Tankless or tank water heater question

chaocaiNovember 3, 2011

First sorry for re-posting but I was advised to post here from instead of HVC forum as it seems that I picked the wrong forum initially.

We currently have 2 tandem water heaters, one being gas one being electrical. one is 80 gal and another 95 gal. They are tandem connected e.g. One dumps to another. I don't understand why they are set up this way btw. so the water distribution is not zoned. They both are over 15 years old. In my area, the utility company offer an energy saving program to convert from elec to gas. By doing that, we get reimbursement for replacing elec. water heater with gas. We are thinking to replace both old ones with either traditional higher efficiency gas heater or tankless gas heater. the furnace/water heater currently sit in the middle of the house in the basement closet. Bath and kitchen lay on each end of the house. So in order for the water to go to bath or kitchen, it has to travel half of the house distance either way. We have a relatively big house > 3000 sqft. We have two concerns with tankless option:

1. How would it work with bath/kitchen layout above? Would we have problem igniting the tankless since the hot water faucet is on two ends of the house while the heater is in the center?

2. would tankless wh supply enough water for a 4-5 people staying during holidays? The worst case is more than 1 people taking shower at the same time using two/three bathrooms.

Thanks for your input. Your opinion is very appreciated.

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live_wire_oak

There are 143 results from "tankless" on just the Plumbing Forum. Reading those past threads should educate you enough to make your decision.

The summary would be that it is an expensive choice for retrofitting compared to just replacing a conventional water heater. You have to be willing to live in the home 30+ years to see any payback. It's a great choice for a new build, where you can build in the different infrastructure that tankless needs in order to be successful in your climate.

Here is a link that might be useful: ''Tankless'' search results

    Bookmark   November 4, 2011 at 1:48PM
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jakethewonderdog

First, I'm going to assume that we are talking about domestic hot water and not used for heat.

It could make sense to use two tankless units - one on each end of the house.

Ignore any claims of "high efficiency" when comparing gas water heaters; Use actual numbers. A "high efficiency" standard gas water heater is about 67% - a non condensing tankless is 85-87% and a condensing tankless is 90-95%.

Tankless water heaters are more expensive than tank heaters, but you really need to know the details: If you have to install new gas lines, forget it. If not, it can be reasonable as long as your installer doesn't inflate the cost.

Self installed, mine was about $1,100 with the vent kit and valves. Payback was 6 years (over standard tank)and I have continuous hot water. Your mileage may vary.

Regarding the sizing: That needs to be determined with actual numbers.

    Bookmark   November 4, 2011 at 4:06PM
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weedmeister

And don't assume that since you have an existing gas furnace that you have enough excess capacity from the meter to fire up a gas tankless heater. This has to be checked and confirmed. Running a new line and installing a meter with greater capacity would be costly, especially after the fact.

    Bookmark   November 4, 2011 at 5:24PM
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aidan_m

My choice setup is the whole-house tankless heater installed as close as possible to the bathrooms, and a small point of use heater under the kitchen sink. Tankless heaters can have low-flow issues with the dishwasher, or kitchen sink use. This is easily corrected by putting a 2 gallon electric heater under the kitchen sink, and feeding it from the tankless unit. It doesn't have to do much heating. It just mostly stores hot water and keeps it hot, ready for washing dishes and hands.

    Bookmark   November 4, 2011 at 5:32PM
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chaocai

Thanks for the advice everyone. The contractors said my house set up doesn't allow tankless. Plus your precious input, I guess I stay with tank gas now. But here is another problem. Going with 50 gal .62 pilot fire model, we would survive power outage with hot water supply. But it's not Energy Star qualified. Hence no rebate. If we go with .67, not only the installation cost goes up as much as $900, but also we would end up with no hw during power outage. How different is .62 vs. .67?
We have two quotes in now, each ask for > $2000 cost for .67 tank gas wh. With .62, it's about $1200.

    Bookmark   November 7, 2011 at 5:45PM
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jakethewonderdog

I'm a big advocate for energy conservation, but this is a difference that doesn't matter.

Go with the .62 unless the rebate covers the difference.

Add pipe insulation if you want to reduce heat loss.

    Bookmark   November 8, 2011 at 9:16AM
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chaocai

Thanks! good advice appreciate it. So for tank wh, does anyone know how Rheem compares with Bradford White? It seems different company sell different products. Is there any specific features/spec's I should pay attention to?

    Bookmark   November 9, 2011 at 1:19PM
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jakethewonderdog

Bradford White limits their product to plumbers, and some people swear by them. They are typically more expensive. It could just be that because of that limitation, they are more likely to be professionally installed.

Marathon uses fiberglass tanks.

Other than that, I'm not sure there are a lot of differences between brands.

My opinion is that you go with the moderate priced unit - and know that you are going to replace it in 10-15 years.
That estimated time line seems to hold true if it's an expensive tank or not.

    Bookmark   November 10, 2011 at 8:16AM
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