The honest 2026 answer for a Southeast Michigan gunite pool: a 400K BTU natural gas heater is the right answer for about 80% of homeowners we work with. Heat pumps make sense for a specific subset of customers with the right electrical service and the right swim habits. Solar still has a role, but mostly as a supplement — not a primary heat source — in our climate.
Here is the full comparison — what each one costs to install, what it costs to run, how fast it heats, how far it extends your season, and which one we install most often.
The Michigan climate context
Pool heaters get evaluated in two dimensions: speed (BTUs delivered per hour — how fast can it raise water temp) and efficiency (cost per BTU delivered). The right answer in San Diego is not the right answer in Bloomfield Hills, because Michigan asks a heater to do three different jobs:
- Spring startup — take a 50°F pool to 82°F in 1–2 days. Brutal on slow heaters.
- Holding mid-summer — keep an 82°F pool against cool nights and occasional cold fronts.
- Shoulder season — September and October, when air drops to the 50s overnight but the pool is still 70 in the day.
Different heaters handle those jobs very differently. That’s the whole game.
Option 1: Natural gas heater (Pentair MasterTemp / Raypak / Hayward H-Series)
What it is: A box on your equipment pad that burns natural gas to heat water directly. Industry-standard residential size for gunite pools is 400,000 BTU/hr. Connected to your home’s natural gas line.
| Metric | Natural gas heater |
|---|---|
| Install cost (heater + plumbing + gas line) | $4,500–$8,500 |
| Run cost (heated month, MI rates) | ~$200–$450 |
| Heat-up rate (20,000 gal pool) | ~1.5°F per hour |
| Time from 50°F to 82°F | ~22–28 hours |
| Season extension | April–October realistic |
| Service life (well-maintained) | 10–15 years |
The case for: Fast. Works on any cool day. Reasonable purchase price. Runs reliably for a decade-plus with annual servicing. Pays you back in actual usage — people swim in pools they can warm up the morning of, not pools they have to plan two days ahead for.
The case against: Natural gas costs money to burn. If you heat to 88°F all season and run the pool May through September, you will spend $1,500–$2,500 a year on gas. Propane equivalents (for homes without natural gas service) run 30–50% higher.
Who should buy it: Almost everyone. If you have natural gas at the house, this is the default for a reason.
Option 2: Heat pump (Pentair UltraTemp / Hayward HeatPro / Jandy AE-Ti)
What it is: An electric appliance that pulls heat from outside air and moves it into your pool water. Essentially a one-way air conditioner. Runs on electricity, no gas line needed.
| Metric | Heat pump |
|---|---|
| Install cost (heater + electrical) | $5,500–$10,000 |
| Run cost (heated month, MI rates) | ~$120–$300 |
| Heat-up rate (20,000 gal pool) | ~0.5°F per hour |
| Time from 50°F to 82°F | ~60–75 hours (~3 days) |
| Season extension | Mid-May through September |
| Service life | 8–12 years |
The case for: Roughly 30–50% cheaper per heated month than gas in mid-summer. Quieter than gas heaters. No combustion = no risk of gas-line issues. Works well if you swim consistently from June through August at a steady set point.
The case against: Slow. It cannot recover from cold nights fast enough to be practical for spring or fall in Michigan. Once outside air drops below ~55°F at night, efficiency drops sharply. Requires a 50-amp circuit and a properly sized electrical panel — about 30% of older Michigan homes need a panel upgrade to make the install work.
Who should buy it: Homeowners who plan a steady summer-only swim schedule, have modern electrical service, and want lower monthly cost more than they want fast heat-up. We also install them sometimes as a second heater paired with gas — gas does the spring heat-up, heat pump holds temperature efficiently in July and August.
Option 3: Solar pool heating
What it is: Roof-mounted (or rack-mounted) plastic collector panels. Pool water circulates through the panels on sunny days, picking up heat from the sun, returning warmer to the pool. Zero fuel cost to operate beyond the pump electricity.
| Metric | Solar |
|---|---|
| Install cost (panels + plumbing + controller) | $3,500–$8,000 |
| Run cost (per month) | ~$0 (pump electricity only) |
| Heat-up rate | Highly variable — sun dependent |
| Realistic season extension | 2–4 weeks of “shoulder” each side |
| Service life | 10–20 years (panels) |
The case for: Effectively free heat in July and August. Zero operating cost. Long panel life. Quiet. No combustion.
The case against: Michigan. We get roughly 75 fully sunny days per year. A solar-only pool will not be reliably warm in May or September. Roof aesthetics — solar panels are visible. Performance during the cold week you actually want a hot pool is exactly when solar is at its weakest.
Who should buy it: Mostly customers who want to supplement a gas heater — let the sun handle July, let gas handle May, September, and any cold week in between. Pure-solar is a tough sell in our latitude.
Solar covers and liquid solar — the cheap retention play
Different category, often confused with solar heating. A solar cover (or solar blanket) is a sheet of bubble-wrap-like material that floats on the pool surface when not in use. It does not heat the water meaningfully — what it does is dramatically reduce evaporative heat loss overnight. Cost: $100–$400 plus a reel to wind it up.
Liquid solar blankets are a single-molecule-thick chemical that does the same thing. Less effective than the physical cover, but works on pools where reeling a cover is impractical.
Either one cuts heater run time by 30–50%. They are the single highest-ROI accessory we install. If you are spending money on a heater, also buy the cover.
What we actually install — and our recommendation by use case
| Your situation | Our recommendation |
|---|---|
| Standard home with natural gas, family wants flexibility | 400K BTU gas heater + solar cover |
| Steady summer-only swimmer, modern panel | Heat pump + solar cover |
| Heavy use, season-long, budget supports it | Gas heater + heat pump pairing |
| Propane only (no natural gas at home) | Heat pump (or upsized gas + budget for propane) |
| South-facing roof, willing to supplement | Gas heater + solar panels for July/August |
| Spa user, year-round nights | Gas heater — non-negotiable for spa recovery time |
What to do next
If you are mid-build with us, the heater conversation is part of the equipment-pad walk we do during design. If your pool is older and you are considering a heater upgrade, message or call us — we will tell you honestly whether your existing pad and gas service support the heater you have in mind, or whether a heat pump is the better fit given your home’s situation. More on heating and add-ons here.
Frequently asked questions
What size gas heater do I need for a Michigan gunite pool?
For a standard 18×36 family pool (~20,000 gallons), a 400,000 BTU gas heater is the residential standard. Larger pools or pools paired with spas often step up to a 500K BTU unit. We size the heater during the equipment-pad design conversation.
Will a heat pump work in May in Michigan?
Slowly. Heat pumps lose efficiency rapidly once outside air drops below 55F, which happens overnight on most early-May days. They can hold a warm pool but struggle to recover from cold nights in the shoulder seasons. We rarely recommend heat-pump-only in Michigan.
Is solar pool heating practical in Michigan?
As a supplement, yes. As a sole heat source, no. Solar pairs well with a gas heater for July and August efficiency. Solar-only installations cannot reliably keep a Michigan pool warm in May, September, or any cold front.
What does it cost to run a gas pool heater for a season?
For a typical 20,000-gallon pool heated to 82F from mid-May through mid-September with a solar cover at night, plan on $1,200-$2,200 in natural gas for the season. Without a solar cover, that number roughly doubles.
Can I add a heater to an existing pool?
Almost always yes. We add heaters to existing gunite, fiberglass, and vinyl pools regularly. The job involves running gas to the equipment pad (or electrical for a heat pump), plumbing the heater into the existing equipment run, and re-commissioning the pad. Most heater retrofits are a one-day install.
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