Tankless Water Heaters

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Permalink Reply by SustainGigs on December 30, 2007 at 9:01pm

Jordan,

Found some of this on a tankless water heater site:

Tankless water heaters only use energy when hot water is being used will likely save you more money over their expected life of 20 years than they will cost upfront. Besides energy efficiency, tankless water heaters are much smaller and easier to maintain.

The payback period for tankless water heaters is 3 to 7 years depending on how much hot water used in your home and your specific cost of energy. The smaller the amount of hot water that you use, the faster the payoff. If you are single and are seldom at home using hot water, your energy bill reflects the low consumption because tankless water heaters do not experience standby heat loss.

If you have a tank, then you are limited to 40 gallons of hot water per hour (That is barely enough for a 20 minute shower in one hour time period!) and you still have to pay for standby loss, which is about 15-20% of the energy bill.

When the water heater is actually used to heat the water, the tank type water heaters are 40% to 60% energy efficient (the rest of the energy is spent to heat the exhaust and walls of the tank!), while tankless water heaters are 80% (gas) to 99% (electric) efficient. When you don't use hot water, you can save up to 15%-20% of your energy bill with the tankless water heaters, because tank type water heaters are subject to standby heat loss.

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Permalink Reply by Jenny on January 20, 2008 at 6:16am

I have a tankless water heater. I love how it leans against the wall in its box. When/if/ever it is installed, I will tell you all about it... a couple of things I ran across while researching before purchasing: 1) tankless water heaters turn hippies into hippocrites as they inevitably take longer showers & 2) if you're really, truly reducing your hot water use, the more efficient purchase may be an electric model as opposed to propane, and of course then you could one day connect it to your solar panel. My model is a Rinnai, but a local company here in Vermont that has made them for decades recently sold to
Bosch. Also worth mentioning, the insulated vessel of the tank heater that you have now is actually somewhat valuable - don't just throw it away! The most in demand use for those is as a hot rainwater collection system ( I think.)

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Permalink Reply by James Baker on February 6, 2008 at 10:52am

Hi Jordan,
Takagi, Rheem, Bosch, Rinnai and Noritz are some of the bigger manufacturers. I've had a tankless heater (a Takagi TK1-S) since we remodeled 2 years ago and I'm a big fan. It has been able to keep up with showers, dish washing, and laundry for our family just fine. In addition to the advantages already mentioned there's a few issues you should be aware of.

-Electric models in general do not have the heating capacity that gas models do, so make sure you pick one that can keep up with your water needs.
-If you get a pilotless gas model (you should) it will probably need electricity run to it. Larger gas units also need electricity for the vent fan.
-If you want to put it outdoors, make sure you pick a model that's rated for outdoors.
-Gas models use a higher flow of natural gas when on than tank models, the gas pipes need to be large enough to supply the flow without too much pressure drop. There should be a table in the installation manual.
- Larger gas models have special venting requirements because the combustion air is fan driven. Category III stainless steel vent pipe. If it's outdoors and more than 4' from a window you can sometimes avoid vent pipe.
-There is a minimum flow rate to turn on at all. For mine, it needs 0.75 gpm to turn on, and 0.5 gpm to stay on. This means that if you run hot water somewhere in your house at a lower flow, the heater won't turn on and cold water will run through the hot water pipe.
-It's not clear to me whether a tankless heater, at least a gas model, will work with solar hot water. If anyone wants to talk about this subject let me know.

Take a look at the installation manual for the one you like to see whats involved. Hope this helps.

-James

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Permalink Reply by Forbes Bagatelle-Black on February 13, 2008 at 4:49pm

What?! The Bakers have RUNNING WATER in their house now?! Living the life of ease and luxury, I see. Next thing we hear, you'll have heat... - FBB

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Permalink Reply by rripken on May 12, 2009 at 10:40am

I don't have either but I don't see why a tankless water heater wouldn't work with solar hot water system. The solar could pre-heat the incoming water. What doesn't make sense together is a tankless heater with a hot water recirculating pump.
My brother in-law replaced his water heater in the basement with a tankless one. He ended getting an outdoor unit and mounting it on the side of the house b/c it was too expensive to put all the vent pipe and safety equipment in the basement. I think he really likes it except he has one bathroom sink that doesn't use enough water to trigger the heater.

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