Solar hot water vs. tankless systems

kntryhumanJanuary 19, 2009

I live in southern Louisiana. We're renovating a very old house, using spray foam insulation in the outer walls, roof and under the house.

We had a solar company come out over the weekend. With rebates from the state and Fed's, we would have to pay $2000 for an 80 gallon solar water heater. About the same price as a tankless heater.

What are the pros and cons or each?

Thank you for reporting this comment. Undo

In hot climates, a heat recovery unit on the A/C beats solar hands down. Less expensive, delivers much more hot water, and improves A/C efficiency. Most hot water usage in homes occurs in the early morning and evening when sunlight is not available to reheat the tank. An HRU provides heat at those times, preventing the back-up heat element from switching on and negating your energy savings. My feeling is that Solar in hot climates is a great disservice to those wishing to save energy since HRUs do the job so much better and cheaper.

I have serious concerns about spray foam on the underside of roof decks. I have yet to see a foam that allows water to pass through. Eventually all roofs develop leaks. When that occurs, with the foam, you'll not see the leak and the water will spread between the foam and decking, rotting the plywood and the truss members without any indication it's happening. I believe this is going to be a time bomb that will not be noticed for some time and require code to specify more durable roofing underlayment (possibly the use of 'ice dam' underlayment on the full roof).

My complete energy rant....

Currently the U.S. is sending an exorbitant portion of it's energy money overseas. Anyone who does not take some initiative to cut their power bill (and therefore energy usage) needs to realize that they are providing 'aide and comfort' to those who would love to see us dead and are taking great delight in our current difficulty. Drilling for more domestic oil is not the panacea for this mess as prices are not being controlled by the mechanism of supply and demand, rather by a combination of speculators and OPEC who control such a large portion of the world's oil supply that they can easily negate any of our drilling efforts by simply closing the tap at their end just a little. Any oil we produce won't save us any money. We currently produce a large amount of oil in Alaska but do you see us getting a break on it because it's domestic? No, we pay the going world rate, set by the aforementioned OPEC and speculators...and provide another windfall for the oil companies. They sit before Congress smiling saying their huge profits are necessary to allow them to explore....excuse me....we are talking about NET PROFITS here...what's left AFTER exploration expenses. We the people have no control over this sort of manipulation of our government, whether we have Republicans or Democrats in charge. . .there's too much money involved. Our only hope is to cut energy usage, not drill and give them more avenues for profit. We all need to realize the best thing we can all do to help the energy situation and economy is to take individual action. Rather than waiting around for the government to do something we can each cut our electric usage dramatically....up to one half of your bill if you are willing to spend a little time and money. Every time you see your power bill shrinking, that's money for you rather than some oil producer. Money you can spend here to help the economy or save as you prefer. Here are several sites worth visiting that aren't selling anything but tell it like it is. Plenty of simple and painless techniques to cut your power bill.

Mr. 'Bluejay' does a great job explaing away a lot of scams...see his section on surge suppressors for example.

Be sure to look at the 'Half' program.

The current situation has people grasping at all sorts of non-cost effective solutions that sound great on paper but don't hold up to scrutiny in the real world. Solar electricity is one of those as would be wind power in cent. Florida. Solar PV (photo voltaic) just costs too much at the present. Hopefully ongoing research will change that in the future but it's not ready for prime time yet. The rental program below will probably be practical if it gets underway.

Check out this site for info on a possible contender for solar PV at home.

The 'Build it Solar' site also has some good info about costs.

Plenty of outright scams getting too much press also. The 'run your car on water' crowd is one I can think of (apparently many people didn't pay attention in high school physics). A good site explaining the physics that negates that scheme is here along with other interesting info about some of those behind the current revival.

Another scam that's been revived is the 'phase controller' that supposedly saves electricity by making motors run more efficiently. Home show demonstrations with an electric motor show it's electricity usage dropping dramatically when the motor is plugged into the device rather than straight into the incoming power. These devices actually do work in the applications they are designed for...this has the unfortunate effect of helping the scammers (or to give them the benefit of the doubt, uneducated-in-electricity folk) sell these things. An industrial application that produces savings would be a big table saw in a woodworking shop that runs constantly. When it's not cutting wood, the motor is under no load and at that moment, a phase controller will save energy. The goal of electrical engineers is to make sure anything with a motor runs that motor at rated capacity at all times...that's the point a motor is most efficient. Their striving for this is what has made ACs and refrigerators much more efficient lately. The point here is motors in your home all run at rated load all the time. There is no 'off load' time like with the big table saw. A 'phase controller' saves nothing in this situation.

In hot climates a proven strategy that works well is a heat recovery unit attached to your AC unit. It provides free hot water and also increases the efficiency of the AC a couple of SEER points by reducing head pressure (and electricity draw) on the compressor. You're paying for your A/C to move a great deal of heat out of your house, you might as well use that heat to provide you with hot water. Adding one of these to an older AC unit that still runs well is a good way to cut $30-$50 off your monthly power bill during AC season (which here in cent Fl can be about 9 months). The neatest thing about this solution is that it's cost-negative. In addition to being free hot water as opposed to other 'high efficiency' heaters that still consume energy, it actually lowers your cost of air conditioning. Here is a manufacturer's site for two of these and a power company document about it as well. The second mfg site has a neat calculator for your savings...but my experience shows it to be somewhat under-optimistic. I don't think it's taking into account how a hru will improve your AC's efficiency. There are claims that they don't work with higher efficiency unit, but I have two HRU connected to 13 SEER heat pumps that provide plenty of hot water.

Another real saver in hot areas is a radiant barrier in the attic or metal roof. Both create similar savings. If you are re-roofing, consider changing to a metal roof. When installed over a normal wood-decked roof, noise is not a problem. Most people thinking of a noisy metal roof have heard one that's been installed over wood 'stringers' as was the case many years ago...very noisy in a rainstorm. If you have a hip roof house or a lot of dormers metal may be too costly due to the waste from all the cutting to fit...metal is most cost effective on a two-slope 'shed type' roof. Radiant barriers can either be installed during easy way is using foil-backed plywood roof decking ...or added later. See this site for info and material.

Tankless water heating is also a problem area for accurate claims of savings. A gas tankless heater can be much more efficient since it eliminates the flue that passes through the center of a conventional tank heater and becomes a chimney to carry away your water's heat once the flame shuts off. Electrics are another story... Big savings are claimed that are not supported by data. No studies are shown that give specifics telling you what make/model/year tank unit is being compared with the advertised tankless. Maybe they use an ancient cast iron tank heater insulated with sawdust? Verifiable details please. Somehow electric tankless heaters dodge the requirement for the yellow government 'EnerGuide' label that every other appliance must have. If they had to carry it, their claims would show to be false. Claims of better durability because of 'no tank' are a red herring also...the 'tank' still exists, only it's now smaller. Buildup from hard water deposits may be more of an issue with tankless, possible surcharges from the power company later due to high instantaneous current draw, heavy wiring needed, new construction with planned tankless can make retrofit of tank type later very difficult due to lack of dedicated hot water piping, incompatibility with future solar or other alternative power sources due to aforementioned high current draw. These are all serious disadvantages of the tankless electric. All electric hot water heaters are 100% efficient at heating water. That's a function of an electric element immersed in water. The only added efficiency of a tankless is the reduction of standby losses which are very minimal in new technology insulated tank heaters. Put your hand on one and you'll see they pretty much run at room temperature...very little standby loss.

Another myth is that shading a A/C condenser saves '10-20% or more. The reality is not much. Similar situation to a garden hose left out in the turn on the water and what comes out is scalding hot....but in a few moments the water is cool...sun impinging on something will make it very hot but that is a function of 'accumulated heat'. What heat is striking something and being carried away by a fan is very small. See the following link about this subject...

A free, online calculator that can help you plan upgrades is here:

Two technologies have the potential to really turn things around..see these two links for something both companies say will arrive sometime next year...Still better to get moving with your own plan that to wait with your fingers crossed..

Please use due diligence when deciding on ways to save energy. There are LOTS of scams out there. The internet is a great source of info and you can easily see both points of view on any energy saving strategy. Just simple conservation by time-tested means is still the best way to approach our dilemma. If we all cut our power bill in half, we'd all have much more money in our pocket and our nation would be much more secure. This action, along with Mr. Picken's ideas on wind power, WILL free us from imported oil and rather quickly.

    Bookmark   January 20, 2009 at 3:39AM
Thank you for reporting this comment. Undo

Last year I weighed the costs and benefits of a solar thermosiphon system versus a tankless, to replace a gas tank version. I went with solar. But because of our usage patterns the electrical backup heater has to kick in fairly often in high demand times or during storms. The overall impact has been to raise my energy bill significantly, and give me less hot water.

Now I'm considering the addition of a gas-fired tankless backup to work in conjunction with the solar system. If I had the room I'd even go back to a gas-fired tank.

There is no question that a tankless unit would have been better for me.

    Bookmark   February 9, 2009 at 6:32PM
Thank you for reporting this comment. Undo

What makes this happen? I certainly don't want to have a higher electric bill.

Our state offers a 50% rebate/refund and the Feds have 30% credit so the solar hot water will end up costing me $2000. This is about the same for the tankless heaters that I have to pay to use.

    Bookmark   February 9, 2009 at 7:20PM
Thank you for reporting this comment. Undo

Out here in southern California the cost of electricity is higher than the cost of gas. Since electricity has a tiered pricing system to encourage conservation, my extra consumption was charged at a much higher rate than normal. So I'm saving $20 in gas per month but spending an extra $100 in electricty -- I kid you not. Live and learn.

Again, this is due in my case from going from a gas tank system to a solar system with an electrical backup. Some of my problems may have been solved by going with a larger solar tank to get through my periods of high demand, but I can't be sure.

If you get a solar system, make sure they install it with a whole house thermostatic mixing valve. My contractor did not, which I've only now discovered as I'm looking into adding the tankless to receive the pre-heated water.

    Bookmark   February 9, 2009 at 8:03PM
Thank you for reporting this comment. Undo

Thanks for the information.

I'm still trying to decide which would be better for us. We're not home all day but at night, our grown sons empty a 50 gallon water heater each.

    Bookmark   February 9, 2009 at 8:27PM
Thank you for reporting this comment. Undo

For that kind of demand a tankless sounds best for you unless your solar storage unit was huge. Solar is a bit better if you're using the water during the day, so it recharges. But if you have peak demand in the morning and night, it isn't as efficient.

    Bookmark   February 9, 2009 at 9:00PM
Thank you for reporting this comment. Undo

That's the kind of information I'm looking for. Thank you.

The unit they're talking about putting in is 80 gallons.

The tankless won't take up 3'x3' either.

    Bookmark   February 9, 2009 at 9:28PM
Thank you for reporting this comment. Undo

You might want to look into whether they offer a gas backup heater to the solar, rather than electric. Of course it depends on the local relative cost of energy.

And the reason you should insist on a whole house thermostatic mixing valve is so that you can have extremely high temp water in the storage tank (prevent legionella), but before it enters the house it is mixed with an adjustable amount of cooler water. It will reduce the risk of scalding (solar hot water can reach 160 degrees if not more in the summer), but also it will mean that your 80 gallons of hot water will go further since it is being mixed closer to the tank. Personally I would set the mixing valve at around 110.

If you go straight tankless then I don't think the mixing valve is necessary.

Let us know what you end up with and how it works!

    Bookmark   February 9, 2009 at 10:17PM
Thank you for reporting this comment. Undo

I will be sure to let you know.

We won't be installing either for a few months. The house is still gutted right now.

Thanks again for the information.

    Bookmark   February 9, 2009 at 10:37PM
Thank you for reporting this comment. Undo

Thanks, Gary.

The system is going to cost $8400 up front but with our state offering 50% and the Fed 30% tax credits, it will only cost us $2000 out of pocket.

I'm still doing research so thanks for the link.

    Bookmark   February 10, 2009 at 8:17AM
Thank you for reporting this comment. Undo

Tankless heaters are very expensive. In addition, you need big gas pipes or electrical conductors since a lot of energy is needed all at once. If it were not for the huge market distortion of the LA tax credit, I would not even be thinking of solar. In spite of it, I may go to a heat pump water heater.

I almost always need dehumidification in South Louisiana. Electricity is cheap here. A HRU might be nice, but I doubt may AC techs know how to install them and the ones that do will charge a lot for it. A HPWH can be an easy DIY so that makes up for the lower value from a HPWH.

The solar will probably last longer than the HPWH and can provide hot water in the event of a power outage. It is becoming a difficult choice.

    Bookmark   April 16, 2010 at 8:20PM
Thank you for reporting this comment. Undo

I have been doing research on both and have found issues related to both.

Tankless systems - the main pro and the real reason why Europe has the majority of these systems are because of size constraints of homes.

You are still PAYING to heat the water!! and the way it works to heat a small area of pipe to a high temp so that by the time the water passes through it it is hot.

For electric - look at the running amps of those things and if you do use a lot of hot water you will see little to no savings.
Other issue is that there is a minimum water flow before they kick on and if you are taking a shower at medium temperature where cold and hot mix sometimes the hot will never kick in. Add in a variable problem that your plumbing has a long way to go to get to your shower. You can be taking a shower and the water goes completely cold. Then you turn it up and the hot kicks in too hot.

Gas is a more efficient way to go, but then you have the issues that come gas.

A Properly sized and installed Solar system should provide you with most of your hot water needs. In essence the solar collector should be your main heating element and if you want to always have hot water,and not change any normal routines than a backup element will be required.

Also if you are concerned about not getting enough solar heat gain in Louisiana than make sure you have an efficient backup heater and your electric bills will be fine.

    Bookmark   July 27, 2010 at 10:07PM
Thank you for reporting this comment. Undo
Jean Bo

My father an architect, designed and built his dream home back in 76, he was very forward thinking and meticulous in his planning. He installed a solar hot water heater at time of construction. I can tell you from.... How many years experience? 34 years of use, and they still own the house that it works flawlessly. The water is crazy crazy hot. So hot that if little kids were in the house you would have to work on a way to control that. With a very large tank holding your hot water sorry wish I knew the number here but it's a big one, there is always plenty. On the rare occasion that we have 3-4 days of clouds/ rain you would then flip on the booster. This has rarely been used. Always sunny in south Fla. After the few hurricanes we have been through and lost power for sometimes weeks! How nice to take a hot shower, run the dishwashers (with a generator tied in of course)and have hot water to do so. About 10 years ago I guess the panel was replaced with a new one (they replace things before they break and fail) and had a new custom stainless steel tank installed sorry don't know the particulars on that. Again it has been flawless and is the one thing in the house that doesn't require any maintenance. BTW I have been hearing from people that they have a pump with their solar system. We don't and I don't know why you would need this, seems like might be future maintenance. Again I only have experience with ours. I don't know what the cost savings over time is. I know in my own house I have a timer set on my regular water heater to save money and I can tell you I have had 3 time clocks fail almost one after another, in 10 years I think I am on my 4th or 5th humm how much money did I save there? Plus there have been plenty of times I have had to wait around waiting for the water to get hot and plenty of times we ran the tank down and finished up cooler then desired. I wish I had pushed for my house to get a panel when my parents were getting theirs replaced. I am kicking myself hard for that one. Anyway... In short it's a win win.

    Bookmark   September 10, 2010 at 1:36PM
Thank you for reporting this comment. Undo

We've been in the house for 5 months now and I'm absolutely thrilled with the decision to get the solar heater. It's 80 gallons and works perfectly.

The water gets very hot but there's a regulator on the tank to adjust the temp. The first time my son used the Jacuzzi, he ran the 80 gallon tank out of water! It hasn't happened since though.

The tank cost $8400 upfront which was kind of hard to swallow but with credits and refunds from the state and Fed, it cost us about $2600.

I'm sure we've saved at least $50 a month in electricity by not having to heat and continually heat water in a standard tank.

    Bookmark   September 11, 2010 at 9:14AM
Thank you for reporting this comment. Undo

Did you go with any type of backup?? Also, what company did you use? I am considering a similar situation on my Louisiana home.

    Bookmark   April 7, 2014 at 4:12PM
Thank you for reporting this comment. Undo

I personally suggest that you have to visit both type of systems first if available nearby, this will give you the most accurate information about pros and cons of each

    Bookmark   April 21, 2014 at 12:36AM
Sign Up to comment
More Discussions
Geothermal issue
I don't know whether to post this under renewable energy,...
if you must use solar, consider this option
first of all, for renewable energy i much prefer the...
Radon system
Can somebody tell me why there's condensation outside...
Ideas on how to capture gray water runoff from A/C?
The pipe that comes out of our crawl space which empties...
Energy usage has increased since net metering installed
My electricity energy usage had never exceeded 700kw...
Sponsored Products
Eurofase White Domed Shower Trim
Euro Style Lighting
Italian Courtyard Slate Indoor-Outdoor Fountain
Lamps Plus
Urchin Mini Pendant
Safavieh Indoor/Outdoor Black/Natural Polypropylene Rug (4' x 5'7")
Armstrong One-Light Black Outdoor Wall Light
$160.00 | Bellacor
Designers Choice Collection Ceiling Fans Fern Leaf 52 in. Oil Rubbed Bronze
Home Depot
People viewed this after searching for:
© 2015 Houzz Inc. Houzz® The new way to design your home™