Quick Answer: The isolation valve kit is the accessory that makes tankless maintenance possible at all — without one, you can’t flush the heat exchanger, and most manufacturers treat annual descaling as a warranty condition. For a standard 3/4-inch residential install, the Webstone 44443WPR Isolator EXP E2 (about $118 at Home Depot) is the safest default: full-port forged brass valves, hi-flow hose drains, and a built-in 150 PSI pressure relief valve. Want a heavier valve body with push-to-connect flexibility instead of sweat or threaded ends? The Watts LFTWHG2-FT-HC-RV (around $196) adds VersaFit connections. On a tight budget, the Eastman 60204 (about $60) covers the same core function with tethered drain caps.
Most people shopping for this part are already past the “what is a tankless water heater” stage — they own one, and either the installer skipped the isolation valves to save cost, or a service tech just told them descaling isn’t possible without a set. That second scenario is more common than it should be: Rinnai’s own installation bulletins instruct the installing plumber to specifically flag it in writing to the homeowner if isolation valves were not installed on the job, which is the manufacturer’s way of saying this isn’t a nice-to-have. This roundup compares the four kits worth buying, in order of who each one fits.
The rule that decides everything: full-port flow and a built-in relief valve, non-negotiable
Every kit worth buying uses full-port ball valves — a bore as wide as the pipe itself, so the valve doesn’t throttle flow when open — and includes a 150 PSI pressure relief valve built into the cold-side body. A reduced-port valve can measurably choke flow on a system already running close to its rated GPM, and the relief valve is the same safety function a T&P valve serves on a tank heater, just sized for a tankless unit’s higher BTU input (199,000-200,000 BTU rated). Beyond that baseline, the real decision is connection type — sweat (copper), threaded (NPT), or push-to-connect — and whether you need heavy-duty flow or just a functional isolation point. For the annual maintenance these valves exist to support, see our tankless water heater descaling guide and our best tankless water heater flush kit picks for the pump-and-bucket half of the job.
Our top picks at a glance
| Kit | Connection | Port | Relief Valve | Price |
|---|---|---|---|---|
| Webstone 44443WPR Isolator EXP E2 | 3/4" IPS threaded | Full port | 150 PSI/200K BTU | ~$118 |
| Watts LFTWHG2-FT-HC-RV | 3/4" FNPT + VersaFit push-fit | Full port | 150 PSI | ~$196 |
| Eastman 60204 | 3/4" FNPT union x FIP | Full port | 150 PSI | ~$60 |
| Watts 0100156 | 3/4" copper sweat | Full port | 150 PSI | ~$100-140 |
1. Webstone 44443WPR Isolator EXP E2 — Best Overall
Webstone 44443WPR 3/4-in. Isolator EXP E2 Tankless Water Heater Valve Set
- Hot and cold valves are color-coded and both carry hi-flow hose drain ports, so a descaling pump connects directly without adapters — the whole point of buying a kit instead of generic shutoff valves.
- Union connections at the water heater end mean the entire valve assembly unscrews for service or replacement without cutting or re-soldering pipe.
- The most widely stocked tankless-specific valve kit across Home Depot, SupplyHouse, and plumbing wholesalers — parts and compatible fittings are easy to find years later if something needs replacing.
Get your tankless heater and fittings in two days — try Amazon Prime free for 30 days.
This is the default buy for the same reason Webstone shows up across so many OEM parts lists: it’s a purpose-built tankless kit, not a generic valve pressed into service, and the union fittings make future maintenance a five-minute job instead of a re-plumb.
2. Watts LFTWHG2-FT-HC-RV — Best for Push-to-Connect Installs
Watts LFTWHG2-FT-HC-RV Tankless Water Heater Valve Set with VersaFit
- VersaFit technology lets the valve connect via push-fit, threaded, or press connection depending on what's already run to the heater location — useful on a retrofit where the existing stub-out isn't a clean threaded or sweat connection.
- Watts' kit is built to replace what the company describes as up to 18 separate fittings and connections in a typical field-assembled tankless supply setup, which is the real cost justification for the higher price versus a basic kit.
- The premium price puts this in "install once, don't revisit" territory rather than the budget-conscious pick — reasonable if you're paying a plumber for labor anyway and want to minimize a second service call.
Choose this over the Webstone kit specifically when your rough-in doesn’t line up cleanly with threaded or sweat connections — the VersaFit flexibility is worth the roughly $80 premium in a retrofit, less so on new construction where you’re setting the connection type anyway.
3. Eastman 60204 — Best Budget Pick
Eastman 60204 Tankless Water Heater Service Valve Kit
- Roughly half the price of the Webstone kit while covering the same non-negotiable core: full-port valves and a built-in relief valve rated for tankless BTU input.
- Drain valves are tethered with caps rather than open hose-thread ports, a small step down in convenience from the Webstone's hi-flow hose drains but functionally adequate for annual descaling.
- 4.2 out of 5 stars across Home Depot's own listing reviews — the tradeoff buyers report is fit-and-finish, not function; it isolates and drains correctly, it just feels less heavy-duty in hand than the Webstone or Watts kits.
If your goal is simply to stop being unable to descale the unit — not to future-proof the install with premium hardware — this is the pick. It meets the same warranty-relevant baseline as the pricier kits.
4. Watts 0100156 — Best for Copper Sweat Installs
Watts 0100156 3/4-in. Copper Tankless Water Heater Valve Installation Kit
- Built specifically for copper supply lines rather than threaded or PEX stub-outs, so the connections are sized for solder rather than requiring a threaded transition fitting.
- Same full-port and relief-valve baseline as the FNPT kits above — the only real difference is the pipe connection method, which matters if your existing rough-in is copper.
- Worth checking against your specific plumbing before ordering: mixing sweat and threaded kits mid-project usually means buying transition fittings you didn't budget for.
Pick this one first if you already know your supply lines are copper — it saves buying threaded valves and then a set of sweat-to-threaded adapters to make them fit.
How to choose
- Standard 3/4-inch threaded install, no special requirements: the Webstone 44443WPR is the safe, widely-stocked default.
- Retrofit where the rough-in doesn’t cleanly match threaded or sweat: the Watts LFTWHG2-FT-HC-RV and its VersaFit push-to-connect flexibility earns its higher price.
- Budget-conscious, DIY, or a rental property where premium hardware isn’t the priority: the Eastman 60204 covers the same functional baseline for about half the cost.
- Existing copper supply lines: the Watts 0100156 sweat kit avoids extra transition fittings.
- Unsure whether your current install even has isolation valves: look for two shutoff valves with hose-bib style drain ports directly at the heater’s water connections; if you see the supply lines running straight into the unit with no valves, you don’t have them, and neither does your ability to descale on schedule.
The bottom line
An isolation valve kit is not an optional upgrade — it’s the part that makes the annual descaling nearly every tankless warranty requires physically possible. The Webstone 44443WPR Isolator EXP E2 is the right default for most 3/4-inch threaded installs at around $118. Step up to the Watts LFTWHG2-FT-HC-RV (around $196) for push-to-connect flexibility on an awkward retrofit, or down to the Eastman 60204 (around $60) if budget is the priority and you just need the functional baseline. Whichever you buy, confirm it has full-port valves and a built-in 150 PSI relief valve — every kit here does, and nothing without both belongs on a tankless unit.