LPG Tankless vs. Electric Water Heater

[CurlyDave]

After reading the thread on "Tankless water heater code question", I have a completely different question.

Which is going to be lower cost to operate, electric tank-type, LPG tank-type, or LPG tankless. We are building new, and can have it installed any way we want for minimal cost.

Advantages and disadvantages of either type?

The only issue is that Natural Gas is not available.

 

[gsganzer]

CurleyDave,
I would have to think that the LPG tankless would be cheaper to operate. The problem is that you also have to overcome the initial cost.

If you look at the energy ratings of an Electric tank and an LPG tank, the LPG lists lower operating dollars per year. The tankless is supposed to improve on that efficiency by only heating the water on demand, not cycling on/off to keep 40-50 gallons hot.

I think the real benefit of the tankless is that you have a never ending supply of hot water. One of the drawbacks I've heard is that it takes slightly longer to get hot water to the tap because you don't have hot water "at the ready". On one of the schematics that was posted on the "water heater code post", they show a small 5 gallon tank installed in the "tankless" system and a return circuit, so you always have hot water ready. That arrangment would nip a little from the total "efficiency" rating of a tankless, but I think it looks like the best of both worlds.

 

[_RaT_]

After reading the thread on "Tankless water heater code question", I have a completely different question.

Which is going to be lower cost to operate, electric tank-type, LPG tank-type, or LPG tankless. We are building new, and can have it installed any way we want for minimal cost.

Advantages and disadvantages of either type?

The only issue is that Natural Gas is not available.

The answer may also depend on what you pay for electricity. Remember, in many cases now, its not just the cost per KWH but also the distribution and transmission of the electricity you need to consider when determining the true cost of electical power. They do make tankless electrical units that have huge heaters, something in the ballpark of 70 amp 240V. The cost of the wire alone would be significant. I would add that the schematics that show the Rinnai tankless using closed circulation loops will kill efficiency more then one is led to believe. In the long runs of 3/4" copper even with great insulation, the small 120V electric heater will recharge the hot water supply a considerable number of times. I would much prefer the Metlund system for obtaining fast hot water. Here is the link, I have installed 3 of these on tank systems. For tankless, I am told you need the larger pump to trigger the flow sensor on the tankless heater. Advanced Conservation Technologies: D'MAND Hot Water Systems.

 

[Dargo]

RaT brings up about the only drawback I have found in the last couple of years of tankless heaters, and that is that they require about 1 gallon per minute of demand to kick on. If you use one of the front loading, low water volume, washing machines you may have an issue. I only have one 70 gallon tank water heater left and all the rest are tankless. Our washing machine in the main house is operated off of the old 70 gallon tank heater. In our pool house, the washing machine is operated off of the Rinnai tankless without any problems. However, the washing machine in the pool house is the standard top loading model.

There are several 'work arounds' to the potential problem with the low water washing machines, but right now I'm not concerned since I still have a tank unit on it. When the time comes to replace that tank unit, I will go tankless though. Being the penny pincher, scrouge, tight wad, etc. that I am, I definitely noticed a drop in our average utility bills for any given month since going tankless on two of the water heaters. Now, I do have a large family, but for most every month it sure looks like I'm saving about $25 to $30 per month on my natural gas part of my utility bill when comparing to the same month of the year back when I used all tank water heaters.

Supposedly the electric tankless water heaters are over 99% efficient. The natural gas fired ones are what I have, and I can't recall what they are rated on efficiency. The reason I didn't go with the electric models was due to the fact that the size tankless water heaters I installed would have required 100 amp service for the smaller residential unit, and 125 amps for the larger commercial unit. Uh, I didn't have enough juice at hand to make them work without major re-wiring, so natural gas it was for me. A friend who just built his house last fall went with 2 electric tankless units when his house was built, and he absolutely loves them. You'd think he is a salesman for Rinnai the way he goes on and on about them. I have no experience with propane, but I'd assume that they would be similar to NG.

I hope that helps. It sure did make things better in the mornings when we have seven people all taking showers and getting ready to leave all at the same time. It really did cure the cold shower issue for the last person in the shower. Good luck with whatever you opt to buy!

 

[Tom_H]

Last Oct. I got a Takagi LPG, the more advanced model for about $1100. It has 4 separate burners and each is variable. Hot H2O never runs out. We got the remote control thermostat (it mounts on the wall and is connected by hard wiring, therefore you can't carry it around like the TV remote) for about an extra $100 and it's been worth it. We placed the thermostat inside by the master bathtub. It ranges from 99 to 167 degrees. I set it at 99 when I shower and can still turn the faucet past the center to the cold side to get very lukewarm water. When we want to wash towels in hot H2O, it's very easy to kick the temp. up to 167. Also, if the water in the tub gets cold and you want a small amount of super hot water to bring the temp. back up, we can just reach over and adjust the thermostat. We normally put it at 115.

The only downside is that it won't kick on if you want a mear drizzle of hot H2O. If I'm rinsing dishes in the kitchen sink, I have to have the flow at substantially higher than a drizzle for the burners to come on, but I can still run it at well below full blast.

The up sides are endless hot water, easy temp. control, potential for high volume flow, all with substantial heat (this model will supply up to 4 showers simultaneously), and energy isn't wasted keeping water hot and on standby for 99% of the day. Also, though the price of the unit is higher than a tank, the life expectancy is far longer so that the pro rated cost is reasonable.

Previously we had a gigantic heat pump with thermal reservoir for Heat, hot water, and AC. When the unit (outside) went, kaput, I didn't want to replumb to put this unit inside. With the old unit gone, there was already a 3.5' x 8' concrete slab and all plumbing in place. I bought some flat and angled aluminum, stainless steel nuts, bolts, and expansion anchors, and built my own frame to mount this thing alongside the new regular sized heat pump/ac on the old concrete pad. The contractor had an exterior cap he put on top where the exhaust normally enters a vent pipe. It has worked just fine, even in driving rainstorms.

I wasn't familiar with the Takagi brand, but it's stats are better than the more well known names, and we haven't had a single problem of any kind. If I build another house, I'll definitely install this.

 

[ultrarunner]

Hi Dave and Tom

I think the availability and cost of Natural Gas, LPG and Electricity in your area will be the determining factor. The one luxury of a properly sized tank-less unit is "Never running out of hot water" and this can be a bad thing with teenagers!

In Austria, I installed a Siemens Electric Tank-less unit (380volts 3phase) that has been satisfactory. All the comfort of home without the yearly property tax of a tank type water heater or the need for a separate "Boiler" room.

In Europe, you are assessed a water heater property tax each year based on the size of your tank... no tank, i.e. tank-less... means NO yearly water heater tax.

The reason I said satisfactory is because it does take 3 times longer to draw a bath due to reduced water flow. Washing machines are not a problem because virtually all European Washing machines have their own self contained heating element which will heat the water to as high as 180-190 F if selected for whites and linens.

I've never had a standard American tank type gas water heater "Cycle" when up to temp. I keep mine set about 115 for safety and economy.

25 years ago, I installed a 30 gallon propane water heater in a cabin at Tahoe. The heat of the pilot light is enough to keep the tank water hot, well at least warm enough for showers. I always turned the selector to "Pilot" when leaving for an extended time and I would always find the water "Hot" when I returned, even in winter when the inside cabin temp of 35 degrees.

On a side note, the Europeans I know are always amazed how inexpensive construction materials are in the States. Several years ago, I took my Uncle, a builder by trade in Austria, to my local Home Depot. One of the things he commented about is that everyone in America could afford a 150 liter (40 gallon) gas water heater when he saw the $124 price! (I know they now cost double with the new design... but that's another subject) He said everyone would have a tank type heater if they could afford it.

In Europe they also have two electric meters when you heat with electricity. The "Night" electric meter bills at about half the rate of the "Day" meter and electric tank water heaters have a built in timer to take advantage of the cheaper night rates and not heat during the day.

 

[BobRip]

You might consider a better insulated tank type heater. I purchased a Marathon brand hot water heater about 3 months ago. We see about a $10 per month drop in cost. I also added a front loader washer just prior to that, so some of the savings is probably from that. The Marathon heater has 2.5 inches of foam insulation and a lifetime warranty on the tank. I got tired of replacing tanks every ten years or so. I am very against the electric tankless. If you plan to use more than one faucet at a time the electrical power requirements are huge. Also there is no way you could run it off a typical house generator. Just some things to think about.

 

[CurlyDave]

Well, now I have a lot more to think about.

We do have the low-flow type washer, and if it won't trigger a tankless unit that is going to be a problem. I understand the work-around, but a small electric tank for the washer, and then a small electric tank for the kitchen, and one for our bathroom, and then one for the guest bath, and I bet a lot of the tankless efficiency is gone.

Then there is the other issue I haven't seen addressed. What does endless hot water do for our septic field? Do I really want to encourage more water consumption?

Most of the time it will be just the two of us. Maybe an electric tank-type with lots of wrap-around insulation is a better answer. Nothing reminds a guest to limit their water consumption to save the septic field more than running out of hot water...

 

[_RaT_]

Then there is the other issue I haven't seen addressed. What does endless hot water do for our septic field? Do I really want to encourage more water consumption?

The Metlund pump eliminates dumping water. You can even install it on a system that does not have the closed loop heating circuit. Pull water through the hot line and push it into the cold. Pretty simple. Its wireless as well and you can have as many remotes as you desire.

I know folks rave about tankless, but I have yet to see one that can handle two devices at once without a noticeable reduction in flow. Perhaps the one Tom H has is the ticket, the Takagi. I have had Bosch and now Rinnai model 2424, its a little older so maybe they have improved. I did not see a noticeable decrease in my gas bill going tankless but then, my gas bill is always quite low anyway.

 

[Tom_H]

I saw these type units in Europe decades ago. They have improved a lot since then. I have used Bosh and others in various places, and some really have flow and/or temp. drops when you use 2 applications at a time. With the Takagi, we have run 2 showers, dishwasher, and clothes washer simultaneously with no problem. Put more demand on it and it just kicks in another burner, up to four.

Our washing machine fills very very slowly, but the flow rate is enough to keep the burner on if we are using hot water. When we do wash in hot water, I kick the thermostat to 167, turn on the garage utility sink faucet to hot. This sink is close to the clothes washer, so this way I get hot water in the line and very close to the washer. After the hot water reaches the utility sink, I turn on the washer and cold water flows in for only a few moments before the hot courses through the line and reaches the drum. After the hot water has started entering the washer, I turn off the utility faucet and the rather low flow into the washer is enough to keep the water heater going. The unit would come on without doing the utility faucet; I just do this so there'll be less cold water accumulating in the drum before the hot water gets there.

Again, I knew about Bosch and other well known names, and was initially dubious about Takagi, which I had never heard of. I was afraid the contractor was recommending it because he got good markup on it. After reading stats and a few online reviews, I went for it and it has exceeded my expectations.

Edit/update: Dave, I had those same fears of needing to place those little tankless electric units at all the lavatory faucets, but I haven't needed to. Though it won't stay on at a "drizzle" it will stay on at a low flow. Having the thermostat in the master bath has been an advantage because there is a small LED indicator that illuminates when the unit is burning and goes off if it's not. I can crank the flow down until I hit the threshold, and if it goes off, I know immediately and can notch it up a tiny bit and it's back on. This way, ther's no guessing.

BTW: the prices I gave were for the heater installed, but cost only on the thermostat. I installed the thermostat myself.