City-Data Forum Elecric vs Propane hot water (how much, alternatives, furnaces, Lowes)
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09-10-2011, 06:00 AM
 99 posts, read 264,806 times Reputation: 94

My electric co-op offers a deal on Marathon water heaters. They're electric of course. We have two 50 gallon propane heaters plummed in series. We have the first one turned off to save some gas, turning it on when we need the extra hot water for guests or whatever.

We have used an average of 10 gallons of propane a week this summer. The furnace has not been on once, we cook on the grill for the most part which is not on our main propane tank. Usage seemed a little high considering that and I was about to call the propane company to look for a leak. But I thought about the water heaters and did a little math, looking at the estimated cost to operate the heater sticker. It says \$348 estimated annual cost. In very small text below that is says at an "average cost of \$1.23/ gallon of propane.

First, propane will likely never be \$1.23 a gallon again. It's \$2.75 right now. Second, that's 5.45 gallons a week expected average. So now I know where the propane went.

I'm considering scrapping the two propane heaters and going with one, larger Marathon heater.

I did some more math. Many ways are suggested across the web to compare them but the simplest seems to be that one gallon of propane is equal to 27KWH in heat output. So just based on that and the cost of those two fuel sources, the propane costs \$14.85 a week per heater and electric (same amount of water heated) would be \$9.33 at current prices. Add to that the lower standby loss inherant in an electric heater and the even lower standby loss of a higher end, better insulated heater.

It seems I could save about \$5 a week in fuel and avoid the spikes in propane price. What am I missing?

My existing heaters are A.O. Smith Promax and seven years old. They are the lower end of A.O. Smith's line and near end of life anyway.

Does anyone have experience making such a swap? Please skip the tankless discussion. I'll not be going that way.

Thanks

09-10-2011, 06:13 AM
 Status: "C'est la Vie. C'est la Guerre." (set 11 days ago) Location: The Triad (NC) 25,119 posts, read 54,276,481 times Reputation: 26000
**when** the power goes out... the ability to not need electricity to cook or make hot water is invaluable.
The rest is about *how much* hot water is needed.
It is a very rare home or household that will EVER need 100 gallons of hot water capacity.
It is a very rare family that can't (won't) adjust their consumption pattern around a smaller unit.
In this specific instance... at least one gas water heater is already owned.

So?... Don't make any changes until the current water heater(s) have run through their useful life.
The current heaters will probably benefit from some basic maintenance. Do that.

When that time comes... or immediately (if that money is burning a hole in your pocket*)
buy ONE smaller LP water heater (40 gallon should be fine).
---

hth

*or there are actual condition issues beyond maintenance.

Last edited by MrRational; 09-10-2011 at 06:24 AM..

09-10-2011, 06:24 AM
 27,907 posts, read 65,323,142 times Reputation: 17352
I think your math looks correct for the operating costs. That said, I am less sure that even a low end name brand water heater would be "near the end of its life" after only seven years. It would not surprise me if these units are going strong for closer to 15 years -- the better made units like AO Smith generally use the warranty as a selling feature, but they don't really "suck out" the quality in the units warranted for only 10 years vs those warranted for longer...

The other thing that gives me pause is the assumption that switching to electric is an easy jump -- while it is true that the lack of any combustion element means a quality electric unit can be more heavily insulated, the fact is the units your electric company is promoting might not be the "quick recovery" type units, might require some fairly expensive re-wiring, will likely leave you with a chimney that needs to patched at an up charge, and may not really "save" you much depending on your usage patterns and time frame of ownership...

I would certainly cost out the whole project, factoring both the upfront charges and the ongoing operation. I would also give a hard look to all the various alternatives -- tankless, condensing combustion, heat pump, even solar assist. Electricity costs are fairly low now, but most folks predict they will rise faster than costs of fossil fuels -- the "evil" part of the electric company's plan may be to lock you in now and then make out like a bandit as prices rises and you have given away your alternative(s)...

09-10-2011, 12:53 PM
 99 posts, read 264,806 times Reputation: 94
Quote:
 Originally Posted by MrRational **when** the power goes out... the ability to not need electricity to cook or make hot water is invaluable. The rest is about *how much* hot water is needed. It is a very rare home or household that will EVER need 100 gallons of hot water capacity. It is a very rare family that can't (won't) adjust their consumption pattern around a smaller unit. In this specific instance... at least one gas water heater is already owned. So?... Don't make any changes until the current water heater(s) have run through their useful life. The current heaters will probably benefit from some basic maintenance. Do that. When that time comes... or immediately (if that money is burning a hole in your pocket*) buy ONE smaller LP water heater (40 gallon should be fine). --- hth *or there are actual condition issues beyond maintenance.
In the year that we've lived here, the power has never gone out. That's not to say that it can't but it's pretty reliable. If it's out, so is the furnace. I'm certainly not going to get in the shower with the heat off and I'm not suggesting changing the stove. Just the water heating system.

For us, 50 is adequate most of the time, that's why we have one turned off most of the time. The garden tub or four or more showers in the morning requires more. It's a fact that gas fired units of the same relative quality have more standby loss than electric, these are low end, poorly insulated gas units. When both are required, I suffer twice the standby loss that I would for a single unit. I'm considering a switch to a single, high efficency electric tank. No flues, no standing pilots.

Standby loss and fuel choice are the only attckable costs that can be addressed by equipmment selection. It still takes about 500 BTU to lift a gallon water from 50* to 110*. It doesn't matter if that gallon is in a large or small tank, an electric or gas tank. So, if I can get a rope around standby loss, and chose the least expensive fuel choice, that's the best I can hope to accomplish.

You assume that the basic maintenance has not been done. It has and the heater is using the quantity of LP that the manufactrer suggests that it should. However, Propane is more than twice the price now that it was when the unit was installed. Though both energy sources have gone up in price, electricity in the North West has not gone up that much. At \$.064 per KHW, I believe we are the second lowest rate in the country and it's primarily hydro produced here. LP on the other hand is a demand priced fossil fuel.

09-10-2011, 01:13 PM
 99 posts, read 264,806 times Reputation: 94
Quote:
 Originally Posted by chet everett I think your math looks correct for the operating costs. That said, I am less sure that even a low end name brand water heater would be "near the end of its life" after only seven years. It would not surprise me if these units are going strong for closer to 15 years -- the better made units like AO Smith generally use the warranty as a selling feature, but they don't really "suck out" the quality in the units warranted for only 10 years vs those warranted for longer... The other thing that gives me pause is the assumption that switching to electric is an easy jump -- while it is true that the lack of any combustion element means a quality electric unit can be more heavily insulated, the fact is the units your electric company is promoting might not be the "quick recovery" type units, might require some fairly expensive re-wiring, will likely leave you with a chimney that needs to patched at an up charge, and may not really "save" you much depending on your usage patterns and time frame of ownership... I would certainly cost out the whole project, factoring both the upfront charges and the ongoing operation. I would also give a hard look to all the various alternatives -- tankless, condensing combustion, heat pump, even solar assist. Electricity costs are fairly low now, but most folks predict they will rise faster than costs of fossil fuels -- the "evil" part of the electric company's plan may be to lock you in now and then make out like a bandit as prices rises and you have given away your alternative(s)...
We moved here from San Diego where we lived in the same house for 20 years and with three different water heaters. In SD, with that poor water condition, seven years is a heater past it's expiration date. I don't know about A.O Smith but GE will not honor the warranty on a rusted out tank. There is always a "reason" that it rusted out. Poor water quality, maintenance, whatever. Weeks at least to get a decision. It's not worth the hassle on a \$600 appliance. Best case, they replace it and I have the same situation as now. Two heaters burning propane.

When I did the maintenance on the heaters this spring, I pulled the burners out to vacuum the cavity. On the heater that we dont use much, a large pile of rusted chips was sitting on the burner and all around it, obviously from the bottom of the tank. That heater will fail before the snow melts next spring.

MR85245 heater \$949 including tax. Minus the rebate, plus whatever a new 240V circuit costs, 45 feet across the garage from the panel. I can wire it but I have no means to bend conduit so I'll hire it out. Under \$500 I'm sure. The plumbing I can definately do. \$1500 total. If I can't make it pay, I'll junk the heater that leaks first and just run on one until I see signs of it's failure.

09-10-2011, 02:45 PM
 Location: Somewhere in northern Alabama 16,231 posts, read 49,010,202 times Reputation: 25693
I agree in general with your estimates, etc.

There is no need to replace both heaters. That gives you an interesting option. You will want a good plumber that understands the concept I'm about to lay out.

Keep the better of the two gas heaters. Sell the other on Craigslist.
Look on Craigslist for someone selling an electric heater with low usage. Inspect by using a little inspection camera on a wand, or remove one of the sacrificial anodes to eyeball it and inside.

Now you have one electric and one propane. Neither can hold you hostage, as you can select which one you use if you plumb it like this.
You will need six shutoff valves and eight "T" fittings.

Incoming cold - invert a T fitting, shutoff valves on both outlet sides (arms) of the T.
The stem of the T is always your incoming cold. Label the arms of the T and shutoffs " A gas" and "B elec"

Input to gas heater - ANOTHER T, with the base of the T stuck into the inlet port of your gas water heater. Put a shutoff valve on ONE of the arms of the T, label it " C elec > gas ",
connect the incoming "gas" from the inverted T to the arm of this T that doesn't have a valve.

Input to elec heater - ANOTHER T, with the base of the T stuck into the inlet port of your elec water heater. Put a shutoff valve on ONE of the arms of the T, label it " C gas > elec ",
connect the incoming "elec" from the inverted T to the arm of this T that doesn't have a valve.

Output of gas heater - another T with the leg stuck in the hot water outlet of the gas heater.
Output of electric heater - another T with the leg stuck in the hot water outlet of the elec heater.
Outgoing hot - T fitting, shutoff valves on the two INLET sides (top arm) of the T
Bottom of that T is always your domestic hot water out.
Connect the other arm of gas heater outlet T to the elec heater inlet T
Connect the other arm of elec heater outlet T to the gas heater inlet T
Label the shutoff between the gas heater and hot water out "E gas out"
Label the shutoff between the elec heater and hot water out "F elec out"

With that configuration you can:
( X is closed valve, O is open valve
1. Use gas only AO BX CX DX EO FX
2. Use electric only AX BO CX DX EX FO
3. Use the gas as a tempering tank for the electric AO BX CX DO EX FO + gas off
4. Use the gas as a preheat for the electric AO BX CX DO EX FO + gas on
5. Use the electric as a preheat for the gas. AX BO CO DX EO FX
(the electric tank will be too insulated to temper water effectively for the gas heater)

It is best to keep water going through both tanks to prevent stagnation. (avoid configurations 1 & 2 unless you drain the appropriate tank)

09-10-2011, 04:47 PM
 Location: State of Superior 8,546 posts, read 13,073,613 times Reputation: 2678
The future goes to electric, still the most efficient and .,in most parts of the Country , less expensive than gas.... Now when you talk Propane, that's a nightmare! These companies are scamming their customers everyday. They will clam the propane in your tank as theirs , no matter what,and , you will be charged the higher rate always... You may avoid this by buying the tank , but I do not recommend it. Propane is an oil by prodit and can be the most costly, unstable, unsafe, source of energy there is. Stay away from it at all costs,. that's my opinion and my experience. IT was a nightmare in Southern Mi. and they had Nuke power...what was I thinking!... I bought into the scam that gas in all forms is cheaper than electric, quite wrong. I sold my house, one reason was the cost of propane. I could not afford to heat in the coldest months. I was a customer of Amaregas for over 20 years, but , that meant nothing, I was put on cash refills and had to drive 20 miles to their office to pay, no checks , no credit cards.... When I refused to pay the additional cost of the gas difference , they shut me off, and charged 75.00 to turn off as well as 75.00 to turn on.... Remember , these " gas" companies are not regulated, they can do what they want, do not fall for these crooks!

09-11-2011, 03:20 AM
 35,405 posts, read 36,272,417 times Reputation: 13888
Quote:
 Many ways are suggested across the web to compare them but the simplest seems to be that one gallon of propane is equal to 27KWH in heat output.
Electric = 3,412 BTU/kWh
Proapane = 91,333 BTU/gallon

Be 26.7 so you're WRONG!

That's the raw output, you need to adjust for efficiency. The electric is going to transfer 100% of the heat produced to the water, the propane won't.

I have fuel calculator here that allows for efficiency: Fuel Comparison Calculator for Home Heating

Note this is for furnaces and the efficiency is only for how efficient it uses the fuel. Heat loss is not included.

09-11-2011, 05:12 AM
 99 posts, read 264,806 times Reputation: 94
Quote:
 Originally Posted by thecoalman Electric = 3,412 BTU/kWh Proapane = 91,333 BTU/gallon Be 26.7 so you're WRONG!
I rounded.

09-11-2011, 05:23 AM
 99 posts, read 264,806 times Reputation: 94
Quote:
 Originally Posted by thecoalman Electric = 3,412 BTU/kWh Proapane = 91,333 BTU/gallon Be 26.7 so you're WRONG! That's the raw output, you need to adjust for efficiency. The electric is going to transfer 100% of the heat produced to the water, the propane won't. I have fuel calculator here that allows for efficiency: Fuel Comparison Calculator for Home Heating Note this is for furnaces and the efficiency is only for how efficient it uses the fuel. Heat loss is not included.

Thanks for that calculator!.

Electric @ \$0.064/kwh = \$18.76 / MBTU
Propane @ \$2.75/gal = \$37.64 / MBTU

A clear winner.

Last winter, our first in a cold climate, while we were spending \$600 a month on propane, I tripped to the idea that maybe a space heater in the room where we were, would be better than heating the whole house to a comfortable temp. That \$600 was with a malfunctioning furnace. Hopefully this winter will be a little better with the furnace fixed but Propane is much more expensive. I think I'll be using the space heater a little more now that I know the relative costs of both fuel sources. Thanks again.
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