View Full Version : Keeping water in heated troughs warm cost effectively ...

Dec. 13, 2010, 01:19 PM
Hubby and I have a "minor disagreement" on this one and wonder if there is someone on here with an actual physics or scientific background that can offer their comments ...

We have several smaller 20 gallon insulated and heated containers and they are easy and foolproof to keep at a good temperature. The question arises with the larger Rubbermaid 100 gallon trough which is not insulated and has the plug in 2 pronged heater at the bottom

For all of the heated water troughs, when the horses come in at night, I put a thick piece of plywood over them each night to keep the warmth in them as effectively as possible and I find even if I then unplug them it makes a huge differrence as there is a thin crust of ice on them in the morning instead of a thick one

My take on the 100 gallon trough is that if I keep 75-100 gallons in it at all times, once that water heats up to the desired temperature, it will be able to "hold" that ambient temperature for a longer period of time before cooling off and the heater will have to work far less to keep that amount of water at the desired temperature

Hubby's take on it is that if I just kept just 50 gallons in there at all times, we would burn less electricity to heat and keep 50 gallons heated rather than 75 or 100 ...

So - comments?

Does anyone know for sure which method is better and more cost effective??? :confused:

Thanks as always! :)

Dec. 13, 2010, 01:26 PM
I would agree with you... That's just the reason why lakes take forever to freeze and to thaw for that matter...

Bigger body of water, less temperature variations.

Dec. 13, 2010, 01:52 PM
Water has a very high heat capacity. More is better, and also the ratio will be better between the volume and surface area. If the ambient temperature ever comes above freezing, then more water will be the better solution. (If the ambient temperature is always well below freezing, then your husband would be right.)

Insulating the sides would be helpful if you can. Wrapping it in just about anything - dirt, foam, wood, giving it a layer of warmer air, will help.

Dec. 13, 2010, 01:53 PM
I agree with you. Not only will that smaller amount of water freeze more quickly, a full tank with a cover over it has a relatively small air space beneath the cover... Lowering the water level leaves a larger air space between the cover and the water, and that air will cool more quickly than the water.

Dec. 13, 2010, 09:55 PM
You are correct, in that having more water in the tub keeps it at a better temperature than half-full.

Stack straw bales around the base of the tub, and pack the area between bales and tub with straw. Some of the cheapest insulation you can find. The trick is to have an air layer with air space in it, which is why you don't want snow or dirt (no air, direct conduction heat loss). If the horses want to approach from a particular side, duct-tape at least 3 layers of bubble wrap to it. Thick bubbles, not little ones.

Then, for overnight, get a blue tarp, and crazy-glue more bubble wrap cut to fit your water tank on one side. Lay that over the water at night, and then put the plywood on top. It's an extra step that keeps a layer of trapped, warmed air space between the water and the air, with the plastic keeping heat in and the plywood reducing wind loss.

Dec. 15, 2010, 12:18 PM
We lost power last night, and I was sooo glad I had just filled the 100 gal water trough. This time of year, even if it costs a bit more to keep it full, it is worth it for the peace of mind of having water for horses (if you are on a well and water is dependent on power).

I also use several layers of bubble wrap on top at night.

Dec. 16, 2010, 09:49 AM
It's a simple surface area to volume ratio for heat loss, and it doesn't get a whole lot better as the tank gets fuller (more area on sides and the open top gets bigger, too, since the sides are slanted). At a guess, fuller just means you're constantly heating a bigger volume of water. The benefit of a fuller tank is that it takes longer to freeze if the heater is off, and it's harder for the horses to drink it down enough to uncover the heating element.

One place I know the calculations have been done is for water heaters in houses. There, everything else being the same, it takes more energy to keep a bigger water heater tank hot than a smaller one.

Dec. 16, 2010, 12:28 PM
You're right.
FYI, the most recent issue of Mother Earth News had a plan in it for building a passive solar water tank holder/insulator. Might try it as soon as I get my first electric bill. :)

Dec. 16, 2010, 01:45 PM
It would take less energy to heat 50 gallons than 75 gallons, but I don't think tank heaters are sophisticated enough to self regulate.

Dec. 16, 2010, 02:53 PM
When I fill up the bunny cups I fill them all the way as it takes longer for them to freeze. If I wanted to heat them up or melt them it would take longer if they were fuller. More mass to heat up. Boil some water on the stove and see whether two cups boils faster than two qts.
Energy wise I think your husband is right.
Just in terms of husbandry we changed from a 16 gallon to a 100 gallon tank because it does take longer to freeze and is easier to use.

Insulating it would be the way to save heating costs.