Whole-house sizing is complete only when an offer meets the treatment need, demand, pressure budget and service constraints together. Use this page to compare quotes on the same evidence, after calculating demand. It is not another bathroom-count sizing chart.
Put each offer into the same matrix
| Requirement | What a usable quote supplies |
|---|---|
| Treatment objective | Exact constituent or outcome and supporting model-specific claim |
| Service flow | Flow at which that treatment claim applies |
| Hydraulic performance | Complete-system loss at your agreed demand |
| Capacity | Rated duty, feed conditions, gallon/time limits and service trigger |
| Service cycle | Backwash/regeneration demand and drainage where relevant |
| Installation | Dimensions, clearance, controls and utility requirements |
| Ownership | Approved parts, replacement costs and responsible service provider |
Keep empty fields marked “not supplied.” A quote should not win because an unknown value was silently treated as unlimited capacity, zero loss or no maintenance.
Work through a comparison
Suppose your agreed demand scenario is 8 GPM. Offer A advertises “12 GPM maximum” but gives no treatment-flow or pressure-loss evidence. Offer B documents the required claim at 8 GPM and supplies the relevant system curve. B is currently more assessable; A needs clarification before it can be compared. That is an evidence distinction, not proof that A is physically inferior.
Now suppose B requires a backwash flow the source cannot deliver. It also fails the proposed installation until that constraint is resolved. A favorable treatment number cannot cancel an unmet service requirement.
Separate capacity units
Gallons of rated contaminant reduction, grains of softening capacity, media volume and dirt-holding capacity describe different things. Do not compare them as though a larger printed number means a larger useful system.
For carbon, use the claim-specific capacity worksheet . For demand, use the fixture-overlap worksheet . Keep actual source-water conditions beside every capacity estimate.
Ask for an acceptance brief
Before ordering, agree what will be checked at commissioning: correct equipment and route, operating conditions, required flushing/sanitation, hydraulic delivery and treatment verification appropriate to the claim. Also agree what happens if the measured conditions differ from those assumed in the quote.
This creates a practical boundary between a seller’s estimate and a supported installation. It avoids treating an upstairs shower complaint as proof of undersizing when the source, regulator, local plumbing or a loaded cartridge could be responsible.
NSF’s standards overview supports matching exact treatment claims. The comparison matrix and worked case are editorial decision tools, not hands-on product test results or a substitute for a qualified system design.
Use the carbon-specific capacity worksheet when the quote includes a carbon tank .