Pure Waste Challenge, Part II: Take Action, Go Tankless
by Collin Dunn, Corvallis, OR, USA on 10.25.07
In part two (here's part one) of our spotlight on the Pure Waste Challenge, we'll help bust a few myths about tankless water heaters and hopefully inspired you dear readers to take action against global warming. It's easy; here's how it works:
1. Read the primers.
2. Ponder the possibility of making some easy, meaningful changes in your life.
3. Send a quick email (details below the fold) to confirm that you've done both of those.
Once you click "send," the Hinkle Charitable Foundation (HCF) will donate $100 to the Solar Electric Light Fund (SELF), a very worthy non-profit working hard to simultaneously combat global poverty and climate change. It's that easy. Think about how many emails you'll send today, and consider adding one more. Hit the jump to learn more about SELF and play some fact vs. fiction with tankless water heaters.
SELF’s primary mission is to bring solar power and modern communications to rural villages in the developing world. In many instances, SELF’s installations are directed to education, health and irrigation facilities and can include joint ventures, where local participants invest in a portion of the project. Providing solar electric power to remote, off-grid people frees them from the unpalatable alternatives of either using kerosene-generated power (which is both bodily and environmentally dangerous) or living with no electricity, no lights, no irrigation possibilities, and no connection to the outside world.
The second primer is all about reducing the energy you use heating hot water by using a tankless water heater (see more coverage of them on TreeHugger here and here). Hot water usage in American households consumes between 15% and 30% of a home’s energy demand, according to the US Department of Energy. Surprisingly, the technology used to heat water in the US is antiquated and highly inefficient when compared to the tankless or on-demand technologies now used regularly in Europe and Asia. This primer attempts to explain the new technology and benefits behind whole-house natural gas-fueled tankless water heaters (TWH).
Myth 1: Only a tank can provide a large amount of hot water.
Heating a tank of hot water is neither an effective nor efficient way to supply hot water. As hot water drains from the tank, in-flowing cold water lowers the overall temperature of the water in the tank. Traditional tankbased water heaters are not designed to heat the inflowing cold water rapidly enough to keep the outflowing water at a constant temperature. In contrast, properly sized TWH systems are designed to keep outflowing water at a constant temperature.
Myth 2: A tankless hot water system can’t provide enough continuous hot water for an entire home.
The reality is that the heat-exchanger technology used in TWHs is specifically designed to provide a full and inexhaustible flow of appropriately heated water to an entire household.
Myth 3: Tankless water heaters must heat the water so hot that it is dangerous to use them.
Actually this fear is more relevant to traditional tankbased water heaters than to TWH systems. Tankless systems are safer to operate since they heat the water to only slightly above the level of intended use. Traditional tank-based water heaters have to overheat the stored water so that it will remain hot enough as the in-flowing cold water mixes with it.
Myth 4: Tankless water heating systems cost more to operate.
Like any profitable investment there is an immediate outlay of cash, but when you factor in the lower operating cost and longer (20-year) service life, TWHs save their owners a substantial amount of money. In fact, as illustrated below, it is difficult to construct a scenario where owners of a new natural gas TWH system will earn a return on investment of less than 45%.
Sounds pretty good, right? If something like this sounds worthwhile (along with the other primers that are part of the challenge, available here), we encourage you to fire off an email to purewaste(at)thehcf(dot)org with your name and e-mail address where you'd like the acknowledgment sent, and the Hinkle Charitable Foundation will make a grant to SELF. Stay tuned for the final primer, but you certainly don't have to wait for us to take action and write that email.
::Hinkle Charitable Foundation and ::SELF present the ::Pure Waste Challenge
Natural gas is great, I guess, but I can't get it from the sun or wind. I'm not a fan of microwaves, as I prefer low-tech goodies. Are there electric instant hot water heaters or is electricity too slow to heat water on the fly? Can a solar hot water system pre-heat the water to make the instant-on systems more efficient?
There are most definitely electric tankless water heaters. I should know; I have two of them in my house! I am not sure why the author of this explicitly mentions natural gas, when electricity can be derived from the wind and the sun to operate the water heater. The reason I have electric tankless heaters is because I do have solar photovoltaics on my roof.
You can use solar pre heat with a tankless hot water heater, but you either need a tempering valve or a model that will adjust to set temperature point.
I just got a Rinnai tankless water heater installed. V2532. Works very well. Especially good for showers. Another advantage not mentioned is that you can locate it much closer to your points of use. Also tanks (unless kept extremely hot (140) contain bacteria. Tankless do not, and can be operated at a lower temperature.
The only draw back is that it does less well when the tap is turned on and off often as when you are hand washing dishes. the water only gets lukewarm. Works best with a continuous flow.
"designed to provide a full and inexhaustible flow of appropriately heated water"
If you need that, you'll save a lot more energy by figuring out how to conserve hot water than by switching to a tankless heater.
Tankless has real benefits by it's overhyped. Drainwater heat recovery, solar water heating, and basic stuff like insulating hot water pipes and using well insulated tanks should be the emphasis here.
I also installed a Rinnai in the three unit apartment building where I live (three bathroooms, with 5 people total.) The tankless replaced a single 50 gallon gas tank water heater.
Because it was one water system for the entire building the heater is far from most points of use - and ideally you'd install it as close as possible to where it's used.
And i agree for times where you are doing a lot of on/off cycling such as handwashing dishes - it's not ideal.
But for situations like several people, in three households, taking showers in a short period of time (i.e. every weekday morning) it works quite well. I expected complaints from my tenants, and there have been none.
Simply it doesn't run out of hot water in the morning. Also, it can't rust out and dump 50 gallons in my basement, and it takes up much less space (since it's on the wall.)
Hard to say exactly, but looking at the summer months that we have had it vs. the year before when we did not - it looks like we use about 10 less therms of gas per month. Not huge numbers, $$ wise ... but when / if gas prices rise - it's nice to know we've taken a step towards being more efficient.
"SELF’s primary mission is to bring solar power..."
"The second primer is all about reducing the energy you use heating hot water..."
The only way you will help anything is by combining these two ideas and go with solar hot water. Its the only way to be self-sustaining and carbon-neutral. Even going with an electric tankless unit powered with solar PV isn't a great solution (or even a good solution), since PV is so inefficient compared to solar thermal. Make heat from heat, directly! Certainly going with a gas-powered tankless unit is the second-to-last option you should consider when replacing a water heater today (the worst being a gas-powered tank unit). We are almost at "peak NG", just like we are already at "peak oil". Relying on NG for part of your home's energy source will only become more expensive in the future, and is non-sustainable or carbon-neutral.
My long-term goal will be to install a solar thermal system that provides domestic hot water plus radiative floor space heating. Supplemented with a ground-sourced heat pump system for the days when the temps drop below 20F. I'll still have my trusty wood stove as a final backup, but as much as I love its heat I hope I won't have to use it ever again. Yes, solar PV will be installed, too.
just for reference,these are "cold water heaters" not hot water heaters as you and everyone keep calling them...
We live in a downtown condo, and currently have a no-kidding-80 gallon water tank. This is great for filling two jacuzzi's back to back( which never happens!) but just generally means we have too much hot water stored for two people on most days. We also worry about the tank letting loose on our neighbor downstairs( which has happened in everyhouse I have owned, eventually). So we inquired with our plumber about a tankless system, and he came up with a million reasons why we can't... something about the size of the vent that carries emission from the furnace( gas fired hot air) and the current water heater.
Does this sound right??
We live in a downtown condo, and currently have a no-kidding-80 gallon water tank. This is great for filling two jacuzzi's back to back( which never happens!) but just generally means we have too much hot water stored for two people on most days. We also worry about the tank letting loose on our neighbor downstairs( which has happened in everyhouse I have owned, eventually). So we inquired with our plumber about a tankless system, and he came up with a million reasons why we can't... something about the size of the vent that carries emission from the furnace( gas fired hot air) and the current water heater.
Does this sound right??
A lot of plumbers are not that familiar with tankless water heaters and are prone to be negative about them. They tend to subscribe to the old myths and have little experience to counter those myths.
In the case of the plumber saying you can't replace your old gas water heater with a tankless model because of venting issues, he may be right. But that isn't the end of it.
A tankless model burns more gas per second than a tank model. Therefore there are more combustion gases that need to be vented, per second. Your old unit probably has a 3 or 4" vent and with a gas tankless unit, you will ikely need a 5" or 6" vent.
So, you could repalce the vent at the same time you replace the water heater. You could relocate the water heater to a new location more easily vented. You could choose an electric heater that doesn't have any combustion gases.
I installed a tankless unit and we had to upgrade the venting. Instead we moved the entire unit to outside of our home and did a little replumbing for the water lines. We could of upgraded the venting, but we wanted the interior space to build a linen closet.
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