SFR is an important consideration if you want the softener sized correctly. Even without that data you're in the 2.5 cube ballpark, but I'd have to know the SFR in order to size correctly.

It's never bad to size for the highest hardness test.

You want a pressure gauge before and after the BB so you can see the pressure loss across the filter element and KNOW when it's time to change the element.. that is IF you need a BB filter at all and what it is filtering.

Red/orange seediness can be indicative of iron in the water so if you're testing with a DIY kit or the sellers are testing do the smart thing and get a comprehensive water test from a local certified independent lab.

A water treatment pro should be able to give you the specifications for every component in the softener IF you ask. If they can't or won't then they are not professionals and you should avoid them.

Thanks, Lurker.

I'll gather the SFR next time I'm at the house (we haven't moved in yet).

Company #3 did test the iron, and it didn't come back with anything. The report from the lab reported (what I consider to be) trace amounts (Iron: Both 2 and 3 did suggest a BB after seeing the sediment and its size in the toilets. 2 suggested a 10", 3 a 20". Not sure if either has an advantage over the other? Maybe longer media life of the larger one?

Suggesting a BB housing is one thing but what matters is the element inside. What element are they suggesting?

20" will go longer between changes and flow more than the 10". Once you know the SFR then we know what the required flow rate is for both the softener AND a BB filter.

I'd get the lab to re-test for iron and manganese.

Was able to get to the house today to test the SFR. I did it from a tub and a hose bib.

Tub = ~5 gpm
Hose bib = ~10 gpm

After reading a few more threads it seems that my SFR might be on the lower side. The question is, does a lower SFR still warrant a higher capacity system, or is that recommendation based on anticipated usage?

Correctly sizing a softener is based on water conditions, water usage, and plumbing considerations.

If the required peak SFR exceeds the capability of the specific volume of resin hardness will leak through.

When sizing a softener correctly it is not uncommon to go up a size to accommodate SFR when necessary.

Since your hose bib SFR = 10 the correct softener based on your water conditions and usage will have more than enough flow rate.

Makes sense, thanks! So I guess a 2.5 cu ft softener is still the way to go.

My 2.5 cu ft softener was installed yesterday. There wasn't enough vertical space in the basement rafters for an air gap so the installer put in a check valve before t-ing into the waste line. Is a check valve a suitable alternative for an air gap?

"...the installer put in a check valve before t-ing into the waste line. Is a check valve a suitable alternative for an air gap?"

Unless your local plumbing code allows it, no. A check valve is a mechanical device that can fail open allowing cross-contamination. It can also fail closed and block the softener drain line.

The installer should know that if he is a licensed plumber and in your locale a permit may be required which obviously wasn't pulled.

There are a variety of ways to air gap a softener drain line ( www.airgap.com ) to a standpipe with a P trap off a waste line

I was afraid of that. I believe permits are required and one wasn't pulled. I'm feeling a little anxious now since we plan on having the basement finished in a couple of months, which will obviously be permitted and inspected.