Tank-to-Tankless Conversion Considerations Reference

Why this matters

Customers ask about tankless water heaters frequently. Marketing says endless hot water + energy savings; reality is more nuanced. Conversion from tank to tankless has hidden costs + considerations many homeowners don't know. The tech who can explain honestly helps the customer make the right decision for their home. This is the field card.

Tank vs tankless basics

Storage tank:

• 30-80 gallons of hot water stored
• Heated continuously (standby loss)
• Recovery time after heavy use
• 8-12 year lifespan typical
• Lower upfront cost

Tankless (on-demand):

• Heats water as it flows
• No storage
• "Endless" hot water (if sized correctly)
• 15-20+ year lifespan
• Higher upfront cost
• Energy efficient

Honest comparison

Tankless advantages:

• No standby heat loss (more efficient)
• Longer lifespan
• Doesn't run out (limited only by flow capacity)
• Compact (wall-mounted; saves floor space)
• Less risk of catastrophic flood (no tank to fail)

Tankless disadvantages:

• High upfront cost (equipment + installation)
• Often requires gas line upsize OR electrical service upsize
• Requires venting (different from tank)
• "Cold sandwich" effect (cool water in pipes when restarting)
• Minimum flow rate to activate (low flow = no hot water)
• Limited simultaneous use (capacity matters)
• Hard water + scale = maintenance + reduced life
• May not deliver "endless" if undersized
• Annual maintenance needed (descaling)

Sizing tankless

Critical for satisfaction:

Flow rate (GPM at temp rise):

• Manufacturer specs GPM at 70°F rise typical
• Need to support simultaneous uses

Simultaneous uses:

• 2 showers: ~5 GPM combined
• Shower + dishwasher: ~3.5 GPM
• Shower + laundry: ~4 GPM
• 3 simultaneous uses: ~7 GPM

Temp rise calculation:

• Incoming water temp (40°F winter, 70°F summer typical)
• Desired hot water temp (110-120°F)
• Rise = desired - incoming
• Tankless rated GPM decreases as rise increases

Cold-climate winter + multiple uses = larger unit needed. Many customers undersized; disappointed.

Gas tankless

Most-common conversion:

Gas requirements:

• Higher BTU than tank (150,000-200,000 BTU vs 35,000-50,000 tank)
• May require larger gas line (1" instead of 3/4")
• May require larger meter
• Gas line upgrade can be a significant add-on cost

Venting:

• Direct vent (sealed combustion) most common
• Concentric (intake + exhaust in one pipe)
• OR separate intake + exhaust
• Code-compliant clearance
• Different than tank (vent to roof)

Combustion air:

• Sealed combustion takes air from outside
• Doesn't need utility room "make-up air"

Pilot OR electronic ignition:

• Modern tankless = electronic
• Standby gas use minimal

Electric tankless

Less common; specific situations:

Electric requirements:

• High amperage draw (multiple 240V circuits typical)
• 100+ amp service may not support
• May require service upgrade
• Whole-house electric tankless can require 200A+ service
• Electrical service rework can be a major add-on cost

Where electric tankless works:

• Point-of-use (single fixture)
• Small homes
• Auxiliary use (under sink hot water)
• Off-grid OR where gas not available

Where electric tankless fails:

• Cold-climate whole-house (needs huge wattage)
• Old electrical service
• Heavy simultaneous use

Water quality impact

Hard water + scale build-up affects tankless:

• Heat exchanger fouls
• Reduced efficiency
• Eventually requires descaling

Hard water (US average + harder regions):

• TX, AZ, NV, FL, IN, OH, others
• Annual descaling required
• Water softener significantly extends life
• Without softener: 5-7 year heat exchanger life (vs 15-20 with soft water)

Customer in hard water area should plan for:

• Water softener install (if not present)
• Annual descaling service
• Filter cartridge changes

Conversion installation steps

For tank to tankless conversion:

1. Site assessment:

   • Existing gas line size
   • Existing electrical service
   • Vent path available
   • Water lines + connections

2. Remove existing tank:

   • Drain
   • Disconnect plumbing + gas + electric
   • Haul away

3. Install tankless unit:

   • Mount to wall (often near old tank location, OR rerouted)
   • Connect water lines (often with hot water recirculation prep)
   • Connect gas (with upsized line if needed)
   • Install vent

4. Electrical:

   • Power circuit for tankless (often 120V receptacle)
   • GFCI / AFCI per code

5. Commissioning:

   • Fill + bleed
   • Combustion test
   • Verify flow + temp at fixtures
   • Customer walkthrough

Realistic costs

Tank water heater replacement (50-gallon gas tank): typically the lowest cost option.

Tankless installation (gas tankless, conversion from tank): typically 2-4x the cost of a tank replacement, depending on gas line upgrade + venting needs.

Customer needs to know honest total cost, not just equipment price.

Realistic payback

Energy savings:

• Tankless typically cuts operating cost roughly in half vs a tank
• Annual savings is modest in absolute terms

Upfront cost difference: tankless conversion is meaningfully more expensive upfront.

Payback: 15-30+ years. Often longer than equipment life.

Tankless makes sense for:

• Customer wants endless hot water (lifestyle preference)
• Compact space requirements
• Long-term homeowner (will see benefit)
• Older system needs replacement anyway

NOT for:

• Pure ROI (often doesn't pay back in lifespan)
• Quick flip / sale planned
• Hard-water area without softener
• Limited utility upgrades possible

Common customer misconceptions

"Tankless saves me money immediately":

• Operating cost lower; upfront much higher
• Payback period usually exceeds equipment life

"Endless hot water":

• Only if sized correctly
• Cold-climate + multiple uses = may not deliver

"They last forever":

• 15-20 years typical
• Maintenance required
• Hard water shortens significantly

"Easy DIY install":

• Gas + venting + electrical + plumbing
• NOT DIY (illegal in most jurisdictions)
• Permit + licensed install required

Recirculation considerations

Many homes want hot water immediately at faucets:

Tank with recirculation pump:

• Works
• Continuous pump = energy use
• On-demand pump = better

Tankless + recirculation:

• More complex
• Some tankless have built-in recirculation feature
• Continuous recirculation defeats efficiency (heating + pumping when no use)

If customer wants instant hot water: discuss options upfront.

Hybrid heat pump water heater

Different option:

Heat pump water heater:

• Tank type
• Pulls heat from surrounding air
• Very efficient
• Slower recovery than gas
• Needs warm space (basement, garage)
• $$ upfront but utility rebates often available

References

• DOE Energy Star water heater specifications
• ANSI Z21.10 (water heater safety standards)
• NFPA 54 (National Fuel Gas Code)
• Manufacturer literature (Rinnai, Navien, Bosch, Bradford White, A.O. Smith)
• Manuall internal: Water Heater Sizing, Hot Water System Diagnosis