon, where the gain is not just interval. Chlorine removal depends on contact time, which is bed volume divided by flow, so doubling the length doubles the contact and moves a carbon cartridge from partial removal towards something close to complete at household flow. That is not a convenience improvement, it is a performance one, and it means a short housing on a whole house carbon duty is underperforming rather than simply needing changing more often.
Where it does not pay
On clean municipal water with a light sediment load, where a short cartridge already lasts a long time and halving an already infrequent change saves very little. Where clearance below the housing will not accommodate the longer sump, in which case the question is moot. And where one person has to service it alone, since a full long sump is heavy and awkward enough that the practical cost of each change goes up rather than down.
The arrangement that often wins instead
Two short housings in series, staged coarse then fine, will usually outlast a single long housing on sediment duty, because the cheap coarse cartridge absorbs the bulk and the fine one lasts several times longer than it would alone. Two short housings also fit where one long one does not. For carbon, though, length wins and staging does not replace it. Our whole house filter guide covers staged layouts and cartridge selection.
Questions people ask about 20 x 4.5 water filter
Is the long housing worth the extra cost?
On dirty water, usually within a year, since it halves the change frequency and costs less per volume treated.
Does length matter more for carbon?
Yes, and qualitatively. Chlorine removal depends on contact time, so double the length is close to double the removal.
When is the short version better?
Clean municipal water with light sediment, tight clearance below the housing, or where one person services it alone.
Would two short housings be better?
For sediment, often yes, staged coarse then fine. For carbon, no, since contact time comes from length in a single bed.