Heater Questions

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hollywoodfrodo

hollywoodfrodo

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Feb 20, 2018
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Lakewood, CA
We have the Pentair Mastertemp 400btu Gas Heater - 12,000 Gallon Pool - Pentair Variable Speed Pump and Intellichlor40 SWG. We have 3 Pool Floor Returns specifically for use when heating the pool.

We've used the heater several times so far and just trying to get general info. The Pool Setup guy programmed everything so it's just set on what he put it on. Currently, when the heater is turned on the pump is set to ramp up to 2500RPM's. If I'm reading the heater display right the heat temp is set to 104 Degrees??? (Not the pool temp obviously - I assume this is approximately how hot the tube the water runs through gets?)

It seems to take about an hour to increase our pool from 79 Degrees to 83 degrees - is that about right? It seems like a long time and a lot of gas for a 4 degree change. But the water coming out of the returns is definitely nice and warm.

Is 2500RPM's the right speed? Is it better or possible to run it slower so that the water gets hotter before coming into the pool? (I'm not sure how all that works.)

And lastly, the amount of heat that is basically wasted from this beast kills me. There's like a TON of super hot air that pours out of the exhaust the entire time the heater is running. Makes me wonder why they couldn't design a way to use all that hot air to heat the water even more before finally exhausting it.

Anyway, to us a nice swimming temp is 84/85 Degrees and I thought with the beast of a heater we'd be able to get to that faster from a 77-79 degree starting point, but maybe those were lofty expectations. We live in SoCal so weather-wise we should be able to use our pool year round, but the water will definitely need to be heated and I don't know that we can afford to run the heater for two hours a day so that we can swim for 30-60 minutes in the evening.

Any input, thoughts, suggestions, explanations appreciated!

Eric
 
hollywoodfrodo said:
We have the Pentair Mastertemp 400btu Gas Heater - 12,000 Gallon Pool - Pentair Variable Speed Pump and Intellichlor40 SWG. We have 3 Pool Floor Returns specifically for use when heating the pool.

We've used the heater several times so far and just trying to get general info. The Pool Setup guy programmed everything so it's just set on what he put it on. Currently, when the heater is turned on the pump is set to ramp up to 2500RPM's. If I'm reading the heater display right the heat temp is set to 104 Degrees??? (Not the pool temp obviously - I assume this is approximately how hot the tube the water runs through gets?)

You have automation I am guessing. So it manages the water temp and the heater would need to be set to the highest temp possible in order for you to have full range of setting the temp in your automation.

It seems to take about an hour to increase our pool from 79 Degrees to 83 degrees - is that about right? It seems like a long time and a lot of gas for a 4 degree change. But the water coming out of the returns is definitely nice and warm.

For your size/BTU heater, that would seem pretty close to being the correct amount of heat per hour.

Is 2500RPM's the right speed? Is it better or possible to run it slower so that the water gets hotter before coming into the pool? (I'm not sure how all that works.)

If you run it too slow you will have issues with overheating the heater which can damage it.

And lastly, the amount of heat that is basically wasted from this beast kills me. There's like a TON of super hot air that pours out of the exhaust the entire time the heater is running. Makes me wonder why they couldn't design a way to use all that hot air to heat the water even more before finally exhausting it.

Yes this is how these units work. No matter which heater you have you will always lose some heat thru an exhaust of sorts. Seems like a waste but it is not.

Anyway, to us a nice swimming temp is 84/85 Degrees and I thought with the beast of a heater we'd be able to get to that faster from a 77-79 degree starting point, but maybe those were lofty expectations. We live in SoCal so weather-wise we should be able to use our pool year round, but the water will definitely need to be heated and I don't know that we can afford to run the heater for two hours a day so that we can swim for 30-60 minutes in the evening.

If you invest in a solar blanket for the pool you can keep in much of the heat you put into the water when the heater is on. So cover it up after use and hopefully you won't need to run the heater very long to make up whatever heat you lose during the overnight hours.

Any input, thoughts, suggestions, explanations appreciated!

Eric
Click to expand...

See my answers in red.
 
Sounds like it's set up correctly. The heater gets set to 104 when the heater is controlled by automaton so that the heater's thermostat doesn't interfere with the automation control.

The heater is 84 percent efficient. So, you're getting 336,000 btu per hour and 64,000 btu per hour is lost in the exhaust.

Pentair makes a 96% efficient heater, but it's way more expensive.

So, that's 4% loss vs 16% loss. The 84% heater loses 64,000 btu/hr vs 16,000 btu/hr or 4 times as much.

ETi 400 HIGH-EFFICIENCY HEATER - YouTube
 
The minimum flow is 40 gpm. The max is 120. There's an internal bypass, so, anything over a certain gpm just goes through the bypass.

I would say that 50 gpm is probably a good flow rate.

Some pumps allow you to set a flow rate but most only allow rpm, which won't directly correlate to flow.

The flow depends on the rpm and total head loss at the rpm.

The head loss can be roughly estimated from the filter pressure and the flow can be checked against the pump curve chart.
 
Hello,

I have the same heater however our pool is 30,000 gallons and I run my pump at 1,900 RPM regardless if heater is on or not. In one hour my pool will heat up between 1-2 degrees. As a general comparison it appears the rate at which your pool heats up is correct. I will defer to others as per the optimal pump speed. I can only say that from my perspective, the water coming out of my returns is very very warm, but not hot. I would assume the slower the pump speed the hotter the water is coming out of the returns, but conversely you are heating fewer gallons per hour.

Thanks,
Mike
 
You never want to go below the required flow rate because that can damage the heater.

Too high is also not good because the flow speed erodes the copper in the exchanger.

The slower the water goes, the less efficient the heat transfer is because cooler water absorbs more heat than hotter water.

I would stay between 45 and 75 gpm for a 400,000 btu/hr heater.
 
Thanks for the input everyone! Sounds like my heater is doing what it's supposed to. I do want to get the cover on there as I've heard time and time again covering it in the evening will help retain a lot of the heat from the day. We have the cover - just haven't gotten around to cutting it to shape and using it yet. Will do that soon.
 
the time it takes to cut and fit the cover will be LOTS of gas saved. I heat my pool only when temps drop significantly, I keep most of my heat in and only lose like 2-3 degrees at night at most and make that back the next day. My solar cover can raise the temps in my pool over several days of being covered, Ive seen 90 degree water temps in NJ
 

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