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Home Repair - - If it ain't broken, don't fix it. Otherwise look here.
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Posted by Pete on September 2, 2006, 1:02 am
Hi,
I have a new pump/heater installation. All are Pentair products - filter, a
new 1/2hp pump and a Minimax 100 natural gas heater, supplied as a kit from
a good pool dealer. Everything is working fine - very strong flow from the
pool, through pump, filter and heater, then back to the pool. Heater
ignites and stays lit, burns strongly. However, the water isn't getting
heated.
I noticed the 2" header on the heater includes a bypass valve. This is a
small plastic disc held in place between the two halves of the header by a
spring. The spring seems to me to be surprisingly weak, especially
considering how well the pump works. This was the first thing that came to
mind, so as a test I added a small spacer to the valve spring, effectively
increasing its compression slightly. It made no difference.
So, my questions are; how long should I expect the heater to be running
before I can tell there is heated water? I've waited a few minutes. Does it
take a long time for the heat to penetrate the water headers in the heater?
I would think a few minutes would be more than enough. Has anyone
experienced a pump that is just pumping too powerfully for the heater to be
effective with the volume of water? Is it common for the bypass valve to let
a lot of water bypass the heater (I still think this is the most likely
cause). Is it possible the heater headers are blocked (tho it's a new
heater)?
Any help would be much appreciated... I'm running out of ideas! Thanks.
Pete
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Posted by Richard J Kinch on September 2, 2006, 3:50 am
Pete writes:
> So, my questions are; how long should I expect the heater to be
> running before I can tell there is heated water? I've waited a few
> minutes. Does it take a long time for the heat to penetrate the water
> headers in the heater?
I hope you don't have some naive idea about pool heating.
Your small unit only delivers 80,000 BTU/hour. Let's say you're piping 50
gallons a minute. That's 50*60 = 3000 gallons per hour. 3000 gallons
weighs about 25,000 lbs. One BTU is one degree F per pound of water, so
the the temperature differential of your heated water will only be
80,000/25,000 = 3.2 degrees F above the pool inlet, hardly perceptible.
It's not going to feel like your household hot water is running into your
pool.
You will bankrupt yourself buying gas to heat your pool. Did your "good
pool dealer" tell you that?
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Posted by Pete on September 2, 2006, 12:01 pm
Thanks for the info. I know it'll take a long time to heat that volume of
water; when I said "before I can tell there is heated water", I just meant
by feeling the outlet pipe at the heater, not the pool water. I should have
been more clear. I still think I should be able to discern *some*
difference between the inlet and outlet pipes after the heater has been
running for a while. Another thought occured to me overnight, one that also
might explain the design of the bypass valve. I think the heater currently
has an airlock. If the water pressure were equal on both sides of the
header, as it should be, the valve would not operate. But if there is an
airlock in the main heated part, the water will pass through the bypass
valve. So I suspect there is probably an air release valve or plug in the
other side, in the return header. I'll check... I hope so!
Thanks again.
Pete
> Pete writes:
>
>> So, my questions are; how long should I expect the heater to be
>> running before I can tell there is heated water? I've waited a few
>> minutes. Does it take a long time for the heat to penetrate the water
>> headers in the heater?
>
> I hope you don't have some naive idea about pool heating.
>
> Your small unit only delivers 80,000 BTU/hour. Let's say you're piping 50
> gallons a minute. That's 50*60 = 3000 gallons per hour. 3000 gallons
> weighs about 25,000 lbs. One BTU is one degree F per pound of water, so
> the the temperature differential of your heated water will only be
> 80,000/25,000 = 3.2 degrees F above the pool inlet, hardly perceptible.
> It's not going to feel like your household hot water is running into your
> pool.
>
> You will bankrupt yourself buying gas to heat your pool. Did your "good
> pool dealer" tell you that?
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Posted by Richard J Kinch on September 3, 2006, 1:20 am
Pete writes:
> I think the heater currently has an airlock.
That would be odd. Pool circulation lines often get air going through.
The heater should not be capable of air locking.
Surely this thing could not burn gas constantly (as you report) without
water also going through it and not overheat. It must have an
overtemperature shutoff.
I think you're just way overestimating what 80K BTUs feels like in that
much flow. Or maybe just hesitant to accept that this unit isn't big
enough to heat your pool, and if you had one big enough, you couldn't
afford to fuel it.
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Posted by Pete on September 3, 2006, 2:24 am
Well, I stripped it down, checked everything over, even tipped the heat
exchanger on it's end, then reassembled. It worked! I guess I'll never know
what the problem really was, but it works just fine now. It raises the temp
of the pool by about 3degF every hour. At 77F I took a dip - bliss!
Wife returns from a trip tomorrow. She'll be pleased.... I hope!
Pete
--
-
> Pete writes:
>
>> I think the heater currently has an airlock.
>
> That would be odd. Pool circulation lines often get air going through.
> The heater should not be capable of air locking.
>
> Surely this thing could not burn gas constantly (as you report) without
> water also going through it and not overheat. It must have an
> overtemperature shutoff.
>
> I think you're just way overestimating what 80K BTUs feels like in that
> much flow. Or maybe just hesitant to accept that this unit isn't big
> enough to heat your pool, and if you had one big enough, you couldn't
> afford to fuel it.
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