Pentair MasterTemp 400 review
The biggest common gas class, and by its listings' account the quiet one. What is published, the number that is not, and who it is for.
Quick picks
Both fuel versions of the MasterTemp, plus the heater whose listings publish the number Pentair's do not. Ranked on what is published.
| # | Product | Best for | Price |
|---|---|---|---|
| 1 |  The one being reviewed Pentair MasterTemp 400 Natural Gas Pool Heater 400,000 BTU/hr, low NOx, about five hours for 20,000 gallons. The natural gas version. | A full-size pool heated on demand, when you want the largest gas class | |
| 2 |  The same heater, no gas line needed Pentair MasterTemp 400 Propane Pool Heater Propane burner. About $35.66 per million BTU against $28.36 on natural gas. | A full-size pool heated on demand, where there is no natural gas | |
| 3 |  The alternative that states its efficiency Raypak Digital Natural Gas Pool Heater 336,000 BTU/hr, 82% printed in the listings. About an hour slower on the same job. | Heating fast and occasionally, rather than holding a temperature |
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
What Pentair's listings actually say
Reading the current listings on 12 September 2026, the MasterTemp 400 is a 400,000 BTU/hr input gas heater, sold in natural gas and in liquid propane versions, certified for low-NOx emissions, and described as having best-in-class energy efficiency and as noticeably quieter than older gas designs. The propane listing carries the same figures with a different burner.
What the listings do not say is a percentage. “Best in class” is a claim about efficiency without a number attached to it, and on a site whose whole method is dividing published figures by each other, that is the finding worth leading with. We run this heater at the 82% we assume for every gas heater, and we would revise it the moment Pentair published a figure we could cite.
What the class buys you
400,000 BTU/hr is the largest residential gas class in common use, and the reason to want it is time:
| 20,000 x 8.33 x 10°F | = 1,666,000 BTU |
| 400,000 BTU/hr x 82% (assumed) | = 328,000 BTU/hr delivered |
| 1,666,000 ÷ 328,000 | = about 5 hours |
| Natural gas: 1.666 x $28.36 | = $47.24 |
| Propane: 1.666 x $35.66 | = $59.41 |
Ideal figures that ignore heat lost during the heat-up. Note that the fuel cost for the job is the same as a 336,000 BTU/hr heater's — a bigger burner uses the fuel faster, not more of it. US average residential prices, EIA, June 2026.
About five hours against about six for the Raypak 336. That hour is real and it is the entire performance difference between the two on published figures. What the extra input also buys you is a larger gas demand, and that is the part to read next.
The gas line, before anything else
The quiet claim
The listings describe the MasterTemp as quieter than the older designs, and it is the one claim here that is genuinely about the product rather than the class. We cannot measure it and no listing gives a decibel figure, so we record it as a description rather than a specification. If the heater sits near a patio or a bedroom window, it is worth asking a dealer for a number or hearing one running.
Low NOx
The unit is certified for low nitrogen-oxide emissions, which is not a performance feature but a permission one: several air-quality districts require it, and a heater without it cannot legally be installed there. All three brands in this class carry it on their current units; it is worth confirming on any older or discounted stock.
Natural gas or propane
The same heater with a different burner, sold under a different part number. The performance is identical; the fuel is not. At US average residential prices propane costs about $35.66 per million BTU delivered against $28.36 on natural gas — a quarter again more — and it comes from a tank on a delivery contract rather than a line. If you have natural gas, buy that version. If not, the propane MasterTemp is the fast option and the heat-pump comparison gets harder for it to win.
Who it is for
The on-demand household with a gas supply that can feed it: a pool used unpredictably, warmed for a weekend or a cold snap, where hours matter and running cost applies to a handful of them a month. In a cold shoulder season, where a heat pump fades, the case gets stronger.
It is the wrong buy for holding a temperature all season, where a heat pump at about $10.75 per million BTU beats every gas heater on running cost by a wide margin, and that comparison should come before this page.
What we could not assess
The efficiency it actually delivers, since no percentage is published to check. Heat exchanger material and life — the listings we read do not state the exchanger material, which on a gas heater is the component your water chemistry attacks first. The noise figure behind the quiet claim. And whether your gas supply can feed it, which is a question for a fitter.
The three-brand comparison sets it beside the Raypak and the Hayward on everything each publishes.
Every pick, in detail
What each one publishes, what is good and bad about it, and — the section this category usually omits — what we could not judge without owning one.
Pentair MasterTemp 400 Natural Gas Pool Heater
The third name in every gas-heater comparison, and the one the listings describe as the quiet one. It is a 400,000 BTU/hr input heater, low-NOx certified, which puts it in the same class as the biggest Raypak — and therefore in the same speed bracket: hours rather than a day. Pentair does not state a thermal efficiency percentage in the listings we read, so we run it at the 82% we assume for gas generally.
Best for A full-size pool heated on demand, when you want the largest gas class
| Rated input | 400,000 BTU/hrGas convention: fuel burned per hour, not heat delivered. Delivered heat is this figure times the thermal efficiency. | Retail listing |
|---|---|---|
| Emissions | Low NOx certified | Retail listing |
| Thermal efficiency | Not stated as a percentage in the listings we readThe listings say best-in-class efficiency without a number. We run it at 82%, the assumption we use for every gas heater on the site, and would revise it if Pentair published a figure we could cite. | Retail listing |
| Cost per million BTU delivered | About $28.36 at 82% efficiencyUS average residential natural gas at $24.09/Mcf (EIA, June 2026). | Our arithmetic |
- Largest common residential gas class, so the fastest heat-up on this site
- Low NOx certified, so it is permitted in the air districts that require it
- Described across listings as noticeably quieter than the older gas designs
- Roughly two and a half times a heat pump's cost per delivered BTU
- 400,000 BTU/hr demands a gas supply most houses were not piped for
- No thermal efficiency percentage in the listings, so the efficiency claim is unverifiable
- Real delivered efficiency in service
- Heat exchanger life against your water chemistry
- Whether your gas meter and line can feed it without an upgrade
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
Pentair MasterTemp 400 Propane Pool Heater
The same MasterTemp 400 with a propane burner, for the large share of pools with no natural gas line. Everything about the machine is the same and one number is not: propane costs about a quarter again more per delivered BTU at US average prices, which makes the heat pump comparison harder for it to win and the speed argument the whole case.
Best for A full-size pool heated on demand, where there is no natural gas
| Rated input | 400,000 BTU/hrInput, not output. | Retail listing |
|---|---|---|
| Fuel | Liquid propane | Retail listing |
| Emissions | Low NOx certified | Retail listing |
| Cost per million BTU delivered | About $35.66 at 82% efficiencyUS average residential propane at $2.674 per gallon (EIA, week ending 30 March 2026). About a quarter more than natural gas for identical heat. | Our arithmetic |
- The largest gas class where there is no gas line
- Same speed as the natural gas version — hours, not a day
- Low NOx certified
- About a quarter more per delivered BTU than natural gas, and over three times a heat pump
- Needs a propane tank and delivery contract, which is a running commitment
- No thermal efficiency percentage in the listings
- Real delivered efficiency in service
- Heat exchanger life against your water chemistry
- Tank sizing for your usage pattern
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
Raypak Digital Natural Gas Pool Heater
The right answer when speed matters more than running cost — a weekend pool you want warm on Friday afternoon rather than one you hold at temperature all season. At the assumptions we publish, gas costs roughly two and a half times what a heat pump costs per delivered BTU, and it will get there in a fifth of the time. Buy the speed if you need the speed.
Best for Heating fast and occasionally, rather than holding a temperature
| Type | Natural gas or propane fired, digital controlThe manufacturer publishes no retrievable specification sheet; figure is as listed at retail. | Retail listing |
|---|---|---|
| Rating convention | Rated by BTU/hr INPUTA 400,000 BTU gas heater burns 400,000 BTU an hour and delivers roughly 82% of it. Do not compare that number directly against a heat pump's output rating. | Published standard |
| Cost per million BTU delivered | About $28.36 at our published assumptionsUS average residential natural gas at $24.09/Mcf (EIA, June 2026) and an assumed 82% thermal efficiency. | Our arithmetic |
- Fast — hours rather than most of a day on a full-size pool
- Works the same in cold air, unlike a heat pump
- Lower purchase price than a heat pump of equivalent real output
- Roughly two and a half times a heat pump's cost per delivered BTU
- Needs a gas line sized for it, which is often the real cost
- Propane instead of natural gas raises the running cost by about a quarter again
- The efficiency this specific unit achieves in service
- Heat exchanger life against your water chemistry
- Whether your existing gas supply can feed it without an upgrade
These need a unit in hand across a season. We do not have one, so we do not have an opinion worth printing on them.
#ad We earn a commission if you buy through this link, at no extra cost to you. It never changes the ranking. How this site is funded. Prices last checked October 18, 2026.
Questions people actually ask
Is the Pentair MasterTemp 400 a good pool heater?
How efficient is the MasterTemp 400?
What is the difference between the MasterTemp 400 natural gas and propane?
MasterTemp 400 or Raypak 336?
- Average retail price of electricity to US residential customers: 18.34 cents/kWh, June 2026U.S. Energy Information Administration · read 2026-09-02
- US residential natural gas price: $24.09 per thousand cubic feet, June 2026U.S. Energy Information Administration · read 2026-09-02
- US residential propane price: $2.674 per gallon, week ending 30 March 2026U.S. Energy Information Administration · read 2026-09-02
- Energy content conversion factors: 3,412 BTU per kWh, 1,036 BTU per cubic foot of natural gas, 91,452 BTU per gallon of propaneU.S. Energy Information Administration · read 2026-09-02
- U.S. Department of Energy pool-energy figures (evaporation share, BTU per pound evaporated, cover savings, recommended temperatures, wind effect)Recreonics, reproducing and attributing the U.S. Department of Energy · read 2026-09-02
- Pool heater roundup: the 8.33 BTU per gallon per °F figure, attributed on the page to Alicia Toedter of Leslie'sBob Vila · read 2026-09-02
Every URL above was fetched and returned content on the date shown. Where a figure is ours rather than somebody else’s, the arithmetic is on the page and on the methodology page. If you find an error in it, we would genuinely like to know.
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