Building new house with Tankless and re-circulating pump

monsoon99September 22, 2008

We are building a new house in s.california- has 2 bathrooms. 2 adults and one child. We are installing solar electric. We are going with the tankless water heater and since kitchen and one of the bathrooms is far from the TWH, we want to install the re-ciruclating pump. I would like to know WHICH BRAND gas TWH is best and which top brand pump would go with it. My plumber is telling me that putting a recirculating pump on most TWH voids their warranty and that I need a 5 gallon electric water heater to do the job. If true, is there TWH brand out there which works with pump without voiding warranty. What type of electric water heater is better quality? What else I should ask plumbers to do to make this system work well? Thanks for your help.

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Take a look at the Takagi TK3, it has power taps and circuitry built in to power and operate a recirc pump.
These are available in indoor, outdoor and indoor recessed models.

Guess that shoots holes in the plumbers statement since they make it easy for you.

The circ pump must be bronze or stainless steel and are available in many pipe sizes and capacities depending on pipe lengths and fittings. I prefer the Grundfos line for circs.

Here is a link that might be useful: Takagi TK3

    Bookmark   September 22, 2008 at 9:02PM
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For a gas heater, this is my recommendation also. You need to stay below the ratings given by the heater manufacturer to avoid damage to the heater over the long term.

But the poster said that they would be installing "Solar Electric" and is looking for an electric tankless. Help us out, what is "Solar Electric"? Is this solar heated water with electric backup or photovoltaic cells to power an electric water heater?

Using photovoltaic cells to power a tankless water heater really isn't feasible. Using Electric Tankless for whole house water heating rarely makes sense and makes less so as backup to a solar installation.

For electric backup to a solar domestic hot water installation use the storage tanks designed for that purpose. They store the solar heated water and have an electric element for backup.

    Bookmark   September 23, 2008 at 2:30PM
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He mentioned he would have solar electric and never said anything about an electric tankless.
I believe the comment about solar electric was to give us an idea about his intention to save energy.
As a PV panel can produce 175 watts at best, Not much there to support a heater with even alot of panels but will do well to power the on-demand, the circ and other items in his house.
The reference to the electric tank was by advice from his plumber to put at the far reach of the hot water piping to eliminate a long wait (commonly done before proper recirc could be added to on-demands).

While this is a good option for a remote kitchen sink, it's not advised for bathing as temp fluctuations will still occur from the small tank as cold enters before the hot gets there.

    Bookmark   September 23, 2008 at 4:00PM
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You are right about the tankless... the OP asked about a gas tankless and an electric water heater... Probably meaning tank.

That said, I agree with the Takagi recommendation, but I would still question the idea of a whole house tankless as a solar backup. Based on energy factor information, they save about 35-37% over a standard gas tank water heater but the payback is just marginal in the best of situations (low install costs, high energy costs) In a situation where it was only providing backup heat, it would never pay back.

If the overall goal is to save energy rather than make economic sense, use the $2000 to put insulation in the attic of a low-income household (2k would do several houses with volunteer labor) or pay for that same household to get a new 90%+ efficient furnace to replace their 70% efficient model that's being held together with a prayer. Two grand used that way would save a tremendous amount of energy.

    Bookmark   September 23, 2008 at 10:52PM
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Being that the OP is building a new house in S Cal., I doubt they are in a low-income bracket especially since they have already mentioned installing items in their home not typically within financial reach of poor people.

New home builds I doubt would have volunteers adding insulation to an attic that has yet to be built, to todays CA building standards.

    Bookmark   September 24, 2008 at 9:37AM
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I think this site had a technical problem and I could not find my post yesterday.

Anyway, Z1700 is right. We are installing solar electric panels for electricity usage. We are installing a gas tankless water heater. I have had to make some quick decisions and went with the Noritz outdoor water heater. I took Z1700's advise and went with the Grundfo recirculating pump. For someone else in a similar position, our plumber suggested I get one with a built in timer so that this pump will only come on in the morning and night when one is using the shower etc. The point I was making about the electric water heater was that if you attach the recirculating pump to the tankless directly, Noritz told me that would drop the warranty of the tankless to 3 years from 10. But if I installed a small electric water heater (I am using a 5 gallon one) and attached the recirc. pump to it then that would not diminish the warranty. This was plumber's idea. It will be months before we see how this system works out. From my limited understanding of the subject, the idea behind the pump is to make sure you have instant hot water at all points in the house saving water-waste from running water for 15 seconds to get to the hot water. The tankless is for unlimited hot water. Thanks for your inputs.

    Bookmark   September 24, 2008 at 7:26PM
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The whole idea of a tankless is so you only heat the water when you need it. A recirc on a tankless seems like a waste to me. Mount the tankless closer to the bathroom. That is the point of tankless heaters. You don't have a tank of hot water sitting there losing its heat into the house. Tankless heater don't have the insulation of the tank water heater.

    Bookmark   September 25, 2008 at 1:29PM
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I would have to say the biggest purpose of a tankless/on-demand is endless hot water at a desired temp.

An insulated recirc line works well as when the hot water returns to the heater it will only fire if it needs to raise the temp, and usually at the lowest firing rate due to minimal temp rise needed and flow rate provided.

True they don't have the insulation of a tank, but don't need it due to minimum water capacity and no, standby or flue loss like a tank.

Water heaters can't always be installed close to all fixtures, while I prefer to keep them close to laundry and kitchens, the master baths tend to be the distant runs. Many times two units are the best selection for many homes, in opposite areas.

    Bookmark   September 25, 2008 at 2:07PM
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My point about the insulation, etc in low-income households is that some people are more concerned about energy savings than making economic sense.(I'm not saying if that's good or bad) Sometimes they go too far into diminishing returns when, if they want to be green and save energy, they could do much more good by applying the capital someplace else -- possibly not even in their own home.

The OP cleared up what it was that they were trying to do and what the priorities were (continuous hot water). I'm not a big fan of long hot water runs and circulating pumps... but they can be smarter than wasting water.

For those who go this route, there are tankless units that are designed for use in radiant heat situations and have done the math on what amount of water flow through the unit is acceptable without causing excessive erosion. The Takagi TK3 is one of those.

    Bookmark   September 26, 2008 at 12:36PM
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