Speaking of Pool Heaters

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On Wed, 3 Nov 2010 16:13:21 -0700 (PDT), snipped-for-privacy@optonline.net wrote:

This is from page 20 of the Sta-rite gas heater installation book.
"The filter pump should run continuously when the heater is on, and for at least 15 minutes after the heater is off."
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The instructions on my Raypak talks about the dual timer:
"To operate the heater with a time clock, connect the timer to the fireman's switch connection in the heater's wiring. The time clock should be of the dual switch type and set to shut off the call for heat to the pool heater 15 to 20 minutes prior to shutting down the pool pump."
Jim
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OK, I stand corrected on what Jandy has to say.
Here's what Jandy has to say on the subject from the installation manual for one of their similar heaters:
"If you install a time clock to control the filter pump operation, it's recommended that the time clock have it's own low voltage (fireman's) switch to turn off the heater before turning off the pump. The switch should shut off the heater about 15 minutes before the filter pump shuts off. This will allow for a more efficient operation by removing any residual heat contained in the heat exchanger back to the pool."
I think the important thing here is the REASON for the recommendation. Jandy is not saying shutting off the pump and heater at the same time is going to destroy the control panel or destroy the heater. Only that it allows for more efficient operation by allowing the remaining heat from the heater to make it to the pool instead of being wasted. Similar to a forced air heating system where the blower continues to run after the burner shuts off so as to not waste the remaining heat. In the grand scheme of pool heating, I'd say this little bit of heat is insignificant.
The pool here with a Jandy was installed by one of the largest installers in the area and it has a single switch timer. The pump and heater turn off at the same time. It's been running for 5 years with no problems. When it shuts off, there is no evidence of the heater, pipes, etc getting hotter than they do during normal operation. If that's all it took to ruin the heater, what would happen when a breaker tripped or you had a power outage? When it shuts off, the heater is full of water at 85 deg. IMO, and apparently Jandy's too, there isn't enough heat left in the heat exchanger metal to raise that water temp high enough to cause any problems.
If I was doing a new install though, I would agree that I'd use a two switch timer, as all it requires is a timer with that capability and it does capture a tiny bit of extra heat.
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On Thu, 4 Nov 2010 05:44:43 -0700 (PDT), snipped-for-privacy@optonline.net wrote:

You can still feel heat coming out of the pipe for about a minute after the heater shuts off with my Sta-rite. I agree 15 minutes is overkill. I do bet you will boil the water in the pipe if you shut them both off at the same time. That will typically be the high spot in the system so the hot water will not migrate away by convection. My pump runs about 10 minutes after the heater goes off. The pump is on a solid state relay and there is a fat capacitor across the LED gate that holds it up.
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On Nov 4, 1:58 pm, snipped-for-privacy@aol.com wrote:

If that happens, don;t you think I'd be hearing gurgling, ie sounds of boiling? Also, if you could heat the water that hot, I would not expect Jandy to say they recommend having the pump run longer to aid in efficiency. I'd expect them to say that it's mandatory. A heat exchanger is there to do transfer as much heat as possible. Meaning, the heat from the combustion gasses passes through it to the water on the other side. You then have a temp gradient across the metal, combustion gas temp on one side, ~85F on the other. I just don't see that metal having enough thermal energy in it after the flame goes out to heat the 85F water that's inside to 212F. I'd guess that it might get to 125 or so tops.
But now I'm curious. Next Spring I'm going to do a simple test. Let the heater run to get it to normal temp. Then shut it off for 10 mins and turn it back on. I'll put a temp probe at one of the returns and see how hot that first burst of water is when it comes out.

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If that happens, don;t you think I'd be hearing gurgling, ie sounds of boiling? <snip>
== I have. You might call or e-mail them.
Jim
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JimT wrote the following:

I seem to remember that many years ago, my then FIL had a pool heater (250,000 BTU) for his above ground oval pool. It took about 1 hour to raise the water temp 1 degree. Does that sound right now?
--

Bill
In Hamptonburgh, NY
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That would depend on the weather but yes.
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On 11/2/2010 8:32 AM, willshak wrote:

gallon pool, that would be right. Not counting losses which can be appreciable.
Jeff
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Yes you are correct....in Jim's case (small pool / big heater) he might get ~2+ degs per hour. In ground pool heating is a SLOW, expensive process. :(
pool capacity (gals) x 8.3 / heater capacity (factored by estimated efficincy) = ~ water temp degs rise per hour.
Pool users / owners can get an idea of heat losses by meaursing pool water temp over time in various conditons (cover / no cover, etc)
Where is the pool located? Depending on local environment, a pool cover might be enough to prevent freezing along with running the pool a few time per day to bring "warmer" water into the pipes & filter.
But is $250 (someone check my number) for a refill, worth the potential freeze? How about shutting down for the winter?
cheers Bob
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Yes you are correct....in Jim's case (small pool / big heater) he might get ~2+ degs per hour. In ground pool heating is a SLOW, expensive process. :(
pool capacity (gals) x 8.3 / heater capacity (factored by estimated efficincy) = ~ water temp degs rise per hour.
Pool users / owners can get an idea of heat losses by meaursing pool water temp over time in various conditons (cover / no cover, etc)
Where is the pool located? Depending on local environment, a pool cover might be enough to prevent freezing along with running the pool a few time per day to bring "warmer" water into the pipes & filter.
But is $250 (someone check my number) for a refill, worth the potential freeze? How about shutting down for the winter?
== Were in central tx and it's a pool/spa and we use the spa all year. Not sure what the $250 is. I doubt I'll ever have to run the heater to prevent freezing. Normally I just turn the pump on to keep the water running. I throw a blanket over the exposed plumbing too. During the coldest months we've been averaging a couple of freezes. When the water gets into the '50s or so I just stop running the pump (unless it freezes). But freezing isn't much of an issue here and I probably shouldn't have brought it up. <g> Thanks.
Jim
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Sounds right, to me. Almost not worth the bother. And a lot of money in natural gas, too.
--
Christopher A. Young
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http://www.poolcenter.com/heaters_facts_about4.htm -----
- gpsman
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wrote:

http://www.poolcenter.com/heaters_facts_about4.htm -----
- gpsman
Thanks. Makes me wonder if my solar blanket is enough.
Jim
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Probably.
http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic=13140 -----
- gpsman
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wrote:

Probably.
http://www.energysavers.gov/your_home/water_heating/index.cfm/mytopic 140 -----
- gpsman
= Probably. As it is, we just had our first really cold front and reality just hit me. The pool is going into it's normal winter mode. I'm switching to the stationary bike and weights today but the heater and blanket did get me into November by one day this year.
Thanks again.
Jim
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