Box Springs and Foundations
Mattress Set or Mattress Only?
What is the value of a box? When shopping for a new mattress should you need to buy a new box, or can you use your old box? Is using a platform bed as good as using a box?
All of these are good questions, and the answer may vary. Most boxes these days are just fabric-covered height. They have wooden slats across the top; oftentimes there will be cardboard over the slats. The few companies that still use coils or metal in their boxes use a rigid structure with little to no give. Therefore, a box is merely height to hold a mattress on a frame. This is one of the reasons platform beds have become more popular over the years. As boxes became an unnecessary part of the support system, people have chosen to save money by selecting frames that no longer require a box.
It used to be that boxes were an integral part of that "support system". If you go back far enough in the history of mattresses, you'll find that batting materials like hay, wool, and cotton were the sleep surfaces of choice for most people (nowadays, we would liken these beds to futon mattresses). Back then coil boxes would provide responsiveness to a sleep surface that was generally quite firm. As mattress companies became more developed, coil systems were inserted into beds to increase their comfort life. These heat-tempered coils were able to maintain their shape for up to 2 million compressions, whereas batting materials compressed fairly quickly.
With coils now being part of the mattress, the coil boxes became a liability to mattress companies. The number of coils used in box springs was not numerous enough to handle the weight of a mattress plus people combined; and mattress companies were more likely to have warrant-able sags to mattress sets they sold. Often times, people needed to insert plywood between the mattress and box to firm up their sleep surface. When people didn't firm up the bed themselves, sags in low coil count boxes led to problem for mattress manufacturers and consumers alike.
So mattress companies changed. Boxes are now manufactured with little to no give so that sags are less likely to be a result of the box, and are sometimes an unnecessary purchase.
If you are now in the market for a new bed, and your bed frame requires the use of a box, do you need to buy a new one?
Unfortunately, you may. Mattress warranties require that you put the mattress on good support system. Platform beds are almost always okay, but old box springs generally aren't. As I said before, these old support systems can develop sags, and that will telegraph through, and potentially even damage a new mattress. If your old box has a slatted wood top and no give, then you should never need to replace it. These platform boxes are a permanent solution; and essentially all mattresses are okay on these.
Then why did the salesperson tell me I have to replace my box, or that it would void my warranty?
It may be that the salesperson doesn't know; or it could be that a rare mattress company has a unique policy. A platform box is equivalent to a platform bed. If there is center support under the middle of the box or mattress, you will meet the requirements for nearly all companies. If you are using a box, anything over a twin or full size should have center support; if it's a platform bed even a full needs that support.