Plenty of homes do not have an open spot for a softener. The water heater, the furnace, a washer, and a wall are already crowding the same corner. The right unit is the one you can install, operate, and service in the space you have, with the connections and access the manufacturer requires. Measure the room before you fall for a model.
Measure the footprint and the working room
Note the width and depth of the unit, then add room on each side for the plumbing connections and for any work you will need to do. The control valve and the salt fill area need clear space above and in front. A bag of salt has to be lifted and tipped into the tank, so a narrow gap between the tank and a wall can make refilling harder than it should be.
Also check the height. Measure to the ceiling, and to any pipe or duct that runs overhead. Allow for the lid and any fill opening.
Plan the inlet side around the water heater
In most installs, the softener sits on the main line before the water heater, so that softened water reaches the heater and the rest of the house. Look at where the main shutoff is, where the line enters the house, and where the heater connects. The softener has to tie into that line with enough room for the bypass, the shutoff valves, and a drain connection. If the heater is close to the wall, confirm the plumber can make the connection without forcing pipe.
Check the drain and the power
The drain connection needs to be reachable and at a workable height, so confirm there is a standpipe, a floor drain, or another approved drain point within reach of the hose. Confirm that a grounded outlet is close enough to power the valve without a long extension cord. Do not plan to run a cord across the floor of a utility space.
Look at the access route
Measure the doorway and any turns between the outside door and the utility space. Tanks are heavy, and the delivery team has to get the unit in whole. If the door is narrow, ask the provider how they will move the unit, and whether they need to remove a door or a casing to do it.
Floor and level
The tank should sit on a floor that is solid and level. Check for cracks, a soft spot, or a slope toward a drain that could cause water to pool under the unit. A small level and a tape measure are enough to check this before you talk to anyone.
What to bring to the provider
Bring the measurements, a few photos of the space from several angles, and the location of the main line, drain, and outlet. A provider who asks for these before quoting is planning the install. One who quotes without seeing the space may leave you with a surprise on install day.
For a full checklist on the buying process, see the Missouri Water Softener Buyer's Guide.