A gas heater is the right call for a spa when you need heat on a cold night, on short notice, or without waiting on a heat pump that stalls once the air drops. That is the short answer to the question behind almost every search for the best gas pool heaters for spas: a combustion unit burns fuel directly into a heat exchanger, so it works in any weather a person can stand outside in, and it puts a 300 to 500 gallon hot tub from tap temperature to soaking temperature in minutes rather than hours.
What makes spa duty different from pool duty is rarely discussed properly, and it is where most sizing mistakes happen. A spa is a small body of water held at a high temperature, not a large body of water held at a moderate one. That changes three things at once: how many BTU you actually need, how hard the heat exchanger is working, and what your fuel bill looks like every month. A unit rated for a 20,000 gallon pool at 88F is being asked to do something entirely different when it runs against a 400 gallon tub at 103F, and it is worth sizing for the second job.
We went through eight natural gas and propane heaters built by Raypak, Hayward and Pentair, checked the rated output, plumbing sizes, control layouts and review histories, and sorted them against the way a spa actually gets used. Our top pick is the Raypak PR106AENC, and the reasoning is in the sections below along with the trade-offs for each unit. If you are still deciding between fuel types, our [pool heater comparison](https://webcomicsweekend.com/best-pool-heaters/) sets out the wider field first.
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Top 3 Picks for Spa Duty for October 2026
Raypak PR106AENC 105K
- 105000 BTU natural gas
- Purpose-built for spas
- All-copper fin-tube exchanger
- Fanless draft-proof design
Hayward W3H200FDN 200K
- 200000 BTU natural gas
- Spas up to 600 sq ft
- Digital LED self-diagnostics
- Low-NOx certified
Raypak P-R406A-EN-C 406K
- 406000 BTU natural gas
- Digital electronic ignition
- ProTek Shield exchanger protection
Eight Gas Spa Heaters Compared Side by Side for October 2026
| Product | Specs | Action |
|---|---|---|
| Raypak PR106AENC 105,000 BTU Natural Gas |
|
Check Latest Price |
| Hayward H-Series W3H200FDN 200,000 BTU |
|
Check Latest Price |
| Raypak P-R406A-EN-C 406,000 BTU Digital |
|
Check Latest Price |
 Raypak PR156AENC 150,000 BTU Natural Gas |
|
Check Latest Price |
 Pentair EC-462024 125,000 BTU Natural Gas |
|
Check Latest Price |
| Pentair MasterTemp 125 EC-462025 Propane |
|
Check Latest Price |
 Pentair MasterTemp 460737 400,000 BTU Propane |
|
Check Latest Price |
 Pentair MasterTemp EC-462027 250,000 BTU Propane |
|
Check Latest Price |
The table below is worth a second look before you scroll further, because the output numbers alone will mislead you. Three different heaters can all heat the same tub in about the same time if you give them enough minutes to get there, and the real differences show up in set point limits, exchanger material and how the unit behaves on a windy night.
1. Raypak PR106AENC 105,000 BTU Natural Gas Pool Heater – Best Overall for Spas
Raypak PR106AENC 105,000 BTU Natural Gas Pool Heater for Above Ground Pool and Spa Elevations 0–4,999 ft (014779)
105000 BTU natural gas
2 inch connections
Purpose-built for spas
Fanless design
Pros
- Highest average rating among the Raypak models here
- Quiet fanless operation
- Easy self-install that fires on first start
- All-copper exchanger rated for wind and drafts
Cons
- 105000 BTU is tight for large tubs
- Plumbing connections sit close together
- One report of early ignitor failure
This is the only heater in the group that was designed for the job rather than adapted to it. The PR106AENC is listed specifically for above-ground pool and spa use, and everything about the design follows from that brief.
The output of 105,000 BTU sounds modest next to the 400,000 BTU units later in this guide, and for a 20,000 gallon pool it would be. A spa is not. Water has a high specific heat, so a small volume at a high temperature responds quickly, and the review history reflects that: buyers describe steady heating to target temperature and quiet running.
The fanless all-copper fin-tube exchanger is the detail that makes it our pick. Reviewers credit that design with holding performance through falling leaves, wind, rain and downdrafts without needing a fan to fight them, which is exactly the failure pattern that ruins small heaters sitting on an exposed pad in winter.
Polymer headers round out the package and prevent rust staining on the spa surface, which matters more than it sounds when your tub is a fiberglass shell with a visible waterline.
What to check before you buy this model
The first thing to confirm is flow rate. A gas heater needs the pump to move water through it at the manufacturer’s stated minimum, and a spa circulation pump that is undersized for the heater will produce a no-ignition condition even on a perfectly good unit.
Second, look at where your plumbing enters. The water connections sit close together on this chassis, and at least one buyer had to add a straight fitting before an elbow to make the geometry work. Measure before you order fittings.
Where it falls short for spa owners
If you have a large swim spa or a raised spillover tub with a deep basin, 105,000 BTU will get you there but it will not recover lost heat between sessions as quickly as a bigger unit would. Owners running this heater on bigger above-ground pools report fast heating anyway, but a 500 gallon tub at a low starting temperature is a longer job.
There is also a small cluster of early-failure reports, including an ignitor failure inside the first week and one report of internal rust and a leak within a year of light use. That is a minority of the reviews, but it exists, so keep the installation on a proper pad with correct drainage.
2. Hayward H-Series W3H200FDN 200,000 BTU Natural Gas Heater – Best for Large Spillover Spas
Hayward H-Series Natural Gas Pool Heater for Inground Pools 200,000 BTU
200000 BTU natural gas
Spas up to 600 sq ft
Digital LED self-diagnostics
Low-NOx certified
Pros
- Highest average rating in the lineup at 4.1 stars
- Digital control panel with self-diagnostics
- Connections on either side for tight pads
- Low-NOx certified for emissions-restricted areas
Cons
- 200K BTU is oversized for small spa volumes
- Meant for in-ground installs
- 161 pound unit needs two-person handling
If your spa is a raised spillover unit attached to an in-ground pool, this is the heater that matches the way the system is plumbed. It is rated for in-ground pools and spas up to 600 square feet, and sibling models in the same series cover 450, 750 and 1,200 square feet bodies of water.
The control panel is the part owners notice most. A digital LED display with self-diagnostic capability tells you what the heater thinks is wrong instead of leaving you guessing, which is a real advantage when the alternative is a rollout switch that trips at odd hours and gives you nothing to work with.
Flexibility matters more than the spec sheet suggests. Gas and electrical connections can come off either side with a built-in 3/4 inch gas connection, so a pad that is tight against a wall or crowded by a filter vessel is much less of a problem than it would be with a fixed-layout unit.
Low-NOx certification is worth noting if you are in a region with emissions rules, and the hydraulic design is built to reduce pump run time while protecting the exchanger from unbalanced water chemistry.
What to check before you buy this model
Confirm your available footprint against the 33.3 by 32.8 by 30.6 inch body and leave the vent clearance the installation manual specifies. In-ground installations are more involved than above-ground hookups, so plan the plumber’s time into your decision.
Also check the surrounding water chemistry practice. The exchanger protection in this design depends on balanced water, and reviewers who ignore that end up with corrosion complaints on any heater.
Where it falls short for spa owners
Two hundred thousand BTU is a lot of capacity for a typical 300 to 400 gallon tub. It will heat the water very quickly, which sounds like a benefit until you calculate operating cost per hour, and the raw fuel burn for a load this size is the largest on the list.
At 161 pounds it is also one of the heavier heaters here, and that is a two-person handling job on delivery day rather than a solo lift onto the pad.
3. Raypak P-R406A-EN-C 406,000 BTU Digital Natural Gas Heater – Best for Pool and Spa Setups
Raypak 406,000 BTU Digital Electronic Ignition Natural Gas Pool Heater
406000 BTU natural gas
Digital electronic ignition
ProTek Shield protection
249 pound chassis
Pros
- Highest output in the lineup for fast pool and spa recovery
- Digital electronic ignition with spark pilot safety
- ProTek Shield extends exchanger life
- One buyer replaced a 17 year old Raypak with reliable results
Cons
- Recurring drain plug leak reports
- Internal rust reported on one unit
- Parts supplied but installation left to the buyer
This unit exists for a specific configuration: a large in-ground pool with an attached spa or jacuzzi, where the heater has to move heat into both bodies of water. Owners report that the 406,000 BTU output warms a pool and attached spa quickly, which is the entire reason to buy something this size.
The ignition system is the standout feature. Digital electronic ignition with an intermittent spark pilot means the pilot only comes on when heat is called for, so the heater is not burning a continuous flame through the shoulder season while you wait for better weather.
Two design details reduce install friction. The combustion chamber material does not retain residual heat after shutdown, which means you can install the unit without adding a metal heat sink, and the ProTek Shield module is designed to protect the heat exchanger and extend service life.
One buyer replaced a 17-year-old Raypak with this model and reported dependable long-term operation, which is a useful data point in a category where longevity questions dominate forum threads.
What to check before you buy this model
Vent clearance and gas line capacity are the two constraints that will stop a project. A 406,000 BTU load needs a properly sized gas line, and in-ground pool owners are advised to confirm a 1-inch natural gas line is in place rather than assuming it.
Ask specifically about the drain plug at the gas entry side when the unit is installed. That is the single most repeated defect in the reviews for this model and it is worth having your installer check it during commissioning.
Where it falls short for spa owners
A 400,000 BTU heater on a standalone spa is dramatically oversized. You will recover temperature faster than you need to, and you will pay for every unit of fuel that goes into the water.
There is also a durability pattern in the reviews that you should weigh honestly. The drain plug leak, a temperature sensor defect on one installation, and internal rust that ended the life of a four-year-old unit are all reported, and the warranty model supplies parts while leaving the installation labour to you.
4. Raypak PR156AENC 150,000 BTU Natural Gas Heater – Best Value
Raypak 014784 PR156AENC 150000 BTU Natural Gas Heater
150000 BTU natural gas
2 inch water connections
Rated for spas
100 pound chassis
Pros
- Largest review base in the group at 84 ratings
- Two inch hookups suit DIY plumbing
- Quiet combustion once gas pressure is correct
- Stainless steel construction
Cons
- Short warranty on customer-installed units
- Reports of internal leaks in the first season
- Rollout switch trips in windy locations
- External regulator needed on a 2 psi line
This is the pragmatic middle of the lineup, and the one with the most review history behind it at 84 ratings. The 150,000 BTU output is a sensible match for a 300 to 500 gallon spa, and the manufacturer lists it as a fit for above-ground pools and spas.
The two inch water connections are a real advantage for a first-time installer. Standard two inch plumbing is easy to source and easy to join, which matters when you are doing the work yourself rather than handing it to a contractor.
Stainless steel construction and a floor-mount above-ground design keep the unit simple to site. Buyers report fast heating on larger above-ground volumes and steady temperature control once it is running.
The catch is installation quality. Several owners who did not get the gas pressure right report noise or incomplete heating, and the model needs an external regulator when it is fed from a 2 psi natural gas line.
What to check before you buy this model
Warranty terms deserve a careful read. The residential warranty on customer-installed units is short, and it extends to a year only when a certified professional does the installation. That single line item can change which installer you choose.
Check your gas supply pressure and plan for an external regulator if you are on a 2 psi line. Getting this right up front is what separates the smooth reviews from the frustrating ones.
Where it falls short for spa owners
The rollout switch is a recurring complaint in exposed locations. In windy areas it trips and does not always reset on its own, which means a spa that needs heat on the coldest nights is exactly when this unit is most likely to lock out.
There is also a cluster of reports of internal leaks and unit failure inside the first season, plus LCD control boards that go blank and need replacing, with residential phone support described as limited.
5. Pentair EC-462024 125,000 BTU Natural Gas Heater – Best for Compact Spas
Pentair EC-462024 -Natural Gas 125K Heater – Limited Warranty
125000 BTU natural gas
82 percent efficiency
1-1/2 inch plumbing
Pre-mixed combustion
Pros
- Pre-mixed combustion gives fast heat-up
- 1-1/2 inch plumbing suits compact spa installations
- Digital controller is easy to operate
- 82 percent rated thermal efficiency
Cons
- Sold with a limited warranty
- About 29 percent of reviews are one-star
- Listed weight of 20 pounds looks low for this class
If your spa is a small tub with tight plumbing and a crowded service area, this Pentair is built around those constraints. The 1-1/2 inch connection is the key number, and the manufacturer describes it as ideal for smaller bodies of water including spas.
Pre-mixed combustion is what drives the heat-up performance. The burner and air are mixed before entering the chamber, which is why reviewers consistently describe fast warm-up relative to the unit size.
The 82 percent rated thermal efficiency is the highest efficiency figure listed in this group, and on a unit that runs as often as a spa heater does, that translates directly into less fuel per degree of temperature rise.
The control is a straightforward digital display and controller. Nothing about the interface will take you an afternoon to learn, which matters if you are programming it around a swim schedule.
What to check before you buy this model
Ask about the warranty terms in writing before you order. This heater is sold with a limited warranty rather than full coverage, and that distinction matters a great deal on an appliance that is expected to last a decade or more.
Verify the listed shipping weight with your supplier as well. At 20 pounds the published figure looks low for a gas heater in this class, so confirm what is actually arriving and how it is handled.
Where it falls short for spa owners
Reliability is the weakness here rather than capability. Around 29 percent of reviews are one-star, pointing to failures that appear after initial use rather than problems with heating speed or control.
At 125,000 BTU it also has less headroom than you might want for a large tub or a cold-start recovery, and the limited warranty leaves less protection when something does fail.
6. Pentair MasterTemp 125 EC-462025 125,000 BTU Propane Heater – Best for Off-Grid Spas
Pentair EC462025 MasterTemp 125 125,000 BTU Compact Energy Efficient Swimming Pool and Spa Propane Gas Heater for Small Pools Up to 15,000 Gallons
125000 BTU propane
Pools and spas to 15000 gallons
82 percent efficiency
Pre-mixed combustion
Pros
- Explicitly rated for spa service to 15000 gallons
- Pre-mixed combustion for fast heat-up
- 82 percent efficiency cuts propane per cycle
- Compact body suits tight spa pads
- Digital controller is easy to read
Cons
- Lowest average rating here at 3.3 stars
- 34 percent of reviews are one-star
- Listing splits New and Old condition variants
This is the option for a property with no natural gas line. It carries the same 125,000 BTU output and the same 82 percent rated efficiency as the natural gas Pentair above, running on propane instead, which is the whole difference between the two units.
For a rural cabin, a vacation rental, or any site where running a gas line is impractical, propane removes the single largest installation obstacle. You still need a properly sized propane service and an appliance conversion on some installations, but there is no utility line to trench.
The compact footprint and 1-1/2 inch plumbing genuinely help in a tight spa equipment pad, and buyers credit fast warm-up on small bodies of water with the digital controller being simple to adjust.
That said, the ratings are the weakest in this comparison. A 3.3 average with roughly 34 percent one-star reviews tells you that performance is not the problem, durability sentiment is.
What to check before you buy this model
Resolve the condition variant on the listing before ordering. This product appears with New and Old condition options, and which one you receive changes the warranty position entirely.
Confirm your propane service capacity and regulator sizing with the installer. A 125,000 BTU propane appliance has different supply requirements from the natural gas version and the conversion is not always a like-for-like swap.
Where it falls short for spa owners
Propane carries a real running cost penalty. Owners on forums consistently put propane at roughly two to three times the cost per BTU of natural gas, and on a heater that cycles often that gap is the dominant operating expense.
The reliability sentiment is the other drawback, with reliability complaints dominating the negative reviews relative to the performance praise, and at 125,000 BTU there is limited recovery headroom for a large tub.
7. Pentair MasterTemp 460737 400,000 BTU Propane Heater – Highest-Output Propane Option
Pentair 460737 MasterTemp High Performance Eco-Friendly Pool Heater, Propane Gas, 400,000 BTU
400000 BTU propane
Low-NOx certified
Manual gas shut-off
36 by 25 by 30 inches
Pros
- Shortens wait times on cold propane starts
- Best-in-class efficiency for its capacity class
- Low-NOx certification exceeds industry standards
- Manual gas shut-off gives a service safety point
Cons
- Lowest average rating here at 3.2 stars
- Only 36 percent of reviews are five-star
- Overpowered for a typical spa
- Deep in the category sales ranking
If you are heating with propane and want the shortest possible wait, this is the largest propane output in the group at 400,000 BTU. It is built for big water volumes and the reviews describe exactly that, with owners noting how quickly it takes the chill off on a cold start.
The manual gas shut-off is a serviceability feature that gets overlooked. Having a positive isolation point at the appliance means your technician can work on the unit without shutting off gas to the whole house.
Low-NOx certification exceeding industry standards matters in emissions-restricted areas, and the 36 by 25 by 30 inch body is a conventional rectangular footprint that fits most standard pads.
Buyer sentiment is the concern. At 3.2 stars with only 36 percent five-star feedback, this is the lowest-rated unit we looked at, and the one-star share runs well ahead of what the specifications would suggest.
What to check before you buy this model
Work out the propane demand before anything else. A 400,000 BTU propane appliance needs a serious fuel service, and the arithmetic is unforgiving: at roughly 91,500 BTU per gallon of propane, that is close to four and a half gallons consumed every hour the burner runs.
Ask your supplier what detail exists on the unit before you commit. The listing carries a single catalog image, so you have less visual information here than with the other heaters in this guide.
Where it falls short for spa owners
The output is excessive for a typical spa and that is not a small point. You will be buying heat you do not need at a fuel price that is two to three times what natural gas costs per BTU, which is the most expensive possible combination.
Weak review distribution is the other issue, and it sits in a category where repairability matters, since a large propane appliance on a tub that is used a few hours a week is an expensive thing to own and rarely exercise.
8. Pentair MasterTemp EC-462027 250,000 BTU Propane Heater – Best for Indoor and Outdoor Flexibility
MasterTemp Pentair EC-462027 250,000 BTU Propane Gas Pool Heater
250000 BTU propane
Rust-proof exterior
Premix combustion
Rotatable controls
Pros
- Rust-proof exterior targets the main corrosion complaint
- Premix combustion gives fast warm-up
- Rotatable controls can face the service side
- Certified for both indoor and outdoor installation
- Built-in system protection
Cons
- Smallest review base here at 15 ratings
- Polarized results with no middle ground
- 250000 BTU exceeds most spa needs
- Dual certification needs local code confirmation
This is the unit to look at if you want the flexibility of a propane heater and care about corrosion. The rust-proof exterior is aimed directly at the failure pattern that shows up in reviews across this product class, where units left on damp pads develop internal corrosion and leak.
Premix combustion handles warm-up speed, and the rotatable controls are a small practical win that lets you orient the panel toward wherever the service access actually is rather than toward a fixed factory position.
Certification for both indoor and outdoor installation is unusual for a gas heater of this type and genuinely useful if your spa is under a covered structure or in a sunroom-adjacent enclosure.
The evidence base here is thin. Fifteen ratings is the smallest sample in the comparison, and the distribution is unusually polarized with 67 percent five-star and 33 percent one-star and nothing in between, so draw durability conclusions carefully.
What to check before you buy this model
Confirm your local code accepts the dual indoor and outdoor certification before planning the install. Unusual certifications are not universally recognised by every building authority and it is better to know now.
Ask about the built-in safety and system protection features in detail during the walkthrough, because with so few reviews the manufacturer documentation is going to be a bigger part of your decision than owner feedback.
Where it falls short for spa owners
At 250,000 BTU this is more capacity than most spas need, which adds fuel consumption and a larger propane service requirement for no practical benefit on a 300 to 400 gallon tub.
The polarized review pattern is the real limitation. With fifteen ratings you have very little long-term durability signal, and buying a gas appliance on that little evidence is a gamble you should at least be honest about.
Gas Spa Heater Buying Guide
The rest of this guide covers the decisions that come before you pick a model, because a well-chosen heater that is the wrong size or the wrong fuel will disappoint you every season. These are the questions we would ask a pool professional before ordering anything.
How many BTU do you actually need for a hot tub?
Size by spa volume and the temperature rise you need, not by pool gallons or square footage. A 300 to 500 gallon tub is a fraction of a pool, so the same output that would take a pool from 70F to 84F over an afternoon will take your tub from 80F to 103F in minutes.
A rough rule for spa duty: 100,000 BTU handles a small tub, 150,000 BTU covers a typical 400 gallon spa with margin, 250,000 BTU suits a large tub or a spa sharing a loop with a pool, and 400,000 BTU is for a pool and attached spa being heated as one system. The real question is how quickly you want temperature back after a weekend of use.
Every gas heater on this list also has a minimum flow requirement, and undersized pump flow is the number one cause of a heater that will not ignite. Check the manual against your pump’s rated curve before you order, and note that a two-speed pump lets you run high flow for heating and low flow for circulation.
Our broader pool heating guidance covers the sizing rules for larger bodies of water in more depth, and is worth reading if your spa shares equipment with a pool.
Can a pool heater be used on a hot tub at 104F?
Yes, with a caveat that nobody in this category explains clearly: check the rated maximum set point on the specific unit. A heater set to 103F or 104F runs its seals, headers and heat exchanger harder than one cycling around 88F, and the wear accelerates even though the burner is not working any harder.
This is why the polymer headers on the Raypak PR106AENC are worth noting. They exist to handle spa-temperature conditions without staining the tub surface, and that is a spa-specific design choice rather than a pool one.
The practical rule is to buy a unit that is rated for spa service at 104F and then set it to the temperature the tub manufacturer recommends. Most spa manufacturers specify a range rather than a single number, and staying inside that range is the cheapest reliability measure available to you.
Is natural gas or propane cheaper for a spa?
Natural gas, and by a wide margin. Owners consistently put propane at roughly two to three times the cost per BTU, and a spa heater runs far more hours per year than a pool heater does, so that multiplier hits harder than the purchase price difference suggests.
The arithmetic is simple. One gallon of propane contains about 91,500 BTU, so a 336,000 BTU heater burns about 3.36 gallons of propane every hour it runs. On the natural gas side, the same heat content arrives through a fixed monthly service charge rather than a per-delivery refill.
Propane earns its place in two situations: where there is no natural gas line at all, and where the appliance is used seasonally enough that a smaller tank is more practical than running new gas service. If a gas line is already on site for a furnace or a pool heater, the fuel decision is not close.
Which heat exchanger material should you buy?
Cupro-nickel for salt, copper for fresh water, and titanium only if the budget genuinely allows it. Copper is the standard on most of the units here and works well in balanced fresh water, which covers the majority of residential spas.
Cupro-nickel resists corrosion far better and is effectively mandatory for a saltwater spa or one running a salt chlorine generator. Copper can fail in a few years in salt water rather than a decade. Titanium outlasts both and costs considerably more.
Whatever the material, unbalanced water chemistry is what kills exchangers. Keeping pH, alkalinity and sanitizer within range does more for exchanger life than the choice of metal does, and it is the reason manufacturers build corrosion protection into the hydraulic design.
When is a gas heater better than a heat pump?
A heat pump will not operate below roughly 55F ambient air temperature. Below that threshold it either locks out or runs without producing meaningful heat, and that is exactly the condition a spa owner faces on the nights you most want to get in the water.
In shoulder season and mild summer, a heat pump is the cheaper way to hold temperature, and it is far more efficient when it is running. Gas is the answer for cold-weather reliability, on-demand recovery before guests arrive, and properties with no heat pump installed at all.
The practical approach many owners use is both: a heat pump for routine maintenance heat and a gas heater for cold snaps and quick recovery. If you are sizing that combination, size the gas unit for recovery speed rather than steady state.
Which brand is easier to live with, Hayward or Raypak?
Raypak units in this group tend to score higher on quiet operation and hold performance in wind because their fanless copper design does not rely on a fan to fight drafts. Hayward offers the stronger control panel and more flexible connection routing for awkward pads.
Pentair sits in between on control experience, with digital displays and pre-mixed combustion across the range, but its units here carry thinner warranty coverage and more polarized review patterns.
Forum consensus puts repairability and parts availability above everything else. Before you buy, confirm that replacement parts for your specific model number are available locally and check how the authorised service network works in your area. Trouble Free Pool is the resource owners and technicians reach for most when diagnosing a heater that will not fire.
How do pool and spa combination systems handle heating?
The common arrangement runs two separate lines from the equipment pad, with a valve or actuation control diverting flow to whichever body of water you want heated. Owners running combined systems describe heating one body or the other on demand rather than running both together.
A two-speed pump is what makes this practical, since you need higher flow through the heater for recovery and lower flow for circulation. Automation is often layered on top so the spa comes up to temperature on a schedule ahead of use rather than sitting hot all week.
The unit you choose has to cover both bodies of water. That is why the higher-output heaters in this guide exist: a 200,000 BTU or 406,000 BTU heater exists for pool-and-spa setups, while a 105,000 BTU heater exists for a standalone tub.
Can you install a gas pool heater yourself?
No, and the reason is warranty rather than skill. Gas appliances need a permit, a pressure and leak check, and verified vent clearances, and manufacturers reduce or void residential coverage when a unit is not installed by a certified professional.
On the Raypak PR156AENC the difference is explicit: the warranty on customer-installed units is 90 days, extending to a year only with certified professional installation. Pentair units here are sold with limited warranty coverage in the first place, and Raypak supplies warranty parts while leaving installation labour to the buyer.
Budget professional installation rather than treating it as an afternoon project. If you are weighing other ways to spend money on the same tub, our [best swim spas guide](https://webcomicsweekend.com/best-swim-spas/) covers the shell side of the decision, and [solar pool covers](https://webcomicsweekend.com/best-pool-solar-heaters/) are the cheapest efficiency win available to a spa owner.
What should you check when replacing an existing heater?
Footprint and connection side first. Measure the pad and note which side the existing gas and water connections enter from, because a unit with fixed connection geometry will not drop into the same space as one that can be routed from either side.
Then check vent orientation and clearance, gas line sizing, and whether you are reusing an existing pad. A new pad costs more and adds a step, but sitting a heater on settled, cracked concrete is how you get vibration cracks in a heat exchanger two seasons later.
Finally, match the fuel you already have. Converting between propane and natural gas means a new gas valve and regulator and sometimes a permit, and it removes one of the main reasons people replace a functioning unit. If you want the full comparison across fuel types, our [pool heater guide](https://webcomicsweekend.com/best-pool-heaters/) covers the alternatives in depth.
Frequently Asked Questions
What is the best type of heater for a hot tub?
A gas heater is the best choice when you need heat in cold weather or on short notice, because it works below the roughly 55F ambient temperature where heat pumps stop performing. For routine heating in mild weather a heat pump is cheaper to run, so many spa owners use both.
Is it cheaper to heat a pool with natural gas or propane?
Natural gas is cheaper. Propane typically costs two to three times more per BTU, and one gallon of propane contains about 91,500 BTU, so a 336,000 BTU heater burns about 3.36 gallons of propane per hour of operation.
How much propane does a spa heater use?
Divide the rated BTU by about 91,500 BTU per gallon to get gallons per hour. A 125,000 BTU propane spa heater burns roughly 1.4 gallons per hour, a 250,000 BTU unit about 2.7 gallons per hour, and a 400,000 BTU unit close to 4.4 gallons per hour.
Can I install a pool heater myself?
You should not. Gas appliances require a permit, leak and pressure testing, and correct vent clearances. Manufacturers also reduce warranty coverage on customer-installed units, with the Raypak PR156AENC limited to 90 days unless a certified professional performs the installation.
Can a pool heater be used for a hot tub?
Yes, but check the rated maximum set point on the specific model. Running a heater to 103F or 104F accelerates wear on seals, headers and the heat exchanger compared with cycling around 88F, so choose a unit rated for spa service at your target temperature.
Is Hayward or Raypak better?
Raypak units in this comparison score higher on quiet operation and resistance to wind because their fanless copper design does not need a fan to fight drafts. Hayward offers a stronger digital control panel with self-diagnostics and more flexible connection routing for tight equipment pads.
Final Verdict: The Best Gas Pool Heater for Your Spa
The Raypak PR106AENC is the best gas pool heater for spas because it is the only unit here designed around spa service rather than adapted to it, with a fanless all-copper exchanger, polymer headers and a self-install-friendly layout. For a raised spillover spa on an in-ground pool, step up to the Hayward W3H200FDN and its digital self-diagnostic panel. If you have no natural gas line, the Pentair MasterTemp 125 propane is the compact option, with the usual warning that propane costs two to three times more per BTU.
Whichever you choose, size it to your tub’s volume and your required temperature rise, get a certified professional to install it, and keep the water chemistry balanced so the exchanger outlives the warranty. Our [gas water heater rankings](https://webcomicsweekend.com/best-gas-water-heaters/) cover a different but related category if you want to see how combustion equipment compares on other home duty.