Most solar hot water quotes are “average household” fiction.
They’re built on tidy assumptions: a standard number of showers, a generic inlet water temperature, a perfectly sunny roof, and a family that behaves like a spreadsheet. Real homes don’t. If you want a quote that reflects your actual usage, your Saturday laundry pile-ups, your winter shower marathons, your teenagers’ mysterious ability to empty a tank, you have to bring better inputs and demand better outputs.
And yes: installers who are truly good at this will welcome that.
Hot take: if the quote doesn’t model your demand, it’s not a quote, it’s a guess.
Here’s the thing. Solar hot water is brutally sensitive to timing and temperature. A household that uses the same total hot water per day can need very different system sizing depending on when they draw it, what the incoming cold water temperature is, and how aggressive their backup heater is set.
So if someone gives you a price without asking for consumption patterns, seasonal variation, and site specifics, you’re not seeing engineering, you’re seeing sales. Before you get a solar hot water quote, make sure the provider is actually modelling your demand.
What “real-use quoting” looks like (not the brochure version)
A proper quote doesn’t just hand you a system size and a dollar figure. It shows:
– Estimated monthly solar contribution (kWh or MJ displaced, not just “% savings”)
– Assumptions: inlet water temps by season, desired setpoint, occupancy, load profile
– Collector output modeled for your orientation/tilt/shading, not lab-rated efficiency
– Storage tank sizing tied to first-hour demand and recovery rate
– Backup energy assumptions (gas, electric resistance, heat pump) and tariff timing
– Itemized costs: equipment, labor, permits, roof work, plumbing upgrades, controls
If it doesn’t separate those, you can’t compare proposals. You’re just comparing storytelling styles.
One-line reality check: a “cheap” quote that excludes tempering valves, recirc fixes, or roof repairs isn’t cheap, it’s incomplete.
Track your current hot water use (without turning your life into a science project)
Now, this won’t apply to everyone, but… most households can get 80% of the needed accuracy in two weeks of decent tracking, plus bills.
If you have a hot water meter, great. If you don’t, you can still get usable numbers.
The simplest workable approach
Track:
– Shower count + approximate minutes
– Laundry cycles (hot/warm/cold)
– Dishwasher runs
– Any big one-offs (guests, filling a tub, back-to-back showers)
Log it by day. A spreadsheet is fine. A notes app is fine. Consistency beats perfection.
In my experience, the biggest “aha” comes from noticing clumping: people don’t use hot water smoothly over a day, they spike it.
Peaks matter more than averages (and that’s where quotes go wrong)
Averaging daily hot water use is comforting…and misleading.
A system can meet your average day and still fail you on the mornings that matter. Installers should be asking about:
– The busiest hour of hot water use (often 6, 9am or 7, 10pm)
– Back-to-back showers
– Weekend vs weekday behavior
– Whether you run laundry/dishwasher in the evening
If a quote doesn’t talk about peak draw, it’s probably sizing off a rule-of-thumb number like “X gallons per person per day,” which is how people end up with systems that underperform, or with oversized tanks that bleed heat all night.
Seasonal trends: the quiet budget killer
Winter changes everything. Incoming mains water is colder, heat losses rise, showers run longer, and collectors produce less. That combination is why year-round performance claims can be… optimistic.
If you want to be disciplined, track a full year. If you can’t, at least bring two things to the table:
1) Your winter utility bills
2) Your local average cold-water inlet temps or at least a proxy (monthly air temps)
A specific data point that installers should respect: according to the U.S. Energy Information Administration, water heating accounts for about 12% of residential energy use on average in the U.S. (EIA, “Use of energy explained: Energy use in homes”). Average isn’t your home, but it frames why small modeling errors can distort payback.
Sizing the system to real needs (the technical bit, but not too painful)
You’re basically matching three things:
Load (your demand) → Collector output (your roof + climate) → Storage + backup strategy (your comfort tolerance)
A competent quote will translate your usage into:
– Daily hot water volume (gallons or liters)
– Desired delivery temperature (often ~120°F / 49°C in many homes, but it varies)
– Seasonal inlet temps
– Expected solar fraction by month
– Backup run time or energy use by month
Look, oversized systems aren’t “future proof.” They’re often just expensive. Bigger tanks have higher standby losses unless insulation is exceptional, and too much collector area can cause overheating issues in some climates without proper controls.
I’ve seen homeowners pay for collector capacity they can’t practically use because the real constraint was storage and draw timing, not “more sun capture.”
Tech choices that quietly change your daily routine
People talk about “solar hot water” like it’s one thing. It isn’t. The technology you pick changes how you’ll operate the house.
Solar thermal (collectors + tank)
Efficient at turning sunlight into heat. Can be fantastic where installed well. Also more plumbing complexity. Maintenance matters.
PV + heat pump water heater (HPWH)
This is the option I’ve grown more bullish on over time (especially where thermal installers are scarce). It’s flexible, simpler on the roof, and can ride on cheap daytime solar electricity. But the performance depends on ambient conditions and installation location.
PV + resistance element
Simple. Usually lower efficiency than HPWH. Sometimes still reasonable if PV is abundant and tariffs are friendly.
One opinionated note: if the quote compares thermal to PV without aligning assumptions (tariffs, backup fuel cost escalation, maintenance), it’s not a comparison, it’s marketing.
Turn your tracking into a quote request installers can’t wiggle out of
Send a one-page “brief.” Short. Blunt. Specific.
Include:
– Location (city + rough elevation if relevant)
– Household size + typical schedule (work-from-home matters)
– Estimated daily hot water use and peak hour events
– Roof photos (wide + close-up of penetrations and shading)
– Roof orientation and pitch (even approximate)
– Current water heater type, age, fuel, and capacity
– Any known plumbing quirks: recirculation loop, long pipe runs, low pressure
– Your comfort preferences (you want endless hot water? or “good enough”?)
Then say: “Provide an itemized quote and a monthly performance estimate based on these inputs.”
The good firms won’t flinch.
Questions that force parity across bids (because otherwise you’re comparing apples to sketchy oranges)
Ask each installer to answer these in writing:
1) What model did you use for solar production, and what weather dataset?
2) What inlet water temperatures are assumed by month?
3) What hot water setpoint is used, and are mixing/tempering valves included?
4) What solar fraction do you predict by month, and what backup energy remains?
5) What exactly is included in plumbing work (valves, expansion tank, isolation, pipe insulation)?
6) What’s the monitoring plan post-install, and who reviews performance?
7) What’s excluded (roof repairs, electrical upgrades, permits, crane/lift costs)?
If they get irritated by this, that tells you something.
A practical quote checklist (small list, because it helps)
You want each proposal to clearly show:
– Collector area or PV capacity, plus expected output under your conditions
– Tank size + recovery performance (not just “big enough”)
– Installed cost breakdown (equipment vs labor vs permits vs extras)
– Maintenance requirements + expected costs over time
– Warranties for collector/PV, tank, pumps/controllers, and labor
– Assumptions page (if there’s no assumptions page, run)
Incentives and ROI: don’t let the math get “creative”
Some quotes magically produce paybacks by stacking best-case assumptions: high fuel inflation, perfect sun, no maintenance, and incentives you may not qualify for.
Push for ROI under at least two cases:
– Conservative (cloudier year, normal maintenance, modest energy inflation)
– Expected (typical weather, normal usage, realistic system aging)
And insist incentives are shown separately: gross cost, incentive value, net cost. If the installer can’t tell you exactly which program rules they’re relying on, you’ll be the one holding the bag when paperwork gets rejected.
Final thought (not a wrap-up, just the truth)
A solar hot water system can be a great upgrade. But the quote has to be anchored to your behavior, your roof, and your winters. Anything less is a shiny estimate with a confidence problem.