Help with heating our pool...

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M

Monkey's Mom

0
Aug 29, 2011
135
North Fort Worth, TX
My daughter is having a birthday party this Saturday. The temperatures this week are supposed to be in the 70's (highest 79 on Thursday) with Saturday being 63 :x We are going to heat our 18,850 gallon pool for the first time for her party. We do not have a solar cover. How long with a 400,000 btu heater will it take to heat the pool from 60 (what it currently is, although I hope it is warmer after a week in the 70's) to 82? I want to make sure we get the pool warm enough to enjoy but don't want to heat it longer than I really need to. I have also thought about buying a liquid solar cover just for the party to keep the heat in as I am heating it up but I have read bad reviews.

Thanks in advance!
 
Try this:

http://www.aquacal.com/images/heat-time-ws.gif

I calculate 8.6 hours to heat it from 60 to 82, though it will probably take a little longer if ambient temperature is around 70F. Recall that 1 BTU is required to raise the temperature of water by 1 degree F (from 39-40F), so the calculation is easy. Just multiply the number of gallons by 8.5 lbs/gallon. BTW, that will require roughly 3.4 million BTU of heating, which roughly corresponds to 34 therms of natural gas. Look at your recent gas bill to see how much this will cost.
 
Hmm, so 8.6 hours to 24 hours?! I better err on the side of caution and start heating it sooner rather than later because it MUST be warm enough for a bunch of 9 year olds to swim for her party or I'm dead meat :hammer:

I don't know how much therms are? This is our last bill...

BILLING INFORMATION:

PREVIOUS BALANCE 123.27
PAYMENT RECEIVED 23-JAN-2012 123.27

CURRENT GAS CHARGE TOTAL 127.70
CUSTOMER CHARGE 7.50
RIDER WNA 9.42
CONSUMP CHRG 16.2 @ 2.51160 40.69
RIDER GCR 16.2 @ 4.32680 70.09

TAX/FEE CHARGE TOTAL 11.78
RIDER FF @ 0.05990 7.65
CITY SALES TAX @ 0.01000 1.38
RIDER TAX @ 0.02037 2.75

CURRENT CHARGES 139.48

TOTAL AMOUNT DUE 139.48
 
24h will be fine. I estimated the minimum amount of time based on the size of your pool. Ours is larger and it usually takes about 15h or so to heat it within that range. So, unless your heater is not actually putting out 400K BTU, your pool should heat up much more quickly. Just make sure to dial in 82F on your heater and it will maintain that temp.

I cannot understand your gas bill since they don't provide the units. Nevertheless, you can roughly estimate the amount of gas you will need to heat up your pool by determining the number of BTU needed. Divide by 100K to give you the number of therms. The efficiency of your heater (unless it is very new) is probably around 82%, so you need to multiply by 1.2 to give you a better estimate (e.g. 34 * 1.2 = 41 therms). Unfortunately, it's almost impossible to read utility bills these days, especially with all the tiers, surcharges, etc. Just divide the total number of therms by the total bill and this will give you a reasonable estimate of how much they charge per therm.
 
ok, one more time. We should do a sticky on how to calculate this stuff!

400k BTU heater at 85% efficiency should put out ~340k/hr

1) convert gallons of water to weight

18,500 gallons x 8.33 pounds per gallon = 154,105 pounds of water

2) You want to put 22 degrees in 154,105 pounds of water

154,105 x 22 =3,390,310 BTU/hrs

3) Divide by the BTU output of the heater

3,390,310/340,000= 9.9 hours

So, it will take around 10 hours. May be a little longer since you have no solar cover. Any wind will accelerate heat loss a bit as the pool heats. A solar cover is a must when heating a pool :wink:

You should use around 40 therms of gas.
 
HELP!!! We have started heating the pool for the party tomorrow. We started at 12:00. Pool water was 64. I researched and it said to allow the sun to help heat the pool so we did and it got to 71. We covered the entire pool with a tarp just now but the temp has dropped down to 70. How am I ever going to heat this for her party? Am I fighting a dead end battle? We have the pool temp set at 85 should I raise it? Would that produce hotter water? The RPM is 1750. Should I raise that? Lower it?
 

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Yes the heater is running and the water coming out in the pool is warm but not hot. The spa is warmer than the pool. It is still at 71. WTH?! Our pool is only 6 months old so the heater is practically brand new. Shouldn't it be working better? How low RPM would heat it best? I read low speed for heating but can't find how low?! I am doomed :cry:
 
Whats the air temp? You need a solar cover, really. It's march 2nd. Your losing heat about as fast as it's going in probably. Not sure on RPM thing. i havea single speed I run at 3700. Sorry imnot more help. It's really early in the year to try and heat a pool.
 
Air temp right now is 54. It is supposed to be 62 tomorrow. I'm debating canceling the entire party. I don't think this is going to work. The tarp covers the pool completely as well as the spa and overflow. It is rated 6 mil. I would have bought a solar cover but by the time the temp (which has been in the high 70s low 80s) dropped for tomorrow it was too late to get one big enough to cover my pool.
 
I increased the flow to 2410 from 1650 to see if that would make a difference. I am wondering if heating the spa to 95 (30 minutes) and then circulating that hot water in the pool for 30 minutes then heating another spa full of water to 95 would help it heat faster as a larger body of hot water would be circulating with the cool water to get the temperature up. I'm not sure that makes sense but it does in my desperate head right now. I need a beer.
 
The deal with water flow and any pool heating system is that the greater the difference in temp between the heater and air temp, the less efficient the heater will be in transfering the heat it generates to the water flowing through it. After all, the air and wind going over it is taking some of that heat and if I remember my high school physics right...the heat transfered follows an exponential curve based on the difference of the temp of two objects. So, if you have a high heat object...you want water going through the heating element fast enough to grab most of that heat before air and exterior factors takes it. If water flows too slow, most of the generated heat is lost. If water flows too fast, then the heater will cool down and have only a mild difference between it and the water meaning that you're moving a lot of water for very little gain and moving of water itself through a long stretch of pipes can cool it...resulting in essentially no pool temp rise. When you first setup a heater, you should get a good idea of what the optimal water flow speed and then set your automation system to run slightly lower than that to allow for good performance even during suboptimal conditions.
 
I wanted to update my post for those that might be interested in how much it actually cost and how long it actually took to heat our pool.

We started heating the pool at noon the day before the party. The water temp was ~64 degrees and the outdoor temp was in the low 70s. It heated fairly quickly ~2 degrees an hour until the sun set and then the temp started dropping. We covered the pool with a large tarp. The temp didn't increase much over night, maybe 1-2 degrees all night long. The next morning, with the tarp still in place, the outside temperature was 63 but the sun was out. It quickly heated from 75 to 88 in ~3 1/2 hours. It took ~22 hours to heat the pool from 64-88. The water for the party was awesome! We kept the pool heated until 6 pm so ~30 hours.

February 2012 our gas bill was $139.88 (the month before the party)
March 2011 our gas bill was $106.07 (the month of the party the year prior)
March 2012 our gas bill was $137.55 (the month of the party)

The weather was a lot warmer this March than it was in 2011. That being said, I still think it only cost $35-40 to heat the pool for 30 hours. I am quite surprised that it was that inexpensive. I was expecting a gas bill $200-300 from what I have researched. We will be having another heated pool party for our 5 year old next month! It was the best party I have hosted and can't wait to host many more!
 
Thanks for the update. We're finishing up our pool build and it's nice to have an idea what to expect costwise from our heater. There's a lot of great people and great information here but I think the vast majority of users only employ their gas heaters to heat their spas, which I don't own. Heat pumps, which can take several days to accumulate the demanded temperature rise seem much more common. Your update was very informative with respect to what deg/hr to expect. Thanks! I'm online ordering a solar cover as I type this. Our plan was to only heat the pool on the weekends in late March and all of April. Now I'm actually humoring the idea of using the heater to maintain a ~72°F temp 24/7. Then we could bump up the temperature to 80-82°, 3-4hrs before we wanted to swim. I'm hoping the solar cover gives me enough temperature rise during the day and restricts sufficient temperature loss at night that the gas heater rarely turns itself on.
 

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