Gas Tankless water heaters. Worth it?

[TomT]

The problem is that, here, gas is so cheap that the payback for solar water heating is almost forever... My average monthly gas bill year round for water heating, house heating, clothes drying, AND cooking is only about 22 bucks...

The OP also asked about combining the tankless water heater with solar. In fact this is a great combo. You install solar panels (the flat plate type is cheaper than the evacuated tube type) and a tank (you can reuse your old hot water tank if it is still in good condition). Then you pipe the hot water tank outlet into the tankless water heater. So you only pay for the temperature differential. During the summer you will likely use no additional energy at all to heat your water. The tankless heater can be gas or electric.

 

[smkettner]

How well does tankless work with low volume such as a recirculating pump?

 

[davewill]

How well does tankless work with low volume such as a recirculating pump?

I put one in to replace a tank with recirculating pump. You can't use the same low volume recirc pump with a tankless system. The pump was replaced with one that was triggered by buttons placed in the kitchen and bathrooms. You press the button and the pump runs until the hot water loop reaches temp. It takes about 30s.

 

[TomT]

I have the same type of recirc system with wireless buttons in the baths and kitchen. It works well.

How well does tankless work with low volume such as a recirculating pump?

I put one in to replace a tank with recirculating pump. You can't use the same low volume recirc pump with a tankless system. The pump was replaced with one that was triggered by buttons placed in the kitchen and bathrooms. You press the button and the pump runs until the hot water loop reaches temp. It takes about 30s.

 

[solartim]

Our tank is part of our emergency water storage. It's 3 months old now, I spent a little extra and got one with the sacrificial anode, hope it will last longer, but the old one went for 12 years. I replaced it with the same capacity, but the size was much bigger because of built in insulation, felt silly putting the old heater blanket on it, but hey, every bit helps.

 

[rickrides]

I was going to install an electric tankless to use the excessive power from my solar system until I found out it takes three 40amp circuits. My house only has 100amp service so I bought a Leaf to use my excess power.

I like that hybrid AO Smith water heater but it takes too much floor space.

-Rick

 

[walterbays]

I have the same type of recirc system with wireless buttons in the baths and kitchen. It works well.

Me too.

The buttons are necessary rather than using thermal control of the recirculating pump because, since it is more powerful and noisier than a regular pump. Also, this way we only heat water when we need it. The tankless heater did make me realize how inefficiently most houses are designed with the water heater in the far corner and long pipe runs. When we had a tank water heater we'd get hot water faster even with the recirculating pump turned off. Just from thermal convection through the recirculating pipes enough hot water kept moving to keep the pipes warm. Of course what that meant was not only were we burning gas to keep the tank water hot, we were also burning gas to keep the pipes warm. We probably used more gas in these ways than in actually heating hot water we used, and that is the biggest reason for the big energy saving from the tankless heater. (It's analogous to all the gasoline I used to burn in my Prius just to heat the ICE up to operating temperature on short trips.) Now we burn nothing until we need hot water, but we have to push the button 30 seconds or so before we open the tap.

 

[klapauzius]

I installed one 4 years ago and it saves on average $150 per year vs
the tank heater we had before.

If you have to install a new one anyway, depending on the installation cost, I think
you can break even anywhere between 6-10 years.

Independent of cost, it is nice to have
a) endless hot water
b) no tanks that can leak

Solar heaters seem to be excessively expensive for what they do, and financially dont
make any sense, not even with incentives.

 

[lukati]

The problem is that, here, gas is so cheap that the payback for solar water heating is almost forever... My average monthly gas bill year round for water heating, house heating, clothes drying, AND cooking is only about 22 bucks...

The OP also asked about combining the tankless water heater with solar. In fact this is a great combo. You install solar panels (the flat plate type is cheaper than the evacuated tube type) and a tank (you can reuse your old hot water tank if it is still in good condition). Then you pipe the hot water tank outlet into the tankless water heater. So you only pay for the temperature differential. During the summer you will likely use no additional energy at all to heat your water. The tankless heater can be gas or electric.

That is indeed very cheap. Consider yourself lucky. However, even in your situation a home built solar system will pay for itself fairly quickly.
More information here: http://www.builditsolar.com/Projects/WaterHeating/water_heating.htm" onclick="window.open(this.href);return false;

I built a solar air heater a few months ago. It is really fun and quite easy to do.

 

[arnolddeleon]

How well does tankless work with low volume such as a recirculating pump?

I have a tankless with a recirc pump. Works great!

The other benefit of the tankless in my case is the extra space I got back in my garage.

I had it it plumbed so I could add solar in the future but I would probably send that money on more photovoltaic panels.

arnold

 

[HarryHouck]

Thanks for the comments. I flushed out the scale and will look for a hybrid heater, AO Smith or Reliant brand. The true tankless require a 3/4" dedicated gas line. I was quoted $3,200 to have one installed. A hybrid uses a 25 gallon tank, doesn't require a dedicated gas line and uses the same vent as the 40 gallon heater.

 

[keydiver]

The heating is so fast, i doubt a solar water heater will make a difference. If cost is no option, obviously a solar water heater helps, but the cost of them is so expensive it takes usually about 15-20 years to get your cost back.

This is very wrong. Especially with all the Federal, State, and local/utility rebates, a solar hot water heater has one of the fastest paybacks. And, as someone else just posted, if you use the solar to preheat, it makes a great match with an insta-hot type hot water heater, just make sure you get the kind that are compatible with solar. They check the incoming water temperature, and only heat it as much as necessary, instead of turning full-ON as many do. By themselves, electric tankless hot water heaters only save 10-20% over a standard electric hot water heater.

 

[lukati]

The heating is so fast, i doubt a solar water heater will make a difference. If cost is no option, obviously a solar water heater helps, but the cost of them is so expensive it takes usually about 15-20 years to get your cost back.

This is very wrong. Especially with all the Federal, State, and local/utility rebates, a solar hot water heater has one of the fastest paybacks. And, as someone else just posted, if you use the solar to preheat, it makes a great match with an insta-hot type hot water heater, just make sure you get the kind that are compatible with solar. They check the incoming water temperature, and only heat it as much as necessary, instead of turning full-ON as many do. By themselves, electric tankless hot water heaters only save 10-20% over a standard electric hot water heater.

Thanks for the support! I find it ironic that on a forum with exceptionally high PV ownership we would have to argue the financial benefits of solar thermal. I always thought it was common knowledge that solar thermal had a faster payback than solar electric (plus a much higher energetic harvest).

 

[arnolddeleon]

The heating is so fast, i doubt a solar water heater will make a difference. If cost is no option, obviously a solar water heater helps, but the cost of them is so expensive it takes usually about 15-20 years to get your cost back.

This is very wrong. Especially with all the Federal, State, and local/utility rebates, a solar hot water heater has one of the fastest paybacks. And, as someone else just posted, if you use the solar to preheat, it makes a great match with an insta-hot type hot water heater, just make sure you get the kind that are compatible with solar. They check the incoming water temperature, and only heat it as much as necessary, instead of turning full-ON as many do. By themselves, electric tankless hot water heaters only save 10-20% over a standard electric hot water heater.

Thanks for the support! I find it ironic that on a forum with exceptionally high PV ownership we would have to argue the financial benefits of solar thermal. I always thought it was common knowledge that solar thermal had a faster payback than solar electric (plus a much higher energetic harvest).

Hmm, not necessarily. Grid tied PV always almost always has a place to put the energy it captures (sell it to the grid). While solar thermal captures more of the energy that is falling on it at some point if there is not enough demand (someone using the hot water) it will have to "throw away" the extra energy. In my case my gas bill pretty much never exceeds $40/month, last year my entire gas bill was less than $265. I have tankless gas water heater, gas stove and gas dryer. My primary heat source is an air source heat pump which is backed up by a gas furnace. I had looked into a solar hot water installation and it was going to run me around at least $4500 (incentives factored in few years ago). So best case scenario if my entire gas bill was attributed to hot water production I would need 17 years to recoup my cost but more likely it would be over 20 years as Pipcecil wrote. N.B. There are plenty of other cases where solar thermal makes sense just not always. There also many cases where grid tied PV is cash flow positive on day one, savings on day one exceed the cost (lease, finance or the opportunity cost of the money).

 

[lukati]

Hmm, not necessarily. Grid tied PV always almost always has a place to put the energy it captures (sell it to the grid). While solar thermal captures more of the energy that is falling on it at some point if there is not enough demand (someone using the hot water) it will have to "throw away" the extra energy. In my case my gas bill pretty much never exceeds $40/month, last year my entire gas bill was less than $265. I have tankless gas water heater, gas stove and gas dryer. My primary heat source is an air source heat pump which is backed up by a gas furnace. I had looked into a solar hot water installation and it was going to run me around at least $4500 (incentives factored in few years ago). So best case scenario if my entire gas bill was attributed to hot water production I would need 17 years to recoup my cost but more likely it would be over 20 years as Pipcecil wrote. N.B. There are plenty of other cases where solar thermal makes sense just not always. There also many cases where grid tied PV is cash flow positive on day one, savings on day one exceed the cost (lease, finance or the opportunity cost of the money).

You argue payback time for solar thermal and cash flow for PV. We need to compare apples to apples.
Let us assume your $4500 solar thermal system was designed to provide ~75% of your yearly hot water needs, a reasonable design target, and let us assume that this would save you $175 per year (~3.9%). Depending on the interest you pay, that could easily be a cash flow positive investment. On the other hand, according to Solar Today, the current installed cost per watt PV is ~$6.80. At a good location in Southern California an installed watt yields about 1.5 kWh per year. Electricity rates can vary greatly, but at $0.10/kWh the return would be 15 cents per year per watt installed (~2.2%). Incentives and preferential rates for solar of course change the equation, but the payback time is still quite long in most cases.
My attitude is we should try to harness as many solar watts as possible and even if the financial calculus doesn't quite add up, the CO2 not emitted more than make up the difference.

 

[keydiver]

I think part of the confusion is that I was comparing it to a standard electric hot water heater, a little off topic,sorry. A typical electric hot water heater uses $500+ per year in electricity, so the payback for solar hot water is very short.

 

[detlefo]

We've had one for around 5 years and it is great. DO NOT GET ONE IF YOU HAVE TEENAGERS IN THE HOUSE. THEY WILL NEVER GET OUT OF THE SHOWER! :lol:

 

[Yanquetino]

I had used tankless water heaters when I lived in South America, and thought they were great, much better idea than the "boilers" I had grown up with here is the States. Consequently, nearly two decades ago, I installed an Aquastar tankless water heater in the home where we lived in the mountains.

That model has worked flawlessly ever since, and MORE than paid for itself with the savings on our gas bills. We now rent out that house to skiers, and I think that they appreciate being able to shower one after the other, then do laundry, then run the dishwasher, then fill the jacuzzi, yet never run out of hot water. The only drawback is that, up there in the mountains, the incoming water is only about 40° in the winter, and thus you have to turn on only the hot water to enjoy a steamy hot shower. In the summer, however, it can scald you if you're not careful.

We built a new home last year, and I insisted on getting another tankless water heater, this time a Rinnai. This model has an even greater capacity, able to raise the temperature higher, and still supply more than one shower or appliance at the same time. Of course, the incoming water is not as cold in this desert as up in the mountains, so that helps. Still, I don't think I would EVER go back to a water heater with a tank again. This was one of the best decisions I have ever made. Along with my solar panels, and reserving my Leaf, of course.

 

[LTLFTcomposite]

We've had one for around 5 years and it is great. DO NOT GET ONE IF YOU HAVE TEENAGERS IN THE HOUSE. THEY WILL NEVER GET OUT OF THE SHOWER! :lol:

+1

I turned the thermostat down on our conventional water heater specifically so it will run out faster. Of course this works OK for me because they never get up before I do.

 

[EVDRIVER]

Anything electric for primary hot water is an energy pig. I had a gas water heater and went to gas tankless and never looked back and I saved quite a bit on energy. Why would one assume thermal solar heat is wasted? I gets stored in a tank. I am also going to switch from forced air to radiant floor heating which is far superior and I would really like to have thermal solar in conjunction. High efficiency on-demand can be vented with plastic and one can put them at local sources at times for even more gains. A friend of mine has solar electric and stupidly installed electric on-demand water heaters, once he changed them to gas he saved about $500 a month because of the kids.