What does it cost to heat a tank of water with gas?

[Christien]

Just a ballpark. $1? $10? $100? I know rates differ in different areas, but I just want an idea. We'll be filling the non-heated pool soon for the summer, and I'm thinking of running the hose from the laundry tub to put in a tankful of hot water, so we can kick-start the heating process. Last summer with just the solar blanket it was almost 2 weeks until it was warm enough to swim in.

I'm guessing a tankful of water couldn't cost more than $5 or so worth of energy - if we run out of hot water, it takes maybe an hour and a half for the tank to fully heat up. How much gas could that possibly consume? Maybe $5 worth? The cost of the water is irrelevant, because we need the same amount of water to fill the pool. It's just a question of the addition gas cost for hot water.

[pete3799]

I think that would be rather expensive. How many gallons (liters) are we talking here?
How about some copper coils over a wood fire?

[stomachmonkey]

Average home water heater is ~50 gallons.

You don't say how large your pool is but a 10x10 ft that's 6 ft deep is ~5,000 gallons.

How many tanks of hot water do you think you'd need to go thru to make a difference?

Me thinks a lot.

[Rick V]

Might be cheaper to drop a few dipstick heaters into the water.

[Mark Henry]

That would be a lot of tanks to feel any effect at all.
My buddy sells simple solar pool water heaters that fit on a roof, etc. Even a small panel makes a big difference. Another buddy made his own out of black pipe and it sits on his shed.
Both use the pool pump.

[Tim L]

Many people heat there pools with gas' depending on your heat loss it can get expensive. I don't think your water heater will do much 50 gallons out of 20,000+??

[Christien]

It's a 60 gallon/227 litre tank. The pool is circular, 16 foot diameter, but we only fill it up about 2.5 feet, so both our kids can play in it. We can't use the filter system because the water level isn't high enough.

[Tim L]

The problem is the pool temp will be at equilibrium with the outside air in just a day or two and unless you constantly heat the pool it's not going to work.

[Christien]

Originally Posted by Tim L

The problem is the pool temp will be at equilibrium with the outside air in just a day or two and unless you constantly heat the pool it's not going to work.

Not exactly - that was the problem last year. The outside air temperature was in the high 60s, but the water temperature was in the high 50s/low 60s, and took almost 2 weeks to match air temperature.

[island911]

Yeah, evaporation is often cooling the water, beyond ambient.

you can't get close to the answer w/o knowing the temp difference and the cost per BTU.

[stomachmonkey]

Originally Posted by Christien

It's a 60 gallon/227 litre tank. The pool is circular, 16 foot diameter, but we only fill it up about 2.5 feet, so both our kids can play in it. We can't use the filter system because the water level isn't high enough.

~3750 gallons.

~60 tanks @ 60 gallons per

$300 @ $5 to heat a tank.

The killer really is 90+ hours just to heat enough water.

So assume you won't fill the entire thing from the water heater, maybe a 1/3rd?

Still 30+ hours of heating water.

Seems like a pain in the ass to me.

I'd do as someone else recommended, DIY solar heater.

[Tim L]

cost / btu could be 1c /1000 btu at the lowest NG, up to 3c for LP. that's 8c to heat 1000 gal 1 deg. for NG. and 24c for LP. So to heat 4000 Gal up 10 deg. thats only $3.20, but the real problem is the heat loss of the pool. You will need to heat it up every day.

[Hugh R]

Besides the cooling at the surface, the Earth is the biggest heat sink in the World (no pun intended). I think you would see zero temperature rise at the rate the water heater pumps hot water out, and the air/Earth sucks it away.

[Zeke]

I can't do the formula, but the difference in the water temp with 60 gallons of hot water won't be much, IMO. You'd be better off building a wood fire and running some copper through it.

Looking at the BBQ, all the copper and fittings and then the cost of the propane, that looks silly.

Maybe you could score a used on demand unit and use it for the pool.

BTW, we must use a couple of full tanks of hot water daily. That's for 2 adults. If it was 5 bucks a tank, we'd be doing something else. I'm guessing less than a dollar per tank.

[stomachmonkey]

Originally Posted by Tim L

cost / btu could be 1c /1000 btu at the lowest NG, up to 3c for LP. that's 8c to heat 1000 gal 1 deg. for NG. and 24c for LP. So to heat 4000 Gal up 10 deg. thats only $3.20, but the real problem is the heat loss of the pool. You will need to heat it up every day.

Yeah but he's not heating the pool, he's using the water from his water heater which is going to be ~120 degrees?

So is it ~$32.00 if he fills the whole thing from the water heater?

Cheap enough but still sounds like a pain.

Personally I'd never turn down the opportunity to spend the day on a DIY project, read: drinking beer, using tools, wife leaving you alone cause you are doing it "for the children".

[Tim L]

Yeah that will be one really hot pool for a few hours!

[Tim L]

water temp 35-40 degrees at 1.3GPM. 1.3GPM*60Min*18 hours = 1400 gallons of hot water from one tank.

That's about right it should take 5.5 gal of LP. at 90% efficiency.

[MotoSook]

Very simplified calculation, to raise your volume (16' diam by 2.5' deep) water 10F.

Specific heat water = 4.187 kJ/kgK
Specific Weight 62.43 Lbs./Cu.Ft
1 KJ/Kg*K = 0.00023886 Btu/(lbm*F) --->1.00010682 Btu/(lbm*F)

Water Volume Ft^3 = 502.4
Delta T (F) = 10
Cost/Dth = $3.50
Cost to heat water = $1.10
Heater Eff= 60%
Actual Cost= $1.83

Most heaters are not that much more efficient than 60%, and we ignore loss everywhere. So it's somewhat ideal.

[MotoSook]

Give you a real world example, we have a 28,000+ gallon inground pool. To heat it from 60F to 85F and maintain 85F for a month, it probably cost me $300-$400 from Thanksgiving through Christmas when the kids were off school.

You will have losses during your ramp up from 50 to 80 degrees. Your water probably comes out of the faucet at 50 degrees during the spring. So assuming 50 to 80 is fair. It's about 314,000 Btu/10F to heat the water in an ideal world.

Your pool is about 1/10th of my pool and you'll be heating it during a warmer ambient period...you're looking at less than $100, and more than $10. That give you the order of magnitude you looking for?

[Tim L]

It's about 314,000 Btu/10F to heat the water in an ideal world.

I think your math is off. 28,000 gal * 8lbs/gal *1btu/lb/deg*10deg= 2240000 btu/10 deg