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by Gordon Gray, 02/13/07Gordon Gray has rebuilt his own home and remodeled two-unit and four-unit buildings. He is now remodeling his second home.
1. Determine your hot water needs.
In general, the hot water flow rate of a small tankless water heater can support a bathroom and a kitchen with a dishwasher. The key to selecting the proper model is knowing the flow rates of your fixtures, the coldest temperature of incoming water, and your usage patterns (how many faucets do you expect to be able to use at the same time?). Work with your plumber to choose a size that fits your needs.
You can also install more than one heater to heat water by zone. For example, at my current remodel I’ve installed two tankless water heaters—one supports a kitchen, bathroom and half bath; the second supports two additional bathrooms.
2. Understand your dishwasher and clothes washer.
Your appliances may need hot water from your tankless heater or they may heat water internally. I bought a super-efficient Asko clothes washer/dryer that heats the water itself and requires only a cold water connection. I didn’t realize this until we installed the appliance!
3. Be prepared for resistance from your contractor.
Because of concerns about time and liability, most contractors don’t want to try something new. If you are convinced that a tankless water heater is for you, insist on it and find a contractor who will work with you (preferably one who has experience installing tankless units). Provide the contractor with the manufacturer’s installation instructions (often available online). You may also want to contact the manufacturer’s technical support department for advice on size and other considerations.
4. Carefully plan the location of your water heater.
Tankless water heaters use an intense flame to heat water on demand. They require more air for combustion and vent more exhaust than conventional water heaters. This affects how and where you install them in two ways:
Venting: For direct venting (through the wall), the vent termination must be at least three feet from any operable window. If you are venting through the roof, the length of the vent is determined by the size of the heater (the BTU output) and the number of elbows, or turns, in the vent. You may not be able to vent the heater through the roof if the vent run is long—for example, if the heater is in the basement of a three-story building.
Combustion air: A gas-fired water heater (tankless or not) requires a source of oxygen for combustion. To avoid back-drafting that combustion air through another appliance's exhaust pipe, your water heater should be sealed-combustion direct-vent.
5. Check your gas and water supplies.
Tankless water heaters can produce three to four times the BTUs a conventional heater produces. Your plumber must verify that your current gas line size, length and even gas meter can provide sufficient gas flow to the unit. Tankless heaters also require minimum water flows for activation; again, your plumber should verify that your supply meets the specifications.
6. Avoid long runs between the heater and the faucet.
Because tankless heaters generate hot water only when you turn on the hot water tap, it takes some time (a small delay) to heat cold water to the optimal temperature. Locating the heater far from the tap can result in a more noticeable "sandwich effect" when hot water is used intermittently. One way to overcome this problem is to use a recirculation pump that brings water from the farthest fixture in the plumbing run back to the tankless heater, but because these pumps use a lot of energy keeping water in the loop hot, it's better to preheat or buffer hot water.
For details on preheating, read GreenHomeGuide's Get Optimal Performance from a Tankless Water Heater.
7. Make sure you meet the building code.
If anyone—you, your plumber or the building inspector—misses a detail during preliminary reviews, you’ll have a messy and costly fix to sort out later.
8. Make sure the venting material complies with the manufacturer’s specifications and local building codes.
I’ve found that the venting material for tankless water heaters is specific: it is made of stainless steel and has seals built into it to prevent carbon monoxide from leaking into the home. Double-walled material may be required, depending on your design (be prepared: it is expensive). Your plumber or HVAC contractor may miss this specification.
9. Be patient and prepare for building department reviews.
In my experience, some building department staff members are up to speed on tankless heaters and some are not. There can be a disconnect between the plan review personnel at the building department and the on-site inspector for your project. Be prepared for hesitation and confusion on either end of the permit review and inspection process. Keep the installation specifications and the manufacturer’s tech support number on hand—they can make life easier for all involved in the project.
For more information:
We found generally good reviews for the natural gas powered Takagi T-K2 and the Bosch AquaStar 2400E. These are large "whole house" water heaters.
For a smaller application (i.e., one bathroom) consider the Bosch AquaStar 125B or the electric Bosch PowerStar AE125.
On February 19, 2007, Jim wrote:
Tankless heaters save space. They can be installed outside, great for additions. These heaters have an endless supply of hotwater. There is a $300 federal tax credit for heaters below 200,000 btu’s for 2006 and 2007. Save energy! They do need access to a larger gas supply.
On February 22, 2007, Tom wrote:
I am told the temps vary from tankless heaters as one is taking a shower of doing the dishes. Is there a heater that keeps this from being a real problem?
On March 3, 2007, David wrote:
Temps will not vary with a properly sized tankless heater. Check out Takagi tankless heaters for instance. Can easily support taking a shower and doing the dishes.
On April 3, 2007, Caprice wrote:
We had tankless hot water heaters in Portugal when we lived there from 1995. It made the US standard seem sooooo wasteful. They were always efficient and inexpensive. We are building a new home in N. Calif and want to have 2 of them in our home. I’m doing research on how to actually install them. I’d like to have them in the attic area and out of sight. Would this be a problem? In Portugal is was common to have them install inside an upper cabinet for easy access.
On June 22, 2007, Tim wrote:
In researching the possibilities-- I have discovered that not only is there a federal tax credit of 300 bucks. If you live in Oregon-- they’ll kick in another 400 dollars towards the installation.
On June 28, 2007, Frank Lee wrote:
What about electric tankless. Ther is no venting. the circuit connections a very large. Are electric tankless as advisable as gas.
Also is there such a thing as an oil firred tankless?
On June 30, 2007, Caprice wrote:
Actually, we are into propane as we don’t want to depend on electricity to have hot water. Yep, we are very rural.
We did decide to install them kinda high, but not in the attic space. The bottom of the unit will be about 5+ feet off the bottom of the floor.
Thanks for the mention of electric tankless. I had no idea they existed. I would still encourage anyone to get away from keeping 30 to 50 gals of water hot just to have it ready- Seems like a horrible waste.
On August 19, 2007, Hola wrote:
In the marine industry, this is used often. They have a diesel fired “furnace” to heat the boat, and this also provides a virtually endless supply of hot water.
On August 19, 2007, Caprice wrote:
Actually that system in the house makes the best sense for hot water baseboard heat. Not sure if it is used, but passive hot water heat sounds good. We are still working away on our home. If anyone wants to see the progress.... http://www.whymzy.com (go to the link mentioned in the welcome area on the front page.) We mounted our first on demand heater near the ceiling, but still can reach the controls. We plan to mount the second one the same way.
On September 27, 2007, Danielle wrote:
Rinnai makes fantastic tankless water heaters. They are becoming much more popular, and are far less wasteful. Their website is foreverhotwater.com, and it’s very informative. There are more and more installers becoming familiar and certified in the installation of the product.
On September 28, 2007, Frank Lee wrote:
Electric Tankless for whole house ----> is a different animal than gas fired tankless. I would really like to get feedback from anyone with personal expertise or at least experience selecting and using whole house electric tankless. Issues of concern:
- circuits would become the biggest in the panel like 3x 40amp or 2 x 60 amp. Are there voltages drops “brown outs” in the house when DHW kicks in?
- brand and model comparisons, are some energy smarter or more durable than others?
- user experiences
- How about a smaller amp electric tankless as an after booster above the conventional electric tank set which is set at 85 or 90 degs. Now the tank becomes a powered tempering tank with lower heat loses; booster is now a reasonable amp draw - seems like a viable approach. Any thoughts on this?
On October 6, 2007, c.alex wrote:
I have installed several heaters made by Noritz. They are simple to install, have plenty of options, and the manufacturer is very helpful if the need arises. As a company, their impact on the environment and natural resources is quite favorable. Check them out http://www.noritzusa.com
On December 6, 2007, Pierre David wrote:
I am seriously considering going with a tankless, but have consulted a few local tradesmen and they offered some negative feedback, though I suspect because they are biased. I live in a rural setting, and am on a drilled well. They advise that tankless systems arent very effective on non municipal water systems because of the much lower water pressure, that the flow at the tap gets significantly reduced. Is this a fact?
On December 14, 2007, Kevin Casper wrote:
Water pressure on a drilled well depends on the setup. I used to live on a farm with a drilled well and we had greater water pressure than the local town did at the time due to a good water pressure tank setup that supplied the entire farm’s water pressure. It isn’t the fact that you have a drilled setup that is a concern. You should have the water flow tested under load to see if it meets requirements. If it doesn’t, there are many ways to increase the flow if you can afford to do so.
On January 4, 2008, Ralph wrote:
We recently drilled a well at the cottage. If you install a constant pressure pump you’ll have the same water pressure from the moment you turn the tap on until you shut it off, a huge difference from the standard type water tank.
Want to share your experience? Post a comment here.
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