A tankless water heater is a significant purchase, and the quality of the installation matters as much as the quality of the unit. Before you sign a quote, it pays to ask the right questions of yourself, the retailer and the installer. This checklist is organized by topic so you can work through it in order, take notes and compare bids on equal terms. It applies whichever manufacturer you are considering; we do not recommend or endorse a particular brand.
General information only. Local codes, utility rules and product details vary. Use licensed professionals for gas, venting and electrical work.
Part 1: Questions for Yourself
1. How much hot water do we really need?
Think about your busiest morning: how many showers, how many appliances? Count fixtures that run at once. This number drives sizing; see our sizing guide.
2. What is our coldest incoming water temperature?
Winter groundwater is much colder than summer. Size for the coldest period.
3. What fuel do we have?
Natural gas, propane or electricity? Switching fuel adds cost. Our gas vs electric installation guide lays out the differences.
4. How long will we stay in the house?
A longer horizon makes it easier to justify a higher upfront cost. Use the payback method in our tank vs tankless comparison.
5. What is our budget, including installation?
Plan for the unit plus venting, gas or electrical upgrades, permits and labor, not just the sticker price.
6. Do we have hard water?
If yes, plan for descaling or a softener. See how to flush a tankless water heater.
Part 2: Questions for the Installer
Sizing and selection
- Can you show me the sizing calculation, including flow rate and temperature rise?
- What incoming water temperature did you assume?
- Why this model and capacity rather than larger or smaller?
- Do you recommend one unit or two?
Gas and electrical
- Will my existing gas line support the new unit along with my other appliances? Will you do a gas load calculation?
- If electric, does my panel have capacity? What breakers and wire gauge are required?
- Is a service upgrade needed?
- What happens in a power outage? Do you recommend backup power?
Venting and location
- What venting type and routing will you use?
- Is the vent length and number of elbows within the limits?
- Where will the termination be, and does it meet clearance rules?
- How will combustion air be supplied?
- Where will the condensate drain? Do I need a neutralizer or pump?
Plumbing
- Will you install isolation valves for easy flushing?
- Do I need a pressure relief valve, expansion tank or pressure regulator?
- Will a recirculation pump or buffer tank improve my hot water wait times? Is it compatible with the unit?
- How will the unit handle low flows at my fixtures?
Safety and codes
- Will you pull the permit and arrange inspection?
- Are you licensed and insured? Can you provide proof?
- Will carbon monoxide detectors be checked or added?
Part 3: Questions About the Product
Efficiency and operation
- What is the efficiency rating, and is it for the exact model quoted?
- Is it condensing or non-condensing?
- What is the minimum activation flow?
- What is the maximum flow at my temperature rise?
- What temperature range can I set? Is there a controller?
- How loud is it in operation? Where will it be mounted?
Features
- Does it include or support scale detection, diagnostics or app connectivity? Are those features important to you?
- Are there freeze protection features for outdoor installations?
Compatibility
- Is it approved for my fuel type and altitude?.
- Can it be paired with a recirculation system or solar preheat?
Part 4: Warranty, Service and Maintenance
- What does the warranty cover (heat exchanger, parts, labor) and for how long?
- Does the warranty require professional installation or documented maintenance?
- What does the installer’s labor warranty include?
- How often should it be serviced, and who will do it?
- Are replacement parts readily available?
- What is the process if something fails, and what is the typical response time?
Warranty terms differ by manufacturer, model and region. Read the actual documents rather than relying on summaries.
Part 5: Quote Comparison
When you receive quotes, put them side by side:
| Item | Quote A | Quote B | Quote C |
|---|---|---|---|
| Unit model and capacity | |||
| Sizing calculation provided? | |||
| Venting type and materials | |||
| Gas or electrical upgrades | |||
| Permits and inspection | |||
| Isolation valves | |||
| Condensate handling | |||
| Haul-away of old unit | |||
| Labor warranty | |||
| Total price |
Be wary of quotes that are much lower than others without explanation. They may omit permits, venting or upgrades.
Part 6: Money Matters
- Are there utility or government rebates, tax credits or financing options? Check official sources.
- What deposits or payment terms are required?
- What is the cancellation policy?
- Are there extra charges for changes discovered during the job?
Red Flags in Quotes
- No site visit or load calculation
- No mention of permits
- Vague descriptions of materials
- Pressure to sign immediately
- Claims of guaranteed savings
- Dismissal of venting or gas line concerns
After You Buy
- Keep manuals, receipts and warranty documents together.
- Register the product if required.
- Note the installation date and set a maintenance reminder.
- Test hot water at all fixtures after installation.
- Learn how to read error codes and where to find help.
- Check that carbon monoxide detectors are working.
For common questions on lifespan, noise and venting, see our tankless FAQ.
Tankless Water Heater FAQ: Lifespan, Noise and Venting
Frequently Asked Questions
How many quotes should I get?
Three is a common recommendation. Compare itemized quotes, not just totals.
Should I buy the unit myself and hire an installer?
Some installers will not warrant work on customer-supplied units, and warranties may require professional installation. Ask first.
What if my home needs upgrades?
Ask for an itemized estimate of those costs. They can change the economics, so factor them into your decision.
Is online buying safe?
It can be, provided the seller is authorized, the product is covered by warranty and an installer will work with it. Verify before purchase.
Conclusion
Buying a tankless water heater goes best when you ask detailed questions, insist on itemized quotes and use licensed professionals. Know your demand, your infrastructure and your budget, and make sure warranty and maintenance are clear. Use this checklist to compare options on equal terms and avoid surprises.
