THE SHORT VERSION
- A same-type swap is the cheapest job: same type, same fuel, same spot, reusing the vent, gas line or circuit. Home Depot’s $1,600–$2,400 tank range covers that job, and it says its figures already include permits and code upgrades.
- Conversions cost more because they change the house: a new vent, a bigger gas line for tankless, a 240-volt circuit or panel upgrade for electric and heat pump models, or a chimney liner for the furnace left behind.
- Code items your old setup lacked (expansion tank, seismic straps, drain pan, relief-valve discharge pipe, sediment trap) each add tens to a few hundred dollars, and are set by local code or the manufacturer.
- Hard access and moving the heater add labor: attics, crawlspaces, tight closets and new pipe runs.
- Ask who requires each line item: the code, the manufacturer’s instructions, or you. That one question explains most gaps between quotes.
The cost drivers at a glance
Two quotes for the same 50-gallon heater can be $1,000 apart and both be honest. The difference is almost always work around the heater, not the heater itself. The table lists each driver, what usually sets it off, and who decides whether you need it; the self-check helps you spot them at home.
| Driver | Typical trigger | Who decides |
|---|---|---|
| New or changed venting | Switching to a power-vent, condensing or tankless gas unit; no usable chimney | Manufacturer’s instructions and the fuel gas code |
| Chimney liner or vent resizing | A furnace or water heater leaves a shared chimney | Fuel gas code venting tables; the inspector |
| Bigger gas line | A high-input tankless unit, or adding gas where there was none | Fuel gas code (pipe sized on total connected load) |
| New circuit or panel upgrade | Gas to electric or heat pump; electric tankless | Electrical code and the heater’s nameplate |
| Code items your old setup lacks | Inspection of the new install under current code | Local code; some are also manufacturer or warranty requirements |
| Hard access | Attic, crawlspace, tight closet, stairs | Code access rules; installer’s labor |
| Relocation | Moving the heater to a new spot | You, then code for everything that follows |
| Permit, haul-away, timing | Every job; emergencies | Local permit office; installer’s pricing |
Compiled from the sources in each section below. Codes vary by jurisdiction and edition; your local permit office has the final word on what applies.
Same-type replacement vs conversion: the biggest price difference
A same-type replacement keeps the same type and fuel in the same spot. The installer disconnects the old tank, sets the new one and reconnects the water, gas or power and the vent. Most of the connections already exist and only need checking.
A conversion changes one of those things, and each change reaches into another trade. Gas tank to gas tankless typically means a new vent, often a bigger gas line, a condensate drain and an outlet. Gas to heat pump means a 240-volt circuit (or a 120-volt model), a condensate drain, room for air, capping the gas line and sealing the old vent opening, all cost factors ENERGY STAR lists. Home Depot’s installers try to keep tankless units “near existing water and fuel sources” for the same reason. Price a conversion while the old heater still works; after a failure you usually end up with a same-type replacement.
Venting changes: the most variable line on a gas quote
Most older gas tanks are atmospheric: exhaust rises on its own through a metal vent or chimney, with no fan or electrical connection, which Rheem calls “often the simplest and most cost-effective option.” A same-type swap usually reuses the vent after the installer checks its size, slope and joints; Rheem lists those as mistakes that can let carbon monoxide back into the house.
Power vent and condensing models need a new vent and an outlet
A power-vent tank uses a blower to push exhaust sideways through a wall. A.O. Smith’s manual calls for PVC, CPVC or polypropylene pipe, a grounded 120-volt outlet within reach of a 6-foot cord (not a GFI outlet), and venting “separately from all other appliances.” Condensing tanks and tankless units also vent in plastic and make acidic condensate (pH 4.3–5.0, per A.O. Smith) that needs a drain; some codes require a neutralizer. This Old House puts power venting at $300–$600 plus $300–$500 of electrical work, and direct venting at $500–$1,000.
Orphaned chimneys and liners
In many older homes the furnace and the water heater share one chimney. Take one of them off it, by switching the water heater to a heat pump, electric or power-vent unit, or by replacing the furnace with a condensing model, and the remaining appliance is left alone in a flue sized for two. DOE calls this an orphaned appliance. Its exhaust may not vent properly through the oversized flue, and cooler modern exhaust condenses, which This Old House notes has damaged unlined masonry chimneys.
Gas appliance manuals spell out the fix. A.O. Smith’s instructions say that when a water heater is removed from a common vent, each remaining appliance must be tested, and the vent resized toward the minimum size in the National Fuel Gas Code (NFPA 54) tables. DOE’s water heater rule counts “addressing an orphaned furnace (by updating flue vent connectors, vent resizing, or chimney relining)” as a real installation cost. This Old House puts a new chimney liner at $500–$700. For how each vent type works, see water heater venting.
Gas line capacity: why tankless units often need bigger pipe
Gas pipe is sized for everything it feeds at once. The 2024 International Residential Code (section G2413.2) says “the total connected hourly load shall be used as the basis for pipe sizing,” and each appliance must get at least its minimum supply pressure. A tank burner is small; a whole-house tankless burner is not.
| Heater | Gas needed | 1/2-inch pipe carries | 3/4-inch pipe carries | 1-inch pipe carries |
|---|---|---|---|---|
| 40,000 BTU/h gas tank | 40 cubic feet per hour | 81 (enough) | 170 (enough) | 320 (enough) |
| 199,000 BTU/h gas tankless | 199 cubic feet per hour | 81 (too small) | 170 (too small) | 320 (enough) |
Capacity in cubic feet per hour for 40 feet of Schedule 40 steel pipe at a 0.5-inch water column pressure drop, from the NFPA 54-2021 table in Rinnai’s tankless manual, at 1,000 BTU per cubic foot. Illustration only: real sizing counts every gas appliance on the line and your actual pressure. On a higher-pressure system Rinnai’s second table shows 1/2-inch pipe carrying 214 at 40 feet.
That is why one installer may quote a new 1-inch line while another, finding higher supply pressure, reuses the existing pipe. This Old House puts a larger gas line for a tankless unit at $500–$1,000, and running gas to a house switching from electric at $1,500–$2,300. More in tankless water heaters.
Electrical: circuits, panel capacity and the 120-volt option
- Electric tank to electric tank or 240-volt heat pump: usually reuses the existing circuit. ENERGY STAR says a 240-volt heat pump model “typically utilizes a 30-amp circuit breaker and 10-gauge electrical wire, just like a standard electric storage water heater,” and some run on 25 or 20 amps.
- Gas to a 240-volt heat pump: needs a new 240-volt circuit to the heater, and ENERGY STAR says to confirm the panel “can support the additional load.” This Old House lists electrical work at $300–$800 in its tankless breakdown; a long run or a full panel costs more.
- Gas to a 120-volt heat pump: Rheem says plug-in models “may help avoid the cost of adding a new 240V circuit,” at the price of slower recovery. ENERGY STAR notes some need a dedicated outlet and others can share one, and that installers often size them up two steps from the gas tank (40 to 65 gallons).
- Electric tankless: the big one. Stiebel Eltron’s 24 kW Tempra 24 Plus needs two 50-amp double-pole breakers: 24,000 W ÷ 240 V = 100 amps, the whole rating of a 100-amp service. Its 36 kW model needs three. An electrician has to run a load calculation first, and a panel upgrade to 200 amps typically costs $1,300–$3,000 (This Old House).
- Power-vent and condensing gas units: need a 120-volt outlet near the heater; A.O. Smith specifies a grounded outlet, dedicated preferred.
You can check part of this yourself: look for a 30-amp double breaker marked for the water heater, and note whether your main breaker says 100, 150 or 200. A full panel or a 100-amp main means getting an electrician’s opinion before you pick a model. Weighing a fuel switch? See switching from gas to electric or heat pump.
Code upgrades your old installation may be missing
Codes have tightened since many existing heaters went in. A replacement usually needs a permit, and the inspector checks the new install against current local code, so items the old one lacked can appear on the quote. The diagram shows where each sits on a typical gas tank.
| Item | What it does | Usually required when | Published add-on cost |
|---|---|---|---|
| Expansion tank | Absorbs the pressure rise as water heats | A check valve, backflow preventer or pressure regulator “closes” the system (2024 IRC P2903.4.2) | $40–$150 |
| Seismic straps | Keep the tank from toppling and breaking its gas line | All residential heaters in California (Health and Safety Code 19211); higher seismic zones under the IRC (P2801.7). Upper and lower thirds, the lower strap 4 inches above the controls (Las Vegas, Ventura) | $100–$300 |
| Drain pan | Catches leaks | Where a leak would cause damage, such as attics (IRC P2801.5); a replacement needn’t add a pan drain if none existed (P2801.5.1) | $50–$200 for drainage |
| Relief valve discharge pipe | Carries scalding water from the T&P valve to a safe place | Always. Full size, downhill, no valves or threaded end, ending within 6 inches of the floor, a pan, a drain or outdoors (ICC); some cities require outdoors | $20–$200 for valve work |
| Sediment trap (drip leg) | Catches debris before it reaches the gas valve | Gas heaters without a built-in trap (A.O. Smith manual, NFPA 54; Las Vegas, Hayward) | Small; usually in materials |
| Shutoff valves | Let the heater be isolated | Cold-water shutoff at the heater (IRC P2903.10.2); gas shutoff within 6 feet (Las Vegas, Hayward) | $200–$600 with other water-line changes |
| Bonding | Keeps metal piping at ground potential | Existing bonding “must be maintained” on a replacement (Las Vegas); gas piping bonding (Hayward) | Small; ask |
| Vacuum relief valve | Lets air in so a draining tank can’t be sucked inward | Specific setups, such as a tank above the fixtures it serves (California Plumbing Code 608.7); A.O. Smith says to install one “per local codes” | Small; ask |
| Garage elevation or protection | Keeps flame away from gasoline vapors, and cars away from the heater | Ignition source 18 inches above the floor unless flammable-vapor ignition resistant (IRC P2801.6); barriers in a car’s path | Platform or bollard; ask |
Costs: This Old House’s published ranges (updated June 2026) where it lists the item; others are typically folded into materials. Code sections: 2024 International Residential Code, the ICC’s CodeNotes on relief-valve discharge, and the published replacement checklists of Las Vegas, Ventura and Hayward (which use the Uniform/California Plumbing Code). Your jurisdiction may differ.
Some items are also manufacturer requirements, which matters for your warranty: A.O. Smith says thermal expansion tanks “must be installed on all closed water systems” and that thermal-expansion damage isn’t covered. If your water meter or main has a check valve or pressure-reducing valve, an expansion tank is not an upsell. More in expansion tanks and water heater code requirements.
Location and access: attics, crawlspaces, closets and garages
Basements are usually the easiest place to work. Everywhere else adds labor, safety measures or both.
- Attic: This Old House puts attic installs at $200–$1,000 extra. Carrying the new tank up and the old one down is slow, and a leak does the most damage there, so a drain pan with a drain line is expected. Ventura’s checklist also has inspectors verify the attic access opening, passageway and work platform, and a 120-volt outlet and a light switched at the attic entrance.
- Crawlspace: the same problems in a smaller space: a tight opening, a long crawl, and a full-size tank to move in and out.
- Closet: under the IRC (M2005.2), a fuel-fired heater can’t go in a room used as a storage closet, and one in a bedroom or bathroom needs a sealed enclosure unless it is direct vent. Hayward requires two 100-square-inch combustion-air openings in a gas heater’s closet; This Old House lists $200–$800 for closet ventilation. Heat pump models need air too: ENERGY STAR says most 240-volt units want about 700 cubic feet, or a louvered closet door.
- Garage: gas units need the 18-inch rule or a flammable-vapor-resistant design (above), protection from cars, and in cold climates This Old House lists $100–$300 for freeze protection.
- Stairs and tight routes: a narrow stair or a heater boxed in by later remodeling adds time. Photos help the installer price it; see the photo checklist.
Relocation: moving the heater rebuilds everything around it
Moving a heater means new water lines, a new gas line or circuit, a new vent route and a new relief-valve discharge, plus every location rule for the new spot. This Old House lists $200–$600 for relocating water lines alone. Vent terminations come with clearances too; on one This Old House job the vent had to sit at least 3 feet from a gas meter, 2 feet from a fence or wall and 12 inches above grade. Hayward and Las Vegas both require a permit to relocate a water heater.
It can still pay off: freeing a closet, getting a tank out of an attic, or giving a heat pump the air it needs. Ask for the move as its own line. See where a water heater can go.
Permits, haul-away and after-hours work
- Permit and inspection: usually small. La Mirada, California charges about $76 for a water heater permit; Portland, Oregon lists $63; This Old House says $50–$200. The inspection also checks the gas, vent and relief-valve work. See permits and inspections.
- Haul-away: This Old House lists $100–$300 for disconnection and disposal “according to local regulations.” Home Depot includes removal in its ranges. Make sure your quote says which.
- After-hours and emergency: This Old House lists $200–$500 extra. Not everyone charges it: Home Depot offers same-day tank installation at no extra charge in most areas when you call before noon on a weekday.
Will my job need this? A quick self-check
You can answer most of these from a walk around the heater. Each “yes” is a line item to expect, or to ask about if a quote leaves it out.
Look for these before you call
- Are you changing type or fuel (tank to tankless, gas to heat pump or electric)? Expect venting, gas or electrical work.
- Does the heater’s vent pipe join the furnace’s vent before the chimney? Changing either appliance may need vent resizing or a liner.
- Is there a small tank on the cold-water pipe above the heater? If not, check the water meter or main for a check valve or pressure regulator: that means an expansion tank.
- Do you live in California or another earthquake-prone area, and are there no metal straps around the tank?
- Is the heater in an attic, on an upper floor or over a finished room, with no pan under it?
- Does the relief-valve pipe stop short, run uphill, shrink in size or end in a threaded fitting?
- On a gas tank, is there no capped vertical pipe (drip leg) below where the gas line connects?
- Is the heater in a garage with the burner less than 18 inches off the floor, or where a car could hit it?
- For a heat pump or electric tankless: is there a 240-volt circuit at the heater, and what does your main breaker say?
Bring the answers, and photos, to every installer, then compare how each one handles them with our guide to comparing quotes line by line.
Common questions
Why is my water heater installation quote so much higher than the price of the heater?
Labor, materials, permit, haul-away and any work the house needs come on top of the heater. ENERGY STAR’s rule of thumb for heat pump models is that installation costs about as much as the unit. Venting, gas, electrical and code items explain most of the rest; ask for them as separate lines.
Do I need an expansion tank when I replace my water heater?
If your water system is “closed” by a check valve, backflow preventer or pressure-reducing valve, most codes require thermal expansion control, usually an expansion tank (2024 IRC P2903.4.2). A.O. Smith also requires one on closed systems for warranty purposes. This Old House puts the add-on at $40–$150.
Why does switching to a tankless water heater cost so much more?
A whole-house gas tankless unit burns up to about 199,000 BTU/h against roughly 40,000 for a typical tank, so it often needs a bigger gas line, plus a new vent, a condensate drain and an outlet. Home Depot says tank-to-tankless changes will likely cost more than its $2,400–$5,400 range.
Will I need a new electrical panel for a heat pump water heater?
Often not. Replacing an electric tank usually reuses the existing 30-amp, 240-volt circuit, and 120-volt plug-in models can avoid a new circuit when replacing gas. A panel upgrade is more likely for whole-house electric tankless units, which can draw 100 amps or more. An electrician’s load calculation settles it.
What is an orphaned water heater?
It is a gas water heater left alone in a chimney it used to share with a furnace, usually after the furnace is replaced with a condensing model that vents through plastic pipe. The chimney is now too big for the small heater’s exhaust, so the vent may need resizing or a liner. The same thing happens to a furnace when the water heater leaves the chimney.
Do I have to bring my old installation up to code when I replace the water heater?
A permitted replacement is inspected against your jurisdiction’s current code, so items like straps, an expansion tank or a proper relief-valve discharge are commonly required. Some codes grandfather specific items; the IRC, for example, doesn’t require adding a pan drain if none existed. Your local permit office decides.
Does moving my water heater to another spot cost much more?
Usually, because the water lines, gas line or circuit, vent and relief-valve discharge all have to be rerouted. This Old House lists $200–$600 just for relocating water lines; venting and gas or electrical work come on top.
Sources
Sources checked October 4, 2026. Prices, codes and rebates change. Check current details with your installer and local permit office.
- Cost to Replace a Water Heater (national ranges and what they include) ↗ · Home Depot
- How Much Does Water Heater Installation Cost? (updated June 17, 2026) ↗ · This Old House
- How Much Does It Cost to Upgrade an Electrical Panel? (updated March 31, 2026) ↗ · This Old House
- What Goes into the Cost of Installing a Heat Pump Water Heater? ↗ · ENERGY STAR
- Best Practices: Installing Heat Pump Water Heaters (installer guide, 2024) ↗ · ENERGY STAR
- 120V vs. 240V heat pump water heaters ↗ · Rheem
- Gas water heater types explained: atmospheric, power vent, direct vent ↗ · Rheem
- The top installation mistakes plumbers see with water heaters ↗ · Rheem
- Residential power vented gas water heaters: installation and use and care guide (2023) ↗ · A.O. Smith, hosted by Lowe’s
- Residential condensing gas water heaters: installation and operating manual ↗ · A.O. Smith, hosted by Lowe’s
- XP Plus water heater installation and operation manual (removing a heater from a common vent) ↗ · A.O. Smith
- Tankless water heater installation and operation manual (gas pipe sizing tables) ↗ · Rinnai, hosted by Lowe’s
- Tempra Trend / Tempra Plus submittal sheet ↗ · Stiebel Eltron
- Energy conservation standards for consumer water heaters, final rule (installation costs, orphaned furnaces) ↗ · U.S. Department of Energy, Federal Register, May 6, 2024
- Final interpretive rule on furnaces and water heaters (definition of an orphaned water heater) ↗ · U.S. Department of Energy, Federal Register, December 29, 2021
- CodeNotes: Water heater safety in the I-Codes (relief valve discharge, 2021 IPC 504.6 / IRC P2804.6.1) ↗ · International Code Council
- 2024 IRC Chapter 28, Water Heaters (P2801.5–P2801.7) ↗ · International Code Council
- 2024 IRC Chapter 29, Water Supply and Distribution (P2903.4.2, P2903.10.2) ↗ · International Code Council
- 2024 IRC Chapter 24, Fuel Gas (G2413 pipe sizing) ↗ · International Code Council
- 2024 IRC Chapter 20, Boilers and Water Heaters (M2005.2 prohibited locations) ↗ · International Code Council
- California Health and Safety Code §19211 (water heater strapping) ↗ · California Legislative Information
- California Plumbing Code 608.7, vacuum relief valves (2025 edition) ↗ · GoCodeBook
- Residential water heater installation guideline ↗ · City of Las Vegas Building & Safety
- Inspection checklist: water heater replacement ↗ · City of Ventura, California
- Residential water heater replacement checklist (revised 2021) ↗ · City of Hayward, California
- LFN36-M1 vacuum relief valve specification sheet ↗ · Watts, hosted by G.T. Sanders
- 2026–27 City of La Mirada plumbing code fees ↗ · Los Angeles County Public Works
- Plumbing permit fee schedule, effective July 10, 2026 ↗ · City of Portland, Portland Permitting & Development