Direct answer: HALO sizes each ION 2.0 Plus by the maximum flow at which it conditions water. The ION-6 (¾-inch FIP, 6 gpm) is the water-heater model. The ION-9 (1-inch, 9 gpm) is listed for whole houses with one or two baths, the ION-12 (1-inch, 12 gpm) for three or four baths, and the ION-20 (1-inch, 20 gpm) for four to six baths. The ION-35 and ION-50 (1½- and 2-inch) are for multi-unit buildings. Smaller ION-H and ION-GH versions serve humidifiers and hose bibs. None of them removes hardness: HALO’s own FAQ says water will not test soft after installation, and HALO states the ION is not tested or certified by WQA.
Publisher boundary: Water System Guide is an independent research publisher, not HALO or a HALO dealer. Specifications and claims on this page come from HALO documents dated December 2024 to 2025, reviewed October 8, 2026. HALO’s descriptions of how the ION works and what it does to scale are the manufacturer’s claims. We have not tested them, and we report them as claims.
HALO ION 2.0 Plus specifications by model
From the ION 2.0 Plus spec sheet, page 2. The August 2025 installation sheet, page 2, repeats the same table.
| Model | Dimensions | Fittings | Use case in HALO’s table | Maximum flow |
|---|---|---|---|---|
| ION-H | 1.125” D x 5” L | ¼” compression | Humidifier | 6 gallons per hour |
| ION-GH | 1.25” D x 7.5” L | Hose bib | Plant watering | 5 gpm |
| ION-6 | 1.75” D x 9” L | ¾” FIP | Water heaters | 6 gpm |
| ION-9 | 2.25” D x 9.25” L | 1” FIP | Whole house (1–2 bath) | 9 gpm |
| ION-12 | 2.25” D x 13” L | 1” FIP | Whole house (3–4 bath) | 12 gpm |
| ION-20 | 2.25” D x 17” L | 1” FIP | Whole house (4–6 bath) | 20 gpm |
| ION-35 | 2.50” D x 16” L | 1.5” FIP | Whole house (multi-unit) | 35 gpm |
| ION-50 | 2.50” D x 16.50” L | 2” FIP | Whole house (multi-unit) | 50 gpm |
HALO’s sheet says each model “is sized according to the maximum flow rate at which it will condition the water most effectively,” and that the ION “does not restrict water flow.” The bathroom counts are HALO’s shorthand for flow. If your household runs several fixtures at once, compare your measured or estimated peak flow with the gpm column. Our whole-house flow rate calculator can help.
ION-6 vs ION-9: water heater or whole house?
The ION-6 and ION-9 are the two most-searched sizes, and they solve different problems.
- ION-6: ¾-inch FIP and 6 gpm, listed for water heaters. HALO’s installation diagrams show an ION on the cold inlet of a tankless heater and on a tank heater, including set-ups with a recirculation loop (spec sheet, page 2).
- ION-9: 1-inch FIP and 9 gpm, listed for whole houses with one or two bathrooms. HALO’s diagram shows a whole-house unit on the main line where water enters the household.
A water-heater model protects what is downstream of the heater inlet. A whole-house model goes on the main. If your quote lists both, ask what each one is meant to protect.
ION-12 vs ION-20 for larger homes
The ION-12 and ION-20 share the ION-9’s 2.25-inch diameter and 1-inch FIP connections. They differ in length (13 and 17 inches) and maximum flow (12 and 20 gpm). Because all three use 1-inch fittings, the pipe size does not decide between them. Peak flow does. The ION-35 and ION-50 step up to 1½- and 2-inch fittings and are labeled multi-unit.
Installation: what HALO’s sheets require
HALO’s ION sheets list these installation features:
- No drain line, no electricity and no chemicals. HALO describes the unit as maintenance-free.
- Vertical or horizontal installation. This appears on the August 2025 sheet.
- Dielectric unions are no longer needed unless dissimilar metals are present. HALO’s “pro tip” says this is to ensure electrolysis is not an issue during soldering.
- Recirculation loops. The HALO 5 warranty requires a secondary HALO ION on each recirculating loop when a recirculation pump is in use. See our HALO 5 installation guide.
Does the HALO ION soften water?
No. HALO’s FAQ asks, “Will the water test soft after the system is installed?” and answers “NO.” It explains that calcium is still present “in an altered suspended state.”
HALO describes the ION as using “multi-reversing polarity permanent magnetic fields” to keep hardness minerals suspended rather than forming scale. It claims the conditioned water “will dissolve existing scale over time” (HALO ION product page). These are manufacturer claims. The HALO 5 spec sheet, page 1, states that “The Halo ION 2.0 Plus scale inhibitor is not tested or certified by WQA.” It adds that the media and ION are certified to NSF/ANSI/CAN 61 (material safety) only when used in the HALO 5 series.
Because a hardness test cannot confirm the result, agree on another check with the seller before buying. For example, inspect a water heater or fixture over time. Our water conditioner vs water softener comparison explains the difference in treatment, and salt-free water conditioners covers the category.
HALO’s FAQ also says that, in a four-person home, the water heater will need flushing three to four months after installing a HALO solution with a HALO ION, because the ION dissolves existing scale. Ask the installer whether that flush is included.
What warranty does the HALO ION have?
HALO’s documents state the term three ways:
| Document | Warranty statement |
|---|---|
| ION 2.0 Plus spec sheet, December 2024 | Page 1: “25 year warranty,” “Parts AND labor on the first 10 years!” Page 2: “a 10 year manufacturer’s parts and labor warranty” |
| ION installation sheet, August 2025 | “a 25-year manufacturer’s warranty with parts and labor included for the first 10 years” |
| ION 2.0 Plus warranty certificate, 2025 | 25 years on the magnetic bar for manufacturer’s defects. For the first 10 years: magnetic bar, housing and labor, with a $125 labor / $50 part allowance on approved claims |
The 2025 certificate is the most specific and most recent document. It also says the owner must fill out and return the certificate by mail or fax to HALO in Carlsbad, California, to make the warranty effective. Replacement requires the defective unit, prepaid replacement freight and proof of purchase. HALO’s FAQ separately lists “10 years on the HALO ION 2.0 Plus” as part of the HALO 5 warranty. Our HALO warranty guide compares this with HALO’s other products.
Questions for the seller
- Which ION model is proposed, and what peak flow was it sized for?
- Where will it go: the main line, a water heater inlet or a recirculation loop?
- Does the price include returning the warranty certificate and a water heater flush?
- How will we judge the result, given that a hardness test will not change?
Frequently asked questions
What size HALO ION do I need?
HALO sizes the ION 2.0 Plus by maximum flow. Its table lists the ION-9 (9 gpm) for one to two bathrooms, the ION-12 (12 gpm) for three to four and the ION-20 (20 gpm) for four to six, with the ION-6 (6 gpm) for water heaters. Compare your home’s peak flow with those ratings.
What is the difference between the HALO ION-6 and ION-9?
The ION-6 has ¾-inch FIP fittings and a 6 gpm maximum flow and is listed for water heaters. The ION-9 has 1-inch FIP fittings and a 9 gpm maximum flow and is listed for whole houses with one or two bathrooms.
Will my water test soft with a HALO ION?
No. HALO’s FAQ says the water will not test soft because calcium and magnesium are still present. HALO says the ION conditions those minerals; it does not remove them.
Does the HALO ION need electricity or a drain?
No. HALO’s spec and installation sheets say the ION 2.0 Plus needs no drain line, no electricity and no chemicals, and that it does not restrict water flow.
Sources and review scope
- HALO ION 2.0 Plus spec sheet, dated December 5, 2024; retrieved October 8, 2026. Pages 1–2.
- HALO ION installation sheet, dated August 4, 2025; retrieved October 8, 2026.
- HALO ION 2.0 Plus warranty certificate, 2025; retrieved October 8, 2026.
- HALO ION 2.0 Plus product page and HALO FAQ, retrieved October 8, 2026.
- HALO 5 spec sheet, Rev.3326, page 1 (WQA scope note), retrieved October 8, 2026.