Flutterby™! : Hot water heater costs 2008-02-13 02:34:51.275761+00

Hot water heater costs

2008-02-13 02:34:51.275761+00 by Dan Lyke 8 comments

Okay, lazy web: Anyone got an idea on estimating incremental costs of an overly large hot modern water heater? I've been fairly well convinced that a flash water heater isn't appropriate for us, but we need something larger than we've got, and I can't figure out if we go for the 50 gallon, or just spend the extra and get the 75 gallon.

Since the only thing that should impact operating cost difference is the external surface area and insulation quality, and surface area should only go up with the square root of the volume increase, is there any reason to not just go big?

Initial cost is the only problem with big. In fact, some of the bigger gas ones are higher efficiency because they have room for more clever... um... whatever it is they do in there. I went with a 75 and it is very nice, no coordinating dishwashers, washing machines, and showers.

Our hot water heater bit the dust about a year or so ago, and our plumber advised us to go for the 50, as it would be all that a 2-3 person household could ever use. I checked my gut and we paid the extra and went with the 75.

With the 75, we still run out of hot water regularly in the winter--if we'd gone with the 50, I'd be kicking myself.

we have a gas water heater, run showers, wash dishes AND do laundry at the same time with plenty of hot water. it's a 50 gal size that holds up great for a family of 3-4, depending on whether or not there's an extra kid in the house. go for the 50gal! now if you and charlene plan to incorporate kids into the household (foster parenting :>) the 50 gal would still be an efficient investment.

We're going to be replacing our 20-year-old 65 gallon electric hot water heater this month, and will go with another 65 (or 75) gallon one. Even with houseguests and a soaking tub, we've yet to run into a problem of running out of hot water.

We have a 21 gallon indirectly heated water tank. Water is heated in our propane high efficiency boiler which seems to heat very rapidly, it is then piped through a copper coil that heats the water in the tank by conduction. There are only two of us, I hate long showers, though my wife loves them. We have a dishwasher, but almost never use it. We run at a low water pressure, about 30 lbs because we use well water, rather than a municipal supply. We have never run out of hot water.

The size of the tank required depends a lot on the technology. A better rating might describe how much hot water can be produced over time, rather than just the size. You are obviously correct in assuming heat loss is square/cube proportional except for the inlet and outlet connection losses.

In Northern California the boiler necessary for a two stage heater makes no sense, so that's out.

Water heaters should have two numbers, tank size and recovery time, generally expressed as GPH. I read that it's totally reasonable for a high end heater to have a GPH that well exceeds its tank time. However, I can't find anyone who actually publishes the GPH. It may be that at the consumer level it looks like all water heaters are made by A.O. Smith, and they've got a (probably deliberately) confusing set of their own product lines, even ignoring the Kenmore and Whirlpool and whatever relabelings. Seems like a trip over to the local plumbing trade store is in order.

Thanks, all, I think we'll just rearrange so we can fit in a 75 or 80 gallon heater. Charlene likes baths, I like a shower, we do dishes by hand, and we don't necessarily do them in the same order so if I take a shower and go do dishes while Charlene's taking a bath we're probably up to 60 gallons right there.

#Comment Re: made: 2008-02-13 19:44:36.918175+00 by: Dan Lyke [edit history]

#Comment Re: Water heaters made: 2008-02-17 19:00:39.379274+00 by: andylyke

Yeah, the surface loss goes up roughly as the volume ^ 2/3, but I'm guessing that more important it the efficiency of extraction of heat from the hot gasses of combustion (in the gas fired model - the electric model would be 100% efficient { at the point of consumption}). If I were in the market for a water heater, I'd probably rely on the efficiency label they put on them. For comparing gas and electric heaters - 100 cubic feet of mains gas is about 1 therm, and about 29.3 kWh is a therm, so based on your cost of gas and electricity, and the heater's efficiencies, you can draw the economic conclusions. For us in Georgia, gas is about $1/100ccf (Therefore ~$1/therm) and electricity is about $0.1/kWh, or about $2.90 per therm. So an electric water heater has to be about 3 times as efficient as a gas heater to be competitive in dollars. (On the other hand, ecologically speaking, that 1 kWh is obtained by burning ~1 lb of coal, which has a potential heat content of ~.25 therm, so in terms of coal mined, 1 therm from electricity represents about 4 pounds of coal consumed.) And if you have a third hand, you should consider the ecological damage from coal mining vs gas drilling, and so on until you run out of hands.