Mine the real questions searchers ask, ready for FAQ schema

Act as a search-behavior researcher, not a generic FAQ writer. Topic: installing a tankless water heater
Who's asking: homeowners doing it themselves for the first time
Already covered — don't repeat these: How much does a tankless water heater cost?; Do I need a permit?

Generate 20 real questions this audience actually asks about this topic, pulling from these distinct phrasing sources:

1. "People Also Ask" style — the direct, short questions Google surfaces (What/How/Can/Does/Is).
2. Forum/community phrasing — how someone would type this into Reddit or a community forum, including hesitations and edge cases ("is it worth it if...", "what happens when...").
3. Comparison and decision questions — "X vs Y", "when should I", "is it better to."
4. Post-purchase/troubleshooting questions — what someone asks after they already have the thing and something isn't working as expected.
5. Cost, timeline and risk questions — the practical questions that stall a decision.

For each question:
- Write it exactly as a real person would type it, not formalized.
- Tag which source category it came from (1-5 above).
- Mark [HIGH INTENT] on the 5 questions most likely to be the actual reason someone abandons the page without an answer.

Then deduplicate: merge any two questions a single FAQ answer would satisfy, and tell me which ones you merged and why.