Whole Home Systems
Dual Tank + Tankless RO
Separate catalytic carbon and softening tanks for bigger homes.
Separate catalytic carbon and softening tanks, for bigger homes and heavier use.
Best for: Larger houses, or where one tank would be working too hard to keep up.
System overview
What the Dual Tank system does differently
Separate tanks instead of one. A dedicated catalytic carbon tank and a dedicated softening tank, each sized for its own job, plus the seven-stage tankless RO at the kitchen sink.
Splitting them matters when one job is bigger than the other - a larger house drawing more water, more bathrooms running at once, or water that needs more carbon contact time than a shared bed can give it. Each stage gets its own vessel and its own full volume of media.
Chattanooga's published hardness is 4.4 grains per gallon (Tennessee American Water, Citico plant, 54-90 mg/L as CaCO3). That is moderately hard - not the 15 or 20 grains you would find in parts of the country, but well above the level where scale starts costing you a water heater.
Component breakdown
Three stages, three jobs
Carbon works the other way round. It does not trade anything - it adsorbs. Chlorine and the compounds that carry taste and smell stick to the enormous internal surface area of activated carbon as water passes through. One gram of it has the surface area of a tennis court, folded into pores. It is why carbon changes how water tastes while a softener does not.
Softening is an ion exchange. Water passes through a bed of resin beads carrying sodium ions; calcium and magnesium - the two minerals that make water hard - swap places with that sodium and stay behind on the resin. Nothing is filtered out in the mechanical sense. The hardness is traded away. When the bed runs out of sodium to trade, the system rinses itself with brine, flushes the calcium to drain and starts again. That rinse is the regeneration cycle.
On a private well the order of treatment matters more than the equipment. Iron and sulfur have to come out before the softening stage, because a resin bed fouled with iron loses capacity and is expensive to replace. Any company that quotes you a softener for a well without testing for iron first is guessing with your money.
Catalytic carbon tank
First in line. Catalytic carbon is a more reactive grade than standard activated carbon and is the right specification where chloramine rather than free chlorine is used.
Softening tank
Second. With the carbon stage ahead of it, the resin only has to do the ion exchange.
The HW800 tankless RO
Seven stages under the kitchen sink, no storage tank.
Two control valves
One per tank, so each regenerates on its own schedule rather than both running off one compromise setting.
Performance specifications
Why two tanks changes the numbers
A single mixed bed shares its volume between resin and carbon. Two tanks give each medium its full volume, which means more contact time on the carbon side and more exchange capacity on the softening side for the same footprint of water going through.
The arithmetic is simple and worth doing before you buy anything. At 4.4 grains per gallon and roughly 60 gallons per person per day, a four-person household puts about 1,056 grains through the system daily, or about 31,700 a month. A 48,000-grain unit therefore regenerates roughly every six and a half weeks on that load. A smaller household goes longer between cycles; a bigger one goes shorter. That interval is what drives your salt use, not the size of the tank.
We publish the numbers our equipment supplier publishes and nothing beyond them. Where you see a flow rate or a rejection figure quoted to two decimal places on a water company's website, ask which test standard produced it. If the answer is not NSF/ANSI, it is marketing.
- Configuration
- Separate catalytic carbon and softening tanks, plus tankless RO.
- Best suited to
- Larger homes, more simultaneous draw, or water needing more carbon contact than a shared bed provides.
- Capacity, flow rate and pressure drop
- Set by the tanks and valves your system ships with. Supplied in writing with your quote.
Drinking water
What you get at the drinking tap
The same seven-stage tankless RO as the Whole Home + Tankless RO system, fed by water that has already been through a dedicated carbon stage and a dedicated softening stage. Feeding an RO membrane pre-treated water is the single best thing you can do for how long it lasts.
Carbon changes how water tastes. RO changes what is dissolved in it. Both, in the right order, is what this system is.
Before you buy
Worth understanding before you buy anything
Bigger is not automatically better. A dual-tank system in a two-person house on moderately hard water is capacity you paid for and will not use. The test at your tap is what decides between this and the single-tank build, and if the answer is the cheaper one, that is the answer you will get.
Catalytic carbon is specified for chloramine. Standard coconut-shell carbon is the right specification for free chlorine. Which one your utility uses decides which is correct for your house - it is worth asking any company which they are quoting and why.
On a private well the order of treatment matters more than the equipment. Iron and sulfur have to come out before the softening stage, because a resin bed fouled with iron loses capacity and is expensive to replace. Any company that quotes you a softener for a well without testing for iron first is guessing with your money.
What you get
Features
- Catalytic carbon + resin tanks
- 7-stage tankless RO
- Written warranty terms with your quote
More photos
A closer look
Also in whole home systems
Whole Home + Tankless RO
Everything above, plus 7-stage RO drinking water at the kitchen sink.
View details →Free water test
Find out what's actually in your water
We'll test your water at your kitchen sink, show you the result, and tell you what — if anything — you need. Free, and there's no system that fits every house.
- Free on-site water test
- Licensed plumber install
- Every price published