Pentair MasterTemp 400: Does it Cost Too Much To Run?

Pentair pool heater best features

Preface- The Pentair Mastertemp 400 is great for large pools, night time dips and chillier climes. No one likes paying for repeat gas so thankfully this heater is highly efficient, more so than smaller units. It’s also easy to operate and reliable. But does it cost too much to run?

If you have been searching through all the pool heater reviews on Google trying to find a low cost solution for heating your pool, then you’ve come to the right place.

What’s the point in having a beautiful pool that you can’t make use of because you risk hypothermia just dipping your toe in it? Unless, it’s just a picturesque show-off garden feature.

After price 2 things are crucial, the time it takes to work, and the running costs. This review answers exactly that.

If you have a large pool and aren’t fortunate enough to live in one of the hotter locales like The OC, Florida or Arizona, then gas pool heaters work best. Heat pumps are quite sore on electricity and they need a lot of warm air to transfer through to your pool. So in colder states gas is the best way to go. Solar is just too ineffective.

This article introduces you to the Pentair MasterTemp 400 one of the most powerful and highly efficient natural gas heaters currently on the market.

What We like

  • Works EXTREMELY fast
  • Small, compact heater
  • Eco-friendly - Low NOX emissions
  • Award winning energy efficiency
  • Not too difficult to install
  • Durable rust proof exterior
  • Rotating top dial pad to suit your plumbing (to face either left or right)
  • Simple set and forget heating controls via digital dialpad
  • Auto shut off to prevent overheating
  • Vast array of safety features and sensors including manual gas shut off for services
  • Comprehensive clear to understand manual
  • 3 year warranty (once product is registered)
  • Suitable for saltwater pools + all pool types, bromine, hard water, high flow pressure
  • Natural gas or propane models


Here are some average prices to compare against. If you live in Phoenix Az you want your water temp to consistently stay at 78º  can expect to pay approx $1384 in gas costs for the entire swimming season. _ but here's the biggie- if you use a pool cover you can end up paying a meagre $96. ASTONISHING. If you want the water 82º  you'll pay $256- SO LONG AS YOU USE A COVER.

w/ cover3/1–10/31$96$168$256
w/ cover4/1–10/31$184$280$408
w/ cover4/1–10/31$320$424$592
Los Angeles5/1–10/31$1864$2376$2904
w/ cover5/1–10/31$168$304$472
Kansas City5/1–10/31$1434$1872$2384
w/ cover5/1–10/31$288$416$544
New York5/1–9/30$1448$1904$2384
w/ cover5/1–9/30$208$296$400
w/ cover5/1–9/30$216$296$384
w/ cover5/1–8/31$123$168$243
w/ cover5/1–8/31$232$328$461
w/ cover6/1–9/30$192$248$384
San Francisco6/1–8/31$1560$1856$2168
w/ cover6/1–8/31$192$320$472
w/ cover6/1–8/31$304$424$552

*Figures based on a 1,000 square-foot, outdoor pool heated with an 80% efficient natural gas heater at $.80 per therm and uncovered for 8 hours per day.

If you're replacing a gas pool heater, you can use the following formula to determine your annual cost savings with a higher efficiency gas pool heater model:

Current Annual Cost x [1 – (Current Efficiency ÷ New Efficiency)]

Other Factors Influencing Running Costs

Different States naturally have different running costs as the cost of natural gas for instance and the climate varies. It will take less gas to heat up your pool on sunny days where the ambient air and humidity is higher. It also depends on high you like the temperature of your pool to be, and whether you leave a pool cover on in between swimming times.

One thing is clear though this is a highly efficient heater and you will wait less time for it to heat up large pools due to the 400 000 btu, and that goes without saying for hot tubs and smaller pools under 20,000 gallons.

If your climate is a bit too northern for your liking you can certainly extend your swimming season for up to 8 more weeks with a powerful gas heater.

A single BTU (British Thermal Unit) can raise the temperature of 1lb of water by 1 degree which means that the more BTUs a pool heater can produce, the quicker the water will heat up in your swimming pool.


Why Is The Pentair MasterTemp 400 Pool Heater So Efficient?

It has a 400k BTU rating. That is currently one of the most powerful residential heater ratings. The higher the rating the quicker your pool is heated up. With this 400 000 btu rated heater you can expect on average a 2 degrees F per hour rise in the temperature of your pool.


Late night swims made possible by Pentair

Does It Cost Too Much To Run?

You can check your State just above for average running costs. But before getting into that, high performance doesn’t mean high running coasts. Pentair have just won the EPA Energy Star award for the third year running. They won this again for their range of high performance energy star rated products that make up the majority of their pool heater sales. If you care about the environment these low emission heaters from Pentair are not only recognized but officially awarded by a government body.

If you have a spa and want it to be boiling hot in as quick a time as possible the Mastertemp 400 will do the job better than anything else. For small pools you can expect to wait less for it to heat up. All in all it’s a win-win.

The MasterTemp series uses a coiled heat exchanger with a combustion chamber as opposed to a traditional heat exchanger with burner. This is what makes it one of most efficient pool heaters as most of the heat actually gets transferred to your pool.

If you want your pool to be heated up in less time and maintained at this temperature whilst using less gas, then a more powerful heat exchanger like this works best. The heat exchanger on the HD and ASME models is made from cupro nickel. This is a more efficient than the copper only models for saltwater pools.

Cupro nickel is also proven to last longer than copper only exchangers as it withstands chemical and hard water corrosion in spas and pool. Heat exchangers like this are more durable and this new metal combination will prolong its life.

The standard model has a copper heat exchanger and costs less than the HD and ASME models. So you can make a saving if you are definitely sure you won't be using salt or hard water and can keep your pools chemistry under control.

The HD and ASME models have upgraded components to add extra durability and cope with high flow water pressure.

How Long Will It Take To Heat Up A Pool?

With a Pentair 400k you are probably going to get an approximate 2 degree per hour temperature rise in a medium sized pool. When starting your swimming season it will take about 2 days to heat a full pool if it’s cold.

If you are starting with a water temperature of 80 degrees in a 30,000 gallon pool on a sunny day, you will get to 90 degrees in approximately 8 hours. -  For smaller pools the time will be significantly faster.

In a nutshell the MasterTemp will heat up any size pool. If you have a pool with a spa it will also heat up both. If your pool is small it will heat up very quickly. Larger pools will naturally need more time.

Gas heaters will heat up your pool up to 7 times faster than a heat pump. Heat pumps also need the outside temperature to be about 104ºF to work. If not they rely on their electric elements (heating coils) which burn electric at a much higher cost than gas.

In warmer states gas heaters can cost more than heat pumps to work. Heat pumps like the Hayward HP21404T are initially more expensive. But if the temperature drops below 50ºF they will not work, and will cost more than gas. It is definitely a nice luxury to have both, you can use the heat pump in the warmer months and switch to gas when it gets colder.

Here is the official heat up stats offered by Pentair for their ASME heater models;

pentair asme heat up times

Will the Pentair 400 be good for a spa or small Pool?

spa heat up times

Absolutely as it will heat the spa up to a high temp very quickly. If you have a small pool that needs heated this will warm it up quicker than anything else on the market. Once heated it will be easily maintained without wasting exorbitant amounts or natural gas or propane.

What Size of Heater Do I Really Need?

If you want specifics the size of a pool heater is determined on:

i)what size your pool is

If you want to wait longer and burn more gas in the process then a lower powered model may be more affordable up front, but it will cost more on the back end as you will need to use more gas. For large pools it will simply be too inefficient.

For small pools the Mastertemp is a dream because it gets the job done quicker and maintains the results without draining your gas supply.

If your pool is on the large side- 40k gallons and up, then a 400 btu rated heater is an absolute must. Hayward also have the universal H-Series which boasts btu ratings of 500k at the top end

ii)do you need it for a pool or Jacuzzi, or both?

If you are powering both a pool and a Jacuzzi you will need a heater with a higher btu rating.

iii) are you using saltwater or hard water?

Cupro nickel (copper nickel plated heat exchanger) as you know prevents corrosion. If you use a pool heater without cupro nickel in saltwater or hard water you will void it’s warranty.

Cupro Nickel (which the mastertemp has) is also proven to last longer than copper only exchangers and prevents chemical and hard water corrosion in spas and pool. It will also withstand low ph, high flow pressure and everyday use.

Pentair pool heaters are specifically designed for heating pools and spas that use chlorine, bromine or salt.

Make no mistake, this is one of the most powerful residential heaters you can buy. If like me you live in a colder state, you will be able to start your swimming season sooner and stretch it out much further. Swimming early in the mornings and late in the evenings will no longer be a problem.

Calculating The Precise Size of Heater You Need

Getting the right size of heater for your pool can be a complicated business. Heater manufactures calculate the btu rating based on the dimensions of your pool and the desired temperature rise.

But there are other factors that can determine the heater size you may not have thought about which include humidity levels (low), night time temperatures (cold), wind speeds and exposure. If any of these are a factor you are going to need a larger heater.

Plus if you plain ole’ just want the temperature warm all the time, you are going to need a larger heater. If you want to get super technical about wind speed you can multiply the Pool Area X Temperature Rise X 12. This equates to about a 1-1/4 ºF temp rise per hour with an average wind speed on the pool surface of approx 3.5 mile per hour.

How is this formula worked out?

Choose your optimum pool temperature

Calculate the average temperature for the coldest month you will use the pool

Subtract this from the desired pool temperature – this determines how much you need to raise

Measure the dimensions of your pools surface area in square feet

The formula will calculate the size of heater btu rating (per hour) that you need to get the job done:

Pool Area X Temperature Rise X 12.

If you want a  1.5ºF rise multiply by 1.5, for a 2ºF multiply by 2 and so on.

Will It Withstand Bad Weather?

This sure is one tough cookie. The exterior handles are rust proof, and the outer shell is a rust proof composite plastic, but it would be best to protect it with a winter cover in the off season.

On the interior the heating chamber is enclosed which will protect the gas orifices from dust and bugs. Anyone who's owned a heater before knows that spider’s webs can clog up the ignitors and stop gas flowing which can leave you scratching your head as to why the heater won't start. It's either call the professionals or break out the toolbox and start investigating.

In the winter you should always drain water from the heater, your pool pump, filter and PVC pipes, to avoid ice from setting in and destroying your equipment. Remember as water freezes in cold conditions it expands and can cause leaks and broken pipes. Generally this type of damage is not covered by warranty.

Are Pentair Pool Heaters To Be Trusted?

Pentair Aquatic systems are giants in the swimming pool, spa and aquatic equipment industry. You may have heard or possibly even own the Pentair Intelliflo 011018 pool pump. It is legendary. They also own Sta-Rite products. Pentair has been around since the 1960's and they are in no danger of disappearing tomorrow. In 2015 they had a revenue of $6.4 Billion with a staff roster of 30 000 employees.

Their range of products includes heaters, automated vacuums, lighting, pumps and filters. You can even control a range of their products via an app on your Smartphone or compatible device. Pentair are arguably the biggest name in the pool industry.

Most of the problems related to Pentair heaters, and almost every other big name brand come from bad installation and saltwater or chlorine contamination due to excessive levels. Ensure you install a back flow valve - read the section "Ensuring your pool heaters longevity".


Installation is fairly straightforward but it is recommended you get a qualified engineer, so if anything does go wrong your warranty is protected. Connect the power, connect the gas, and then the water (schedule 40 PVC) pipes. Everything is very compact and neatly laid out.

There are two water headers to attach to your plumbing. The pipes are 2”. But if you have older plumbing and something like 1.5 inch pipes you can buy reducer bushings from home depot or your local hardware/plumbing store if installing it yourself.

For outdoor installation the unit should not be stored close to windows, doors and air vents. See below diagram.

Pentair 400 btu ventilation instructions

Plumbing Diagram

pentair 400 plumbing diagram

Here’s where it starts to look a little more complicated:

pentair plumbing

I definitely won’t be plumbing this myself, but if you are an engineer it might be right up our street.

Indoor Installation

You CAN'T use this or any other pool heater indoors without a proper ventilation system which requires a specified vent pipe. It’s dangerous to use in enclosed areas like garages or basements without a vent system. Stick to the recommended ventilation clearings in the manual.

Gas Installation

Note the manual says only to be connected by qualified servicemen. Here is the gas pipe sizing for all Pentair heaters;

mastertemp 400 gas pipe sizing

Installation has to be done right. If you don’t understand this diagram, get a service engineer. Wrong installation can be fatal, and snagged or ill fitted pipes will cause gas leaks.

You need to make sure your gas line capacity can handle the 400. If your gas meter cannot handle 4oo btu then the heater will not run correctly. You need the right size of line and meter or the heater may not start, or can fail after initial start up.

If the heater detects it is not getting enough gas it can auto shut down.

You may also find that you have enough high pressure (2psi) coming from the meter, but the line from your street to the meter might need to be upgraded (or the meter could need upgrading to handle the extra gas flow pressure). If you don't understand this check with a gas service engineer/plumber.

Check the diagram above 400,000 Btu needs at least a 1-2 inch pipe for low pressure. There is the option of using a 2 stage process (with 1" pipe and a regulator), you would need to check this with a gas supplier - In the words of Ice Cube,

check yo'self before you wreck yo'self. (Obviously replace yo'self with"gas line"....a young person told me to say that....)

Air Flow Switch + Gas Valve

Can You Do-It-Yourself?

Now for you have-a-go heroes, plumbers or for someone who has done this before, it is not all that complicated. Run a gas line (3/4 inch if less than 10ft but you can go up to 2 inch if running it over 400ft) to the installation site, which should be beside your pool filter. Then run the return line from the filter over to the input of your heater. Finally the output from the heater is fed straight through to the pool at the return fitting. Simples.

The plumbing is on one side of the machine and the electrical and gas outlets are on the direct opposite side, just under the fan. If you understand all the above, can work through the manual, and don't mind voiding the warranty should something go wrong due to poor installation, go ahead. No pressure.

Meet the Digital Dial Pad

The dial pad is simple to operate. After plumbing in the heater this will be the only thing you will be in contact with. It has simple up and down thermostat buttons. It will even tell you when it needs a service as it has a multi function temperature controller which shows if the heater is operating correctly.

mastertemp 400 diapad

You can also lift off the top and flip it so the dial pad faces the other side if it suits your pipe plumbing better. You don't have to take the headers off or replace anything else. Just rotate the top and that sorts out everything.

Mastertemp 400 Safety Features

Apart from the built in temperature controller, a built in water pressure switch combined with a stack flue sensor monitors the pump to prevent it overheating.  The water supply will automatically be shut off if the water temperature exceeds factory set limits.

The full range of MasterTemp heaters are fitted with a direct ignition HSI (hot-surface ignition) device, which replaces the standing pilot light in standard burner systems. Pentair heaters are specifically designed for heating pools and spas that use chlorine, bromine or salt.

Saltwater Tip- Make sure you install the salt cell after the installation of the heater, to prevent super chlorinated water flowing thru the heater. Super concentrated chlorinated water will damage any heat exchanger and especially non cupro nickel elements.

Follow appropriate procedures to balance out your water. If it’s not balanced it will damage any heater and pool surface, and force it to work harder which will result is excessive undue strain and that can only lead to a reduced life span.

Electrical Rating: 60 Hz120 / 240 Volts AC, single phase.

Recommended Actions (probably by an engineer)

If the heater will be placed below the surface of your pool or spa, ensure valves are used in the circulation piping system so the heater is isolated from the pool or spa. To prevent backsiphoning it is recommended that you use check valves. One of the main reasons backsiphoning will happen is once the pump stops a pressure-suction differential can occur.

You should not sanitize the pool with chlorine tablets or place sticks into the skimmer(s). If you do this when the pump is switched off, a high concentration of chlorine can enter the heater, which can potentially cause corrosive damage to the heat exchanger. Cupro nickel or not, high chlorine concentrations can damage the heat exchanger and its switches.

Personal Safety

When servicing the unit there is a manual gas shut off switch. This energy star rated product has certified low nitrous oxide emissions and adheres to stringent air quality standards. A qualified pool heating technician is advised to install the unit, especially as gas leaks can be silent and deadly. Some states require technicians to be licensed.

pentair 400 operating pic

Make sure you install a carbon monoxide tester close to the machine and a temperature gauge is recommended to check the pool is not too hot. On hot days the pool can heat up more than expected.

Never use propane with a natural gas heater or vice versa. A licensed Pentair technician has to carry out a conversion if you want to switch fuel types. Because naturally if you blow yourself and the whole neighborhood up after tinkering with your unit, your warranty will of course be voided.

Conversion is not that pricey should you wish to switch from natural gas to propane or vice versa. Can cost as low as 40-60 bucks and generally requires a nozzle change with a few slight modifications.

Hot Tub Health Risks

Everyone likes to be in a boiling hot spa, and many people I’m sure like to exceed safety regulations and push the limits above 40 degrees. Manufactures recommended no higher than 38 degrees for healthy adults in hot tubs and extreme caution is needed where children are considered.

For pregnant mothers no higher than 38 degrees in the first 3 months of pregnancy is advised as this can lead to foetal damage. But to be on the safe side I wouldn’t go anywhere near this during the first trimester, in fact as far as I would go is dipping in up to the knees. Why take the risk?

Time To Get Techie

Who wants to know how this pool heater works? If not skip onto the next section.

Air and gas is precisely metered into the mixer via orifice plates. The air and gas is channelled through the mixer via a built in blower which directs it to the burner’s flame holder. The flame holder is surrounded by a sealed heat exchanger which discharges exhaust gases out through the flue.

Water is connected via 2” PVC water pipes which flows directly into the manifold/header at the side of the heat exchanger with the standard supplied 2" PVC slip unions. No heat sinks are needed as the outer manifold stays cool. The water flow through the heat exchanger is regulated by a thermal regular and internal bypass which ensures the correct outlet temperature.

The water temperature is set on the main control board, and operated via the dial pad.

water pressure switch inside heater
air flow switch

Happy now? No? Here’s some more juicy engineering specs to wet your appetite.

The heater is controlled by an electronic temperature sensing thermistor inside the manifold adapter inlet. Once it senses a drop in the inlet water temperature (set by the dial pad thermostat), extra power is supplied to combustion chamber via the burner controller which is channelled through a series of safety interlocks.

These switches work in combination inside the interlocks;

A PS (pressure switch) monitors if the pump is running or not. A HLS (high limit switch) opens once the temperature of the heat exchanger outlet rises above 57 degrees (135oF). The AFS (air flow switch) monitors pressure drops and the AGS (automatic gas shut off switch) opens if the heat exchanger outlets temperature climbs beyond 60 degrees (140oF).

A SFS (stack flue sensor) auto shuts down the heater if the flue gas temperature is detected to be above 249 degrees (480oF).

Once there is sufficient air flow the AFS closes the circuit to the HSI (hot surface igniter) which lights the fuel mixture. Once more heat is needed the blower and then the HSI are energized. In 20 seconds time the gas valve opens up and the ignition becomes imminent.

Finally the HIS automatically reverts to monitor mode and watch guards the flame.

This thing has more sensors than a BMW, but they all work to ensure your safety and the longevity of your heater.

How It Works In Layman’s Terms

The 400 is powered with natural gas or propane.  When it’s running water is circulated through the pump and passes through a pool filter and then into the heater. The gas burning in the heat exchanger (inside the energy efficient combustion chamber) heats up the water and that water is fed back into the pool.

The water is constantly turned over until the desired temperature is met. After it reaches this the heater auto shuts down and once the water sensor detects a dip in the temperature it kicks back in again. This makes it extremely efficient.

Who Needs This Heater?

Anyone who lives in a colder state or just plain likes the water to be hot all the time.

This pool heater is top of the range and as such might be overkill for a small pool, but bear in mind once it gets going and the temperature is reached the gas flow will be minimal and the heat exchanger will only kick in once the water temperature drops.

If you want the option of using your pool for a few hours per day, or only at the weekends a gas heater is the way to go. If you aren't using the pool constantly it is more effective than any other heating source. For constant use, 7 days a week heating a pool with a gas heater will be more expensive.

The good thing about gas heaters is that they work well in any type of climate. They are not limited by air temperature and will work on cold days. They also work fast and are great for unplanned off the cusp hot tub dips and pool swims.

Noise Levels

The 400 is touted by Pentair to be a very quiet machine so if you have sunbathers chillaxing by the pool you won’t encroach on their serenity. Or will you? Official stats from Pentair says it runs at 60db. Depending on how quiet you like your "quiet" time then this may be an issue. If you have it a good distance from your pool you may not notice it as much, but to totally minimize the noise you'd need to put it inside a brick enclosure.

How Long Will It Last?

Most of the problems that accompany heater breakdowns are usually due to poor installation and care of the equipment. If yours is installed properly you can expect it to last for 10-15 years and more. If you don’t maintain or regularly check your water chemistry or drain the system in the winter months, you can be looking at a 3-5 year life span. Not a lot for a product priced around $2k.

pentair pool heater

Explanation Of The Different Pentair Mastertemp 400 btu Models

The MasterTemp 400K has a rating of 400,000 BTUs. This is the same basically as 3-4 furnaces in a standard sized home which are generally kitted out with furnaces rated at between 100,000-150,000 BTUs.

The HD (Heavy Duty) and ASME models ratings have upgraded components to prevent corrosion.    The HD (Heavy Duty) model has a CU (cupro-nickel) heat exchanger to specifically cope with saltwater and is more capable of withstanding hard and high flow water. Cupro-nickel is used extensively in marine environments, where corrosion is simply just not an option.

The ASME model exceeds the recommendations advised by the American Society Of Mechanical Engineers. It is similar to the AHRI (Air Condition Heating & Refrigeration Institute) accreditation other manufactures use.

Natural Gas Or Propane?

These models take Natural Gas:

460734 - 300k BTU Natural Gas model

460736 – 400k BTU – Standard model with copper heat exchanger

460805 - 400K BTU/HR (HD) – cupro-nickel heat exchanger for low PH water, heavy use, saltwater, high flow

460775  - 400K BTU/HR (ASME) – beefed up components, such as: thicker CU heat exchanger and metal headers.

461021 -  400K BTU/HR (HD ASME) – bronze headers and cupro nickel heat exchanger

Two of the 400K BTU/HR models take Propane. Here are the model numbers:

460737  - 400K BTU/HR} STD (Standard Model)

460776   - 400K BTU/HR (ASME)

Size & Weight

Most of the 400 series weigh 120-130 pounds and the unit measures approx. 30 X 25 X 36 inches. Due to its small size and rotating top panel installation is pretty straightforward and it can be neatly tucked away without being a major eyesore.

Ensuring Your Pool Heaters Longevity

Many people have vented anger against even the premier pool heater brands like Pentair & Hayward when their heat exchangers have failed. They have cited adamantly that their PH levels were ok and checked weekly. But as most pool industry installation engineers will testify rarely will they see a pool heater model fail due to manufacturer incompetence.

RTM (Read The Manual) – You’ll find this in it - if you have a chlorinator beside your heater it should only be parked on the outlet side of the heater and you should have a back flow prevention device or you will risk trapped highly concentrated chlorine (very low PH levels) feeding back into your heater.

Water levels need to be kept under control. If your PH levels are very low your water has the corrosive properties of acid. This will eat through your heat exchanger and that part alone can cost $500 if you can source it.

Not to mention the damage cause to individuals and your pool, the plaster, vinyl or lighting systems...

How do you keep your PH levels under control?

It’s worth noting that lower PH will do more damage to a heater than higher PH will.

Lower PH effectively creates an acid bath and not only can this cause serious damage to your skin, eyes, organs and general health, but it will also strip plaster, tiles and damage pool lighting. And it will eat up the insides of your Pentair Mastertemp 400 and any other heater on the market if left too long.

After rainfall your pools PH levels can swiftly bounce up or down. Though generally depending on what type of pool surface you have * if alkalinity is within the ranges of 90-120, PH should not dramatically bounce.

It is essential that your water levels are constantly kept in balance and you keep your pool hygenic. Stabilizer and alkalinity has to be placed inline and PH has to be checked daily until levels stay set. PH must be kept within 7.4-7.6 and chlorine has to be over 1.5 as the stabilizer and alkaline is being set.

This can take 1 or 2 weeks of testing and tweaking, and after the ALK is set, PH should generally stay in place during WEEKLY TESTS.

*For salt pools with plaster/peb-tec you ought to test PH TWICE a week, and you may find you have to lower it with acid).

*Fiberglass pools that don’t have a salt system usually need PH to be raised up weekly, and having some soda ash handy will help.

What Water Flow Rate Do I Need To Have For the MasterTemp 400?

You need at least 40 GPM. If you don’t have the required flow the heater may not start and can sit idle if the flow circulation can keep up. If your water rate is higher than 120 GPM a manual bypass valve should be installed and adjusted to an acceptable flow rate.

Can It Be Installed Above Or Below Pool Level?

Yes but the water pressure switch may have to be adjusted. Only recommended to be done by a licensed pool engineer or someone who really knows what they are doing.

What Pentair Could Improve Upon

Seems to be some confusion as whether the more expensive ASME models are needed by pool owners. They are made with a thicker Cupro-nickel heat exchanger and metal headers.

But in reality if you keep your pool chemistry at acceptable levels you won’t need the ASME model. But if you live close to the Ocean you may want to play on the safe side. It also begs the question for the price why are not all their models given the ASME gold standard treatment?

It does get a bit complicated that there is also a HD (Heavy Duty) model and a HD ASME model. Naturally the price goes up as you are paying for a higher spec model and one that withstands corrosion to a better level.

But why not make all the models ASME standard and possibly Pentair could introduce a HD model thus streamlining the whole process and making life a lot simpler for buyers. There are enough choice options already from heater size (btu) to natural gas and propane.

It’s a big investment, your area has to be cold or you really have to like warm water or stretching your swimming season to buy this. Make sure you will make use of it before purchasing.

Recurring gas costs are an issue as is electricity with a heat pump, although this one is out of consumers hands.

Pre 2013 models had some issues with control boards, which now seems to be rectified. Just make sure to register your warranty.

Buying Options + Warranty

Pentair don’t sell direct to the public and prices can fluctuate wildly at retailers. We’ve seen as much as a $500 difference on the same model at competing stores.

A 2 year extended warranty is offered on all MasterTemp heaters once you register the product.


For larger pools the Pentair Mastertemp 400 heater will get the job done better than just about anything else. If you like to spontaneously jump into the hot tub during the day or night without waiting around for hours these 400k heaters are just the trick.

Gas heaters are ideal for quickly heating up pool or spa water and maintaining the desired temperature no matter what the weather is like outside. Fancy a dip in the tub on a freezing cold night in winter? Fire up the Pentair and off you go. You won’t do this with a solar pool heater or a heat pump.

Used it in conjunction with a pool cover your gas bills will be SIGNIFICANTLY even ASTRONOMICALLY lower.

For pools we would recommended it’s at least 30K gallon before ordering one of these. Unless you have very little patience or believe big is better when it comes to pool temperature. Because this is as close to a commercial pool setting as you are going to get.

If you are going to pick between one of the MasterTemp models, it makes more sense to go with one of the HD (Heavy Duty) or ASME models. It costs a few hundred more, but heaters aren't cheap anyway and you'll get more from it in the long run.

If this heater doesn't quite float your boat check out this article on the complete Hayward H Series.

4 thoughts on “Pentair MasterTemp 400: Does it Cost Too Much To Run?”

    • It will certainly be very efficient Josh. It will heat up your water in an extremely fast time, which means you won't have to run it that much afterwards to keep the desired temperature. The Mastertemp 300 will also do the job for you and will save you some money, although in terms of purchase price the 300k base model, is not much different in price from the 400k base model. But the 400k model will get you a whole 100k more btu. That's a heck of a lot of warmth!

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