LPG Tankless vs. Electric Water Heater

[LC Brewing]

All the newer units I've seen have a 0.4 or 0.6 GPM "set point" for flow - low enough for the low-volume washers and such. As I said in my responses to the code post, I've been extremely happy with the Rinnai. I've had no issues with lack of flow through multiple uses, and no problems with outlandish energy costs.

The issues I've seen with using recirculation of any kind that actually circulates through the tankless heater are shortened life of the tankless unit (Rinnai cuts the heat exchanger warranty in half when used in such an arrangement) and decreased efficiencies. There is a minimum amount of BTUs expended for the thing to operate regardless of how much it really needs to heat the water, so you might liken heating the recirculation loop to using a blow torch to light a candle.

I had the Bosch unit running for the first four months in the house and had no recirc loop setup. When I switched to the Rinnai, I added the recirc loop with a 6-gallon GE 120V tank unit, a small Taco recirc pump (Model 006-B4 1/40 HP pump) and an aquastat to control the pump. We keep the tankless water heater set constant at 125 degrees, as well as the tank unit (so there is not a noticeable difference in water temperature when the 6 gallons in the tank has been used up). With the aquastat (senses temperature of the pipe immediately upstream of the pump) range of 95 to 120 degrees F, I notice the pump comes on about 3 times per day (I have not insulated the water heater or the piping yet - it is in my unfinished basement). We have seen no noticeable change in our electricity bills due to the addition of the water heater or pump. I see the tank as more of a thermal buffer than anything - considering that the combined volume of my 6 gallon tank and my 3/4" main hot water lines is about 9 gallons total (not a lot to have to reheat from around 95 to 125 about 3 times per day). And, as with all things in life - sometimes there is a small price we are willing to pay for the "luxury" of not waiting for hot water. Even better is paying that small price for the spouse to not have to wait for hot water.

Now, as far as CurlyDave's original question - it really has a lot to do with your local energy prices. If propane is reasonable cheap, it may be the best bet. If electricity is cheap (and you are willing to bit off the initial wiring costs and added service requirements - i.e. 400-amp main to the house), it may be a better way to go. When we built our house, I put in 400-amp service because I planned on adding exterior buildings and a shop down the road, and the PUD charged me an extra $1300 for "upgraded" service - claiming it was because the 400-amp service required a non-standard meter and extra terminations. Add to that the fact I had to run larger wire up my 700 foot driveway to the transformer (in two separate 3" conduits, no less), and larger wire into the house (in two more separate 3" conduits), and you can see how upgrading your electrical service can get costly. LP tank heaters have astounding efficiency ratings any more. They are also much easier to "plug-and-play" when/if they die. The design hasn't changed much in a long time, and probably won't any time soon. Tankless units may or may not be as easy to replace when they go out.

There certainly is an "up front" cost to tankless. With electric units, you are paying that cost through larger wire sizes, increased electrical service to the house, and high loads when the unit is running. With gas units, you are paying that cost through a high price for the unit (when compared to electric tankless), high cost for exhaust venting, and larger gas piping requirements. Add to that the "muddy" (at best) comparisons of efficiency between tank units (NG/LP/Electric) and tankless units (NG/LP/Electric) and it is really hard to tell what is truly "cheaper". There are simply too many variables to get a good answer - cost of each energy source, cost of installation, water usage habits (how much hot water do you really use, how often you use it, etc) - it really is different for each individual. If you are using a lot of hot water all at once and then don't use it again all day, you may be better off with a tank unit that has a slow recovery time - you simply drain down what water is in the tank when you use it, and give it all day to "recharge". If you use hot water all day in smaller doses, you may even be able to get by with one or several "strategically located" smaller tank units or a handful of "Point-of-Use" units and limit the amount of hot water piping installed in the house altogether.

One last thing to mention - I don't necessarily think that "endless hot water" will change your usage patterns. It's more of a comforting thought than a life-changing situation. In my last house, I had a 40-gallon gas tank unit. With my wife and I and two toddlers, we never ran out of hot water in normal use. I was up and showered and out the door at least an hour before anyone else in the house was up. My wife showered when she got a chance (stay-at-home mom). She used the water throughout the day for dishes, clothes, etc. At night, we would give the kids a bath, and maybe use some more hot water making dinner, doing the dishes, and some more laundry. Now, we have a bigger house, tankless (endless) hot water, and the kids are a few years older. But we still follow the same patterns, and the same usages more or less. About the only thing that has changed is now, I can start a load of wash, turn on the dishwasher, start washing the pots and pans, and my wife can run upstairs and run the bath for the kids without us worrying about running out of hot water somewhere in the middle of it all. I don't notice that we take longer showers, or spend more time using hot water than we did before. If anything, I think we use less water - especially since we have added the recirculation loop (don't have to run the water waiting for it to get hot) and all of our appliances are water efficient (dishwasher, front-load clothes washer). We don't pre-rinse our dishes much either before throwing them in the dishwasher, and our garbage disposal (yes, we have one, even though we are on a septic system) is ONLY for the stuff that inevitably ends up in the sink through food prep/cleanup.

That's my $0.02. As always, YMMV...

 

[LC Brewing]

Forgot to add this to the post:

My brother-in-law built his house about 12 months before I started mine. He installed an electric tankless unit in his, along with a recirc pump that cycles through the tankless heater (no external small tank like mine) based on a timer. He has been happy with it, says he doesn't notice the "cold water sandwich" effect except sometimes with the master bathroom shower.

But, he has also said that in his next house, he'd be inclined to go with gas rather than electric. He doesn't like the fact that he has 1/4 of his total electrical load "dedicated" to nothing but his water heater, and he feels like his electricity bill is higher than he'd like between the cost of heating the water and the cost of heating the house (he's got a forced-air heat-pump, which is fairly typical in this region due to our mild winters). Of course, if you're using gas, you've got to pay for that as well...

 

[Alan L.]

We don't have access to natural gas and LP is considerably more expensive, and we don't currently have a tank for that either. We are in the process of building a new home, and I have decided to go for a regular electric tank heater, one with something like R24 foam insulation in it.

I went to the Propane: Exceptional Energy: Welcome website and did a computation of LP tankless vs electric tank water heater. I plugged in $.13 for for electricity and $3 per gallon for LP (since I really don't know how much it is) and found the LP gas would actually cost more. Plus, you have the tank purchase or rental and the high initial cost of the tankless.

Add that to the fact that I don't really care to have open fires going in my house when I'm asleep, we have decided to stick with electric.

Besides, so it costs $50 a month to heat water, its just not that big a deal, and electric is just so much more convenient and safe.

Hank Hill almost convinced me to go propane, but not quite.

 

[kenmac]

Add that to the fact that I don't really care to have open fires going in my house when I'm asleep, we have decided to stick with electric.



Rinnai offers an outside wall mounted gas unit

Had a class on rinnai last week . They said that the new heaters will come with flush kits for all rinnai tankless heaters, to flush out the lime or hard water deposits that form on the inside of the water coils. Depends on the condition of the water in your area as to how many times that the unit will need flushing

 

[California]

It looks like the experts have gathered here to respond to Dave. While you are here, I have a question for this distinguished panel:

I'm thinking that both of the following locations would be less expensive to operate if they had on-demand heaters.

The ranch main house has a natural gas water heater outside, in a tin locker. There must be considerable heat loss with that weather exposure. (It has an insulation jacket).

We are only at the ranch about 30% of the time but I leave the water heater on continuous, because it is such a nuisance to get the enclosure open to adjust the control down at departure then up upon return, often in the dark.

There's a second gas water heater out in the barn for the washer. This is used by the rental cabin tenant, a single person, plus we run a couple of loads a month. I think that often, several days go by between uses of that water heater.

The third water heater is in the tiny rental cabin. I think the heat it throws off is helpful to drive down indoor humidity so reducing heat loss with a high-efficiency water heater would be pointless.

The three buildings are not close enough to share a water heater.

Would it be cost effective to install on-demand heaters in the first two locations? It seems to me it would be, but those of you who have used one might have some advice on other factors to consider. Any comments would be appreciated!

 

[_RaT_]

We don't have access to natural gas and LP is considerably more expensive, and we don't currently have a tank for that either. We are in the process of building a new home, and I have decided to go for a regular electric tank heater, one with something like R24 foam insulation in it.

I went to the Propane: Exceptional Energy: Welcome website and did a computation of LP tankless vs electric tank water heater. I plugged in $.13 for for electricity and $3 per gallon for LP (since I really don't know how much it is) and found the LP gas would actually cost more. Plus, you have the tank purchase or rental and the high initial cost of the tankless.

Add that to the fact that I don't really care to have open fires going in my house when I'm asleep, we have decided to stick with electric.

Besides, so it costs $50 a month to heat water, its just not that big a deal, and electric is just so much more convenient and safe.

Hank Hill almost convinced me to go propane, but not quite.

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

 

[Dargo]

I honestly don't know if electric water heaters have been vastly improved in the last 10 years or not. However, comparing even an old fashioned tank gas (either propane or NG) to the electric units I had for years, I see a huge difference in their performance. The electric units took twice as long to regenerate, cost a huge amount more to run, and I had to change the darn element every couple of years. Again, they may have been vastly improved in the last 10 years, but based on my past experience with them, you couldn't give me one. To say that they are an inefficient PIA would be putting it mildly.

 

[Tom_H]

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.

 

[BobRip]

It looks like the experts have gathered here to respond to Dave. While you are here, I have a question for this distinguished panel:

I'm thinking that both of the following locations would be less expensive to operate if they had on-demand heaters.

The ranch main house has a natural gas water heater outside, in a tin locker. There must be considerable heat loss with that weather exposure. (It has an insulation jacket).

We are only at the ranch about 30% of the time but I leave the water heater on continuous, because it is such a nuisance to get the enclosure open to adjust the control down at departure then up upon return, often in the dark.

There's a second gas water heater out in the barn for the washer. This is used by the rental cabin tenant, a single person, plus we run a couple of loads a month. I think that often, several days go by between uses of that water heater.

The third water heater is in the tiny rental cabin. I think the heat it throws off is helpful to drive down indoor humidity so reducing heat loss with a high-efficiency water heater would be pointless.

The three buildings are not close enough to share a water heater.

Would it be cost effective to install on-demand heaters in the first two locations? It seems to me it would be, but those of you who have used one might have some advice on other factors to consider. Any comments would be appreciated!

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.

 

[Doc_Bob]

. 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 wish I had installed a tankless system for just that reason.
Bob