Hayward H400 Gas Pool Heater Review: Too Much Heater?
A Hayward H-Series 400,000 BTU natural gas pool heater review covering coverage up to 1200 sq ft, low NOx certification, gas line sizing and who should size down.
Four hundred thousand BTU covers a very large pool, and the gas line is the part people underestimate.
The verdict: The H-Series at 400,000 BTU is the size Hayward specifies for pools and spas up to 1200 square feet, and gas heat is the only technology that will raise a large pool quickly on a cold morning. Buy it if your pool is genuinely large or you want a spa heated on demand. Skip it if your pool is average sized, because a smaller H-Series costs over a thousand dollars less and a heat pump costs far less to run.
Hayward H-Series Natural Gas Pool Heater for Inground Pools, 400,000 BTU
~$5,099
A 400,000 BTU natural gas pool and spa heater with a digital LED control panel, low NOx certification and gas and electric connections on either side.
Check price on AmazonSpecifications
| Output | 400,000 BTU natural gas |
|---|---|
| Coverage | Inground pools and spas up to 1200 square feet per Hayward |
| Control | Digital LED display with water temperature monitoring |
| Gas connection | Built in three quarter inch connection, left or right side |
| Emissions | Certified for low NOx |
| Fuel | Natural gas, with other models available for other fuels |
Specifications above come from Hayward's published specifications. Treat pricing as approximate, since Amazon pricing moves.
What it does well
- Gas heat works regardless of air temperature, which is what separates it from a heat pump on a cold spring morning.
- Four hundred thousand BTU raises a large body of water fast enough that on demand heating becomes realistic rather than theoretical.
- Connections on either side make it far easier to drop into an existing pad without repiping.
- Low NOx certification, which several jurisdictions now require and which is worth confirming against your local rules before buying anything else.
Where it falls short
- Running cost. Gas heat is the most expensive way to heat a pool per degree, and a heater this size can consume gas at a rate that surprises people the first month.
- The gas supply is the hidden project. A 400,000 BTU appliance needs a gas line and a meter that can actually deliver it, and undersized supply is the most common installation problem with large pool heaters.
- This is not a homeowner installation. Gas piping, venting and combustion air are licensed trades work, and getting it wrong risks carbon monoxide.
- Oversizing a heater for a small pool wastes money twice: once on the purchase and again on short cycling.
What owners report
Published owner reports describe strong, fast heating and a control panel that is easy to live with. The recurring theme in negative reports is not the heater but the installation: undersized gas lines, insufficient combustion air and clearance problems appear repeatedly, and in most cases the resolution was a plumber or gas fitter rather than a warranty claim.
The second consistent theme is running cost, particularly among owners who heat without a cover. A pool cover is repeatedly described as the single change that made gas heating affordable, because most heat is lost from the surface overnight.
Who it suits
- Large inground pools, or pool and spa combinations where the spa is heated on demand.
- Cold climates and shoulder seasons where a heat pump cannot keep up.
- Anyone who wants to heat a pool quickly rather than gradually.
Who should skip it
- Average sized pools, where a smaller H-Series does the job for over a thousand dollars less.
- Anyone whose priority is running cost, where a heat pump is several times cheaper per degree.
- Properties without an adequate natural gas supply, which is a survey question before it is a purchase question.
Alternatives worth considering
Hayward H-Series Natural Gas Pool Heater for Inground Pools, 250,000 BTU
~$3,999
Hayward rates this one for pools and spas up to 750 square feet, which covers a very large share of residential pools, and it costs eleven hundred dollars less. Sizing down is usually the correct decision.
Check price on AmazonDR. Infrared Heater DR-1100HP Full DC Inverter 110,000 BTU Pool Heat Pump
~$4,199
A heat pump moves heat rather than making it, so running costs are a fraction of gas. It heats slowly and loses effectiveness as the air cools, so it is the right answer for maintaining temperature and the wrong one for heating on demand.
Check price on AmazonRaypak 266,000 BTU Digital Electronic Ignition Natural Gas Pool Heater
~$3,179
Nearly two thousand dollars less for a mid sized gas heater with electronic ignition, so the pilot only lights when heat is called for. A sensible middle option for a normal pool.
Check price on AmazonKeep reading
- Heat pump vs solar pool heater
- Heater size calculator
- Hayward H-Series 250,000 BTU review
- Raypak 266,000 BTU review
- DR. Infrared DR-1100HP heat pump review
- Pool water temperature explained
This review draws on published specifications, manufacturer figures and the consensus of verified owner reviews. We have not tested this product ourselves, and we say so rather than implying otherwise. As an Amazon Associate we earn from qualifying purchases.
Frequently Asked Questions
What size pool heater do I need?
Sizing depends on pool surface area, the temperature rise you want and how exposed the pool is to wind. Hayward rates this heater for up to 1200 square feet and the 250,000 BTU model for up to 750. Our heater size calculator works it out from your own pool dimensions rather than a rule of thumb.
Gas heater or heat pump?
Gas heats fast in any weather and costs a lot to run. A heat pump costs a fraction to run and heats slowly, losing capacity as the air cools. If you want the pool warm on a specific afternoon, gas. If you want it warm all season, a heat pump. Our heat pump versus solar heater comparison covers the third option too.
Can I install a gas pool heater myself?
No. Gas piping, venting, combustion air and the electrical connection are licensed trades work, and errors here can produce carbon monoxide. Most jurisdictions require a permit and an inspection for a gas appliance of this size, and doing it unpermitted can void both your insurance and the warranty.
How much does it cost to run?
Enough that a pool cover changes the arithmetic completely. Most heat loss from a pool happens at the surface overnight, so heating an uncovered pool means paying to warm the sky. Our pool cost calculator will estimate it for your pool, and our solar cover comparison covers the cheapest way to reduce it.
Is 400,000 BTU overkill for my pool?
For most residential pools, yes. Oversizing costs more up front, and a heater that satisfies its thermostat quickly can short cycle. The 250,000 BTU model covers pools up to 750 square feet, which is a large pool by residential standards. Size from the calculation, not from the biggest number available.
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