LPG Tankless vs. Electric Water Heater

[Alan L.]

Be sure when calculating your electricity cost to ad in transmission and distribution to the cost if you have it. We get our electricity for about .13 KW but pay close to that again for the distribution and transmission cost. Suffice it say, it makes electricity pricey especially in a tiered system where the more you use, the progressively more you will pay. That does not apply to propane. Here is another "plug" for propane by the propane association

DOE Energy Costs - new - National Propane Gas Association

The 13 cents we are paying now is the total. I just divide the total amount I pay by the number of KWH to arrive at that figure. It comes from an electric co-op.

 

[kenmac]

Cal, just my opinion only, but, If you are going to pay retail & pay someone to install these tankless heaters. It is my opinion that, You would have to use a good amount of hot water for the tankless to pay for themselves.If you used alot of hot water I would say , go for it. On the tank that is in the metal shed, you could cut a small hole in the bottom at the thermostat & turn this unit down when not in use. Once the water is heated in a tank type water heater, It dosen't have to cycle on that often to keep the water hot(if hot water isn't being used.)The pilot light it's self ( if gas) will aid in maintaining water temp. a pilot light don't use alot of gas (mabe 3 C.F.H. if that much ).You also have to remember , that when these tankless water heaters fire , they use in the neighbor hood of 200,000 B.T.U. or more to give that instant hot water.I have installed these units for customers(mostly commerical) but, for personal use, I still have the tank type W.H.

 

[California]

The low duty cycle use on the first two locations would really benefit from on-demand heaters. I am guessing that a very high percentage of your energy cost are from just keeping the water warm.

That's my intuitive feeling but several industry pros have appeared in this thread saying 'it depends...' so I'm still trying to learn both sides of the issue.

Cal, just my opinion only, but, If you are going to pay retail & pay someone to install these tankless heaters. ...You would have to use a good amount of hot water for the tankless to pay for themselves.If you used alot of hot water I would say , go for it.

That's the issue , I have low usage in this mild climate so economy measures might be pointless. I can't decide. Maybe there is little opportunity for a saving.

The gas bill for September (when the cabin was vacant and we used little space heat) was $30. It paid for maybe 30 individual showers and 5 loads of laundry. (We weren't there full time). Spring and fall with the cabin occupied are about $65, and a couple of winter months just over $100, with most of that probably for the cabin's space heat.

Looking at this, I see your point that the conversion cost for these water heaters might never be recovered considering so little potential savings.

You also have to remember , that when these tankless water heaters fire , they use in the neighbor hood of 200,000 B.T.U. or more to give that instant hot water. I have installed these units for customers(mostly commercial) but, for personal use, I still have the tank type W.H.

I wonder if one that serves just a washing machine could be smaller. Also whether the washer needs instantaneous full temp. I was thinking of a simple through-the-wall vented unit (concentric cold air inlet surrounding the exhaust) and installing it myself, so the cost to replace the existing heater shouldn't be too much.

On the tank that is in the metal shed, you could cut a small hole in the bottom at the thermostat & turn this unit down when not in use.

I hadn't thought of cutting a peephole. Good idea! Maybe that's all I need.

CurlyDave, I didn't mean to hijack your thread!

 

[_RaT_]

Cal, just my opinion only, but, If you are going to pay retail & pay someone to install these tankless heaters. It is my opinion that, You would have to use a good amount of hot water for the tankless to pay for themselves.If you used alot of hot water I would say , go for it. On the tank that is in the metal shed, you could cut a small hole in the bottom at the thermostat & turn this unit down when not in use. Once the water is heated in a tank type water heater, It dosen't have to cycle on that often to keep the water hot(if hot water isn't being used.)The pilot light it's self ( if gas) will aid in maintaining water temp. a pilot light don't use alot of gas (mabe 3 C.F.H. if that much ).You also have to remember , that when these tankless water heaters fire , they use in the neighbor hood of 200,000 B.T.U. or more to give that instant hot water.I have installed these units for customers(mostly commerical) but, for personal use, I still have the tank type W.H.

I think you bring up excellent points. A Rinnai model 85 installed is getting close to $2000. That would not include upgrading the gas line if needed. I have the Rinnai model 2424 and while it works fine, I have yet to be convinced that a tankless can keep up with demand when other appliances are turned on. You need electrical power to have hot water with tankless. With todays tank heaters, better insulation quality and slightly better efficiency compared to old tank heaters and much, much cheaper cost to purchase and install especially when a tank was there before still makes a tankless heater a very costly option. Contrary to some posts, I rarely have had to replace a gas (tank) water heater. If you go on vacation a lot, a tank will have a VACATION mode option. My .02 says that while tankless are really great ideas, are well built and probably save some gas, I just personally have not seen it. After two tankless units, I am seriously thinking about going tank type again. Problem is, where do I put it. I'm plumbed for only tankless. Maybe a second tankless but then, I would say my gas bill would be more. Its ironic, I run out of enough hot water with a tankless heater that provides unlimited hot water provided I don't exceed a few gpm and have very rarely run out of hot water with a tank heater that provides high GPM flows for limited durations. I'm still not convinced all applications work so great with tankless.

 

[_RaT_]

I forgot to mention this and it is important. I do want to test my NG supply at my Rinnai heater to be sure I am getting the 199,999 BTU's out of it. If the supply is to low, it would explain some of the reason that my GPM of hot water seems underwhelming. At our house, when someone is in the shower, you do not turn on a sink unless its cold water and there is no way to fill the tub and have a shower going elsewhere, not even close.

 

[Dargo]

I forgot to mention this and it is important. I do want to test my NG supply at my Rinnai heater to be sure I am getting the 199,999 BTU's out of it. If the supply is to low, it would explain some of the reason that my GPM of hot water seems underwhelming. At our house, when someone is in the shower, you do not turn on a sink unless its cold water and there is no way to fill the tub and have a shower going elsewhere, not even close.

That would probably be a good idea. I have one of the 200k BTU units and one of their commercial 240k BTU units. Those along with my pool heater, 4 NG furnaces, 1 50 gallon tank water heater, ovens, and clothes dryers etc. forced me to have my utility company to come out and check my NG flow. They ended up putting in a much larger meter and upping the pressure to the meter. Now, I have enough gas flow. The upstairs of my main house is covered by the 240k BTU Rinnai and there are two showers going at once at least 5 days a week along with a sink or two. The 200k BTU Rinnai is in my pool house and there is only one shower there, but there have been many times that hot water has been used in the sink at the same time without any drop in water temp.

 

[kenmac]

Cal, That $30.00 gas bill probably isn't all gas usage. Here the gas co & power co. charge a fee (if you use gas/ power or not ) just to keep your account active. The fee is around $8.00- $10.00 which is included but, may not be seperated on your bill.

 

[kenmac]

Rat, as you may know this is easy to figure. If you have a nat. gas meter , turn off all other gas equip. except the 1 you are checking. Fire the equipment at full or high fire & clock the hand that turns on your meter. the formula for this is 3600 X dial size divided by sec. per rev. if you have a 2 # system in your home you would add another 11%. this formula will give you the total amount of gas your gas appliance is burning.

 

[Doc_Bob]

If you are only going to use the gas water heater sporadically, then just turn it off when not there. I do this when I go on vacation for a week. Only takes the nat gas heater a few hours to heat it all when I get home. And, in the summer, when my solar heater is running full tilt with long sunny days, I don't even bother to turn on the gas water heater at all, as the stuff from the solar system is 160 degrees!
Bob

 

[MossRoad]

The current price of LPG is far less than $3. Of course, the price of LPG is much more subject to market fluctuation than electricity. Another thing to consider when projecting costs is the fact that tank models have a "standby" cost that tankless doesn't. In tank models, there is a cost in keeping the water hot all the time until it is ready to use. In a tankless, the water isn't heated until ready to use. On This Old House, Richard Trethewey made this contrast, "It's like keeping your car engine turned on and idling all day and night, due to the chance you might need to jump in and drive it."

I have been so pleased with my Takagi that I would never consider using anything else.

Yes, but how many times a day does a tank water heater turn on when you are not home? Ours kicks on halfway through my shower in the morning and stays on for about five minutes after the shower is over. Then it sits there all day. I have never heard it run during the day or night when no one is using hot water. I think if you are frequently not going to be home for a few days at a time, have a vacation home, or live in a restricted water use area, tankless would would make good sense. But for us, home every day, showers in the morning and laundry and dishes at night, a tankless has little advantage over a tank unit.