This a bit involved, so work through this with me ...
The easiest way is to contact InyoPools online or call them877-372-6038
The goal is to have a heater that has enough capacity to heatthe pool to your desired level in a reasonable amount of time.Maintaining that temperature is a lot easier once the pool is up totemp.
First, the capacity of most pool heaters are rated in BTU's orBritish Thermal Units. One BTU is the amount of heat required toraise the temperature of one pound of water, one degree F. Andsince there are 8.33 pounds per US gallon it takes 8.33 BTU's toraise one gallon of water, one degree F.
Now let's calculate:
1. Determine the number of gallons in your pool (G).
2. Determine the amount in temperature that you want to raisethe pool temp (the easiest way to figure this is to use the airtemp as the minimum and the desired pool temp as the maximum)(Delta T).
3. Calculate the number of BTU's needed (BTU) per gallon ofwater by multiplying step 2 x 8.33. Multiply this number times thegallons of water in your pool (G). This is the number of BTU's toraise your pool temp from the minimum to desired temp.
4. Determine how FAST you want to be able to go from the minimumtemp to the desired temp (in hours) (H).
5. Divide the total number of BTU's from step 3 by the hours instep 4 to yield the BTU'S per hour that your heater will need todeliver.
6. Multiply Step 5 by a error factor of 20% and add to step 5.This is approximately the size of heater that you will need.
Example:
1. Assume pool volume, G = 10,000 gallons 2. Assume 80F desiredpool temp and 60F air temp. Delta T = 80 - 60 = 20F 3. BTU's pergallon x Delta T: 8.33 x 20 = 166.6 BTU's per gallon. BTU/Gal xGallons (G): 166.6 x 10,000 gal = 1,666,000 Total BTU's. (Wow,seems like a lot!) 4. Assume I want to be able to warm the pool intwo days of continuous operation = 48 hours. 5. Total BTUs / Hours:1,666,000 / 48 = 34,708 BTU's per hour. 6. (BTU/Hr x 20%) + BTU/Hr:34,708 x 0.20 = 6,941 BTU's 6,941 + 34,708 = 41,649 BTU's perhour.
Now, most pool heaters come in a round number of BTU's like50,000, 100,000, 150,000, etc. You should select the closest sizeto your needs (usually on the higher side is best).
Hence, for this example, a 50,000 BTU heater would be more thanadequate.
Obviously, you could also work these calculations backward todetermine what Delta T you could handle given a certain size heaterand pool size.
... SUGGEST YOU NOT SIZE A HEATER BASED ON THE ABOVE ARTICLE !!!So sorry, I find so many exceptions (wrong statements andconclusions)... This novice article/ suggestion is a nice try butmisses the mark and should not be used to size a pool heater.
Firstly there are different design conditions for pool watertemps, and different methods, which must be used depending onwhether the heater is a gas (i.e. natural, naphtha, propane) or anelectric resistance or heatpump.
Most people are likely to use natural gas due to the low cost ofthis fuel. Heat pumps can be about the same operational costs orcheaper, depending on your gas and electric rates in your area. Inmy area a heatpump is at a par with the cost to operate a naturalgas heater. (Considering a 4.0 C.O.P.)
Calculating a pool heat loss is involved for sure and one mustcalculate evaporation, radiant losses and convection losses(calculation performed within the evapo-transpiration rate).Conduction can be said to be about 3% as a standard so thiscalculation is not needed to be input as a variable, but should beadded to the calc at some point for the conclusion. All thesecalculations are done against a varying outdoor ambient(temperature, humidity, wind) condition.
Without a pool cover the losses can be up to 3 times that ofusing a pool cover (Lower wind across the pool surface is a lowerrate of loss). Normally it's a factor of about 2-2.5. In the caseof a body of water, the convection (wind) is the "driving force�behind the evaporation portion of the formula's calculation. So oneshould also pre-determine whether a pool cover is to be used beforecalculating. (Typically a pool without a cover will require twicethe btuh for pool water maintenance (twice the heater sizing) andwill naturally take longer hours for initial heating.
Anyone not using a pool cover and heating a pool is ludicrousand will pay for it. Note that with a pool cover, the cover remainson the pool 24 hours a day except for the time the pool is usedwhich can be about 3 hours for most residential pools. Evaporationaccounts for about 70% of the pool heat losses so pool covers do agreat job as water vapor is trapped below the cover and thus so isthe heat (a saran wrapping of 1 mil would do the same as a vaporbarrier).
For a gas heater sizing you can design with it in mind to letthe pool water temperature drop and turn on the pool heater atwhatever day you want to use the pool. This sizing will then bebased on the number of hours you want to wait for the pool to heatup. It will also be based on the starting water temp and final swimtemperature you want. There will be the water volume to heat plusthe ambient losses during the hours of heating, plant room, exposedpiping losses, etc. (which can be about 8%) occurring during theheat up time. (This method, I think, is what the above article wastrying to get to, but sorely missed de-rating the heater (you haveto figure it's 3-5 year efficiency not it's new efficiency), forgotabout the on-going heat losses to the ambient and failed to mentionadding piping/plant room losses, activity losses, with or without apool cover usage.
The article above is very miss leading as it does not correctlyconclude the proper gas heater size... Heating efficiency; I knowsome mfgrs. Say they have 99% efficiency, but this is not apractical truth when measured in the field. Plus there is theexchanger losses which build up (water heated over 40 deg C willprecipitate iron, magnesium, calcium, etc.) so fouling of theexchanger (loss of BTUH output) does occur at faster rates thanwith heatpump s. I suggest you always use a 75% output gas btuhagainst any gas heater mfgr's claim.
For heatpump s it's very different. These are sized to themaintenance of the pool temperature for the estimated hours thepool is covered and estimated hours the pool is uncovered. Swimmingactivity also is an important equation to add, as this activityaccelerates the pool heat loss (accelerates evaporation, plus waterlosses from swimmers) while un-covered. If anyone tried to size aheatpump on the volume guestimate above you'd end up with a hugeheatpump and the initial cost would be prohibited. (You�d never buya heatpump based on this guestimate using the miss-leading volumemethod, where-as in some parts of the USA and other worldcountries; the heatpump is the only way to go). Heat pumps requirethe correct detailed calculation for the heat loss of a body ofwater that utilizes the items mentioned above in this article withevaporation calculated from the convection and other factors in aformula that calculates the water pressure difference to that ofthe air with a database of 24-hour historic ambient lowaverages.
Having said it's very different for Heat pump sizing methods andcalculations, it doesn't have to be... I happened to size my gasheater using the heatpump sizing formula; i.e. the only correctcalculation for determining pool heat losses; surface heat lossbased formula, and sized my heater with the input data that: thepool stays covered 24 hrs a day except 3 hours a day for swimming.I ended up with a very small 100,000 btuh heater that does the jobgreat.
Now having said this let me also include that heat pumps arealso set up differently than gas heaters typically, unless you usethe accurate heat loss method described here-in to which I referand not show..sorry. Heat pumps are set up to be able to run asmany hours a day as they need, and to only turn on once a day. (soheat pumps are always simply maintaining the pool temp at aconstant, (generally) and these amounts of heat are relativelysmall. I used this same set-up for my gas heater, so it simplymaintains the pool temperature I have set. (always ready for me tojump in whether it's day or 3 am!) You don't need to have the poolheated at 3 am, as the mass of water has a great retention with acover, so you do allow it to reach your set temp and then wait forthe following day; during sunshine (higher ambient temps for highereffeciency) to bring back the set temperature.
To help think about heat loss from a body of water (swimmingpool) consider a well, lots of water; say 10,000 gallons and youheat it, and it stays heated for long periods of time as thesurface is say only 2 meters across. Now take the same watervolume; say 10,000 gallons, spread it 1/2" thick across a field andwait one day: it's all evaporated and gone! The heat loss for thewell was minimal, the heat loss for the field of water; tremendous.So surface water calculation is the only true calculation to usefor a pool, with a check on the warm up time (if you plan to letthe pool water drop a day or so, then raise it, then drop it, etc.)Pools with big volumes and small surface areas lose less heat/ hrand require smaller heaters to maintain the maintenancetemperatures.
Take a hot cup of coffee... let it stand in a wind protectedplace...takes a long time to cool down. Now take the same cup ofcoffee and start blowing ambient air on it;(like a pool with windat it's surface) now lots of heat loss, and the temperature cancool up to 2.5-3 times faster..(The wind (convection) acceleratedthe evapo-transpiration! Add a swizzle stick in the coffee(swimmers in a pool) and you further accelerate the rate of radiantand evaporation losses.
This is why using a "volume based heat requirement formula" asdescribed above is not correct, even if you do add these minorcorrections mentioned here-in. The lack of pool cover mention isthe articles biggest err...
I'm sorry to not go on with providing the correct calculationformula and many other details, but thought one reading thisarticle should be made aware, this one is not to follow...
Note; most economically sized heating plants will require about3-3-1/2 days to provide initial warm up (considering about 82-85Deg F) and be proper for the best operating costs. For myself, Ican't see swimming in pool water less than 86 deg F and we keepabout 89 Deg F. most of the time!(old folks)
pool man
Interestingly enough, poolman, for rough estimates, the formulaat the top of the article is accurate enough. Since I can't buy a103356.741 BTU heater, the above formula gives me enoughinformation to make an informed decsion on what size heater to buy.Given the length of your response, and the fact that you don'tprovide your actual formula, I am left to assume you sell poolheaters. Do you service the WNY area???
A thought added by robtig1:
I think that both of these answers have equal merit.Essentially, the raw volume btu calculation needs to be done notbased on the delta T (change in desired temperature), except whendetermining the time taken to initially heat the pool, but rather,the raw volume btu calc needs to be applied to the heat lossprinciples as mentioned by poolman's response.
In short, I think it is the rate of heat loss that needs to bedetermined and then take that delta T and multiply etc.. by the8.33 and volume etc etc... A simple average day experiment will letyou know the change in temp you wish to achieve. Just heat yourpool up, and see how much it cools down during a 24 or 48 hourperiod. This will give you a simple version of pool man's verycomplicated assessment of heat loss through evaporation, line loss,etc..
My purpose of these calculations is to assess the size of asolar heater needed to warm up my pool. I did a simple spreadsheet,and even with a good 12 hours of sunlight optimistic I fear that myinput at such a low BTU rating will hardly dent the temperature ofmy pool. I am calculating on 6,600 btu per hour output on a vacuumtube assembly with 60 tubes. Initially I thought that number to behigh, but on my 140,000 litre pool it only warms it up 0.18 degreesF per day. I feel i must be doing something wrong as I should notneed an acre of solar panels to heat my pool. I would be happy if Icould even add 1 degree per day to my pool. If anyone has anyadvise on this, I would be happy to hear it!!
RobTig1
The calculations used in the 1st part are the same calculationsand numbers used in Ordini's Pools web page. Ordini's continues ontheir page to give information on surface area and losses, as wellas cost comparisons between various available heater styles.
Aarc
Solar heaters will NOT heat your pool to a swim temp. They are asecondary heat source only. You need 400,000 or more btuheater.
Paul: I have an in ground 12 by 24 foot pool with a 30kw gasheater. It raises the temp about 1 deg C in two hours. BUT in allbut high summer [in south u.k] thr ground losses through the poolwalls can drop the temperature 2 degress C overnight even with apool cover and home made 1 inch thick foam slabs laid on yop og thecover.
So.. if your builder didn't put insulation round the pool sides/ floor, which mine hasn't got, then [as i do] you either pay thegas bill consequences or only use the pool when the groundtemperature has hotted up. This year 2012 its been unusually coolhere, i've only just started using the pool in May, purely due toheat loss probs to the ground mentioned above.
And yes I made my own on-top slabs using polystyrene 8 by 4 footslabs encased in horticultural grade plastic sheet and seam weldedwith a hot air gun designed for the purpose, around 100 pounds forthe gun. So my slabs cost me far less than the 1000 poundscommercial ones would have cost.
oh and btw, its feb 2013, i know now that the gas heater is onlytransferring 15kw to the pool water [rather than 30kw] this ispurely because the heat exchanger i inherited, is running at halfits labelled rating, because the manufacturers spec. likes to lookgood. with an inlet temp. of around 70 centigrade it can onlytransfer 15kw. so beware, err on the side of choosing, arounddouble the heat exchanger rating, or double check that theinlet-to-pool temperature difference [and water flow rate] willachieve the required heat transfer.
re. robtig1, in Wales uk we only really get lots of sunoccasionally, and the prob with the collectors is that they producemaximum energy when the sun's already heating the pool anyway. Soin midsummer long days yes it can add a fraction of a degree c,,..but it tends to get lost overnight or by subsequent dull days.
I have about 10 square metres of the black ribbed rubberycollectors, the pool area is 30 square metres. I'd say I need atleast 30 sq metres to make much difference over all. and my pool isunder a huge plastic greenhouselike structure, the collectors areat 60 degree angle inside that enclosed area, and pick up more heat[or rather, lose less heat to the wind] than if they were outdoors.Over all I'm not impressed by the manufacturers claims of 5 or 9degree increase. Not in the average uk summer anyway.
