How to Install a Tankless Water Heater (Decision Guide)
Tankless conversion is great for some LA homes — but only if you address gas line sizing, peak flow needs, and hard-water scaling.
TL;DR
Tankless water heaters save space, deliver endless hot water, and last 18+ years (vs 10–12 for tank). But they require a 3/4″ gas line (most pre-1985 LA homes have 1/2″), proper sizing for peak demand, and a softener or annual descaling for hard SFV water. Total install in LA: $2,800–$5,800.
What’s in this guide
- Tankless vs tank: pros and cons
- Sizing for peak demand
- Gas line sizing
- Hard-water considerations
- Installation overview
- Permits and inspection
Tankless water heaters are increasingly common in LA renovations and new construction. They deliver hot water on demand without a 50-gallon storage tank, free up garage/closet space, and last longer than tanks. But the conversion is more complex than a tank-to-tank swap — and getting it wrong leads to lukewarm showers and warranty-voiding scale damage. Here’s the LA-specific decision guide.
Tools & Materials You’ll Need
Tools
- Pro install — these are the materials your plumber will use:
Materials
- Tankless water heater (Navien, Rinnai, Noritz, Rheem are the most common in LA)
- 3/4″ black-iron gas line + fittings (if upgrading from 1/2″)
- Stainless steel exhaust venting kit
- Pressure relief valve
- Isolation valves with descaling ports
- Salt-free conditioner or softener (recommended for SFV hardness)
- Permits ($150–$300 from City of LA or applicable jurisdiction)
Step-by-Step Instructions
Calculate Peak Flow Demand
Add up simultaneous flow rates for your peak usage. Standard rates: shower 2.0–2.5 GPM, kitchen sink 1.8 GPM, bathroom sink 1.5 GPM, washing machine 2.0 GPM, dishwasher 1.0 GPM. A 4-bedroom LA home might run 2 showers + 1 sink simultaneously = 5.5–6.5 GPM peak.
Verify Gas Line Capacity
Tankless units burn 150,000–199,000 BTU at peak — much higher than a 40,000 BTU tank. Most pre-1985 LA homes have 1/2″ gas runs sized for tank water heaters. Tankless requires 3/4″ or 1″ depending on distance from meter and total appliance load. A plumber must measure and verify before install.
Address Hard Water (Critical in SFV)
LA water at 9–12 grains per gallon is moderate, but the SFV at 14–18 gpg is HARD. Without a softener or salt-free conditioner upstream of the tankless, scale builds in the heat exchanger within 18–24 months and the unit fails by year 3–5 (warranty void). Install a conditioner ($895–$2,500) at the same time as the tankless.
Choose Indoor or Outdoor Mounting
Tankless units can mount on exterior walls (no exhaust venting needed — saves $500–$800) or interior (requires stainless concentric exhaust through the wall or roof). Outdoor is simpler but exposes the unit to LA temperature swings. Indoor protects the unit but requires venting work.
Install Isolation Valves with Descaling Ports
Critical: install isolation valves with built-in descaling ports ON THE TANKLESS. These let you flush and descale without disconnecting the unit. Adding them costs $80–$150 at install time; retrofitting later costs $400+. Always install at first fitment.
Pull Permit, Install, Inspect
City of LA requires a permit for water heater replacement (about $150) and gas-line work. Inspector visits to verify gas pressure test, exhaust venting, T&P discharge routing, and electrical (if applicable). Schedule install around permit timeline (3–7 days lead time).
For LA tankless conversions, the math we share with customers is: a properly-sized, properly-conditioned tankless installed correctly costs $4,200–$5,800 and lasts 18–22 years. A 50-gallon tank costs $1,800–$2,500 installed and lasts 10–12 years. Over 20 years you’ll buy 2 tanks ($3,600–$5,000) plus more energy ($600/year × 20 years = $12,000+ if natural gas prices stay flat). Tankless is roughly cost-neutral over 20 years and frees up the storage space. Where tankless DOESN’T pay back: small homes with low simultaneous-flow needs (1–2 person households).
Don’t skip the softener in the SFV
A tankless without water treatment in Northridge, Encino, Sherman Oaks, or Van Nuys will fail in 24–36 months. Manufacturer warranty excludes scale damage. Plan the softener at install time.
Real Scenarios from Our LA Service Calls
Tankless cascade for high-demand home
4,500 sq ft home, 6 bathrooms, peak demand calculated at 8.2 GPM. Single 9.5 GPM commercial tankless was insufficient at peak. Recommended cascade install: two 5.5 GPM Navien units in parallel for 11 GPM total. Cost: $5,200 vs $6,800 for single commercial unit. Better redundancy too — if one fails, the other still provides hot water.
When to Call a Plumber Instead
DIY isn’t always the right call. Bring in a licensed plumber if any of these apply:
- ALWAYS for tankless installs — gas line, venting, and permits require licensed C-36 contractor
- You don’t have at least 3/4″ gas service from the meter
- You’re considering tankless in the SFV without a softener
- You want indoor mounting (venting is complex)
- You’re uncertain about peak demand
Frequently Asked Questions
How much does tankless installation cost in LA?
Standard residential install (5.5–7 GPM): $2,800–$3,800 with existing 3/4″ gas and outdoor mounting. SFV install with gas upgrade and softener: $4,500–$5,800. Cascade or commercial-grade: $6,500–$10,000.
How much will I save on gas bills?
Tankless eliminates standby losses (the energy used keeping a 50-gallon tank hot 24/7). Typical LA savings: $15–$30/month on gas bills depending on usage. Doesn’t fully pay back the upgrade cost — you’re paying for endless hot water and longer service life.
Can I install a tankless myself?
No — licensed C-36 contractor required. Gas-line work, exhaust venting, and permits require professional install. DIY voids warranty and is unsafe.
Will tankless work for my old LA home?
Usually yes, with the gas line upgrade and softener install factored in. Pre-1950 homes sometimes need additional electrical or venting work — get a site evaluation before committing.
How often does tankless need service?
Annual descaling (or every 24–36 months with a softener installed). Filter cleaning every 6 months. Anode rod doesn’t apply (no tank).
Need professional help in Los Angeles?
Same-day service. Flat-fee pricing. No surprise add-ons.
Call (818) 938-8660
