Opinions on tankless water heaters

[Mr.X]

I am replacing a 70 gallon gas fired regular water heater. I am considering the option of using a tankless water heater so as to be greener. The home is located in the Northeast United States. I imagine the water coming in during the winter will be in the 40F or lower?

I have been looking at units from Rheem, Bosch, Rinnai etc. and was just wondering what experience folks have had with their tankless units. From my internet perusing it seems opinion goes both ways.

Thanks. Mr. X - Trying to go green

 

[jmorriss]

Just b/c something is "Green" doesn't always mean it will be cost effective. You need to know how long it will take to see a return on your investment-for stuff used in homes, people on average move every ~5 years in the US so keep that in mind.

In this case what I have read/seen you need a beefy gas line (1/2" won't do, you need something in the 1" range) to supply sufficient gas to the heater to reduce lag. You also really need the plumbing set up in such a way that it recirculates when not in use, thus less waste when waiting for the hot water to come out of the tap. This is also crucial as I seem to recall that it takes a pretty decent draw to kick the heater over and start the cycle. Just somethings to consider. Based on the info I have seen and talking to builders I wouldn't bother with it unless I was doing a new house or a to the studs renovation.

 

[mike_s]

Mr X, send DiverAL a PM. he put one in his house a couple years ago.

You also really need the plumbing set up in such a way that it recirculates when not in use, thus less waste when waiting for the hot water to come out of the tap.

huh? w.t.f. ?

where the heck did you come up with that idea?


that defeats the purpose of having an "on demand" water heater.

the purpose of the "on demand" water heater is to ONLY heat water when you need it. not to heat it all the time.

If you set up a pump to circulate water through all the lines in the house so that the water coming out of the tap is "hot" all the time, it uses more energy in pump and in water heating, even when using a conventional tanked water heater.

If you try to do the same thing with an "on demand" (tankless) water heater...... then it defeats the purpose of it being "on demand" because the thing would have to run most of the time to re-heat the water being circulated.

 

[Scott]

Rinnai heaters are nice but you'll pay a bit more for them than say a Rheem. Rheems are less for a reason.

In this case what I have read/seen you need a beefy gas line (1/2" won't do, you need something in the 1" range) to supply sufficient gas to the heater to reduce lag.

Gas line size is based on distance and combined BTU's of all appliances. If you're replacing a 70,000 BTU (70 gal) tank water heater with a 70,000 BTU tankless it's still 70,000 BTU. The problems arise when you take a 40 and replace it with a 70.

ROI will vary. I suggest before making the plunge do some serious number crunching. Check with local gas utilities to see if they offer any incentives. In my real job we look at these when we building small buildings or when we need to replace a water heater in an exisiting location. Sometimes it's cost effective others times it's not.

Some good info: Gas Tankless Water Heaters : ENERGY STAR

Savings calculator: FEMP Energy-Efficient Products: Energy Cost Calculator for Electric and Gas Water Heaters

 

[Mr.X]

Thanks guys. I appreciate all and any feedback. The Rinnai comes with a nice tax break. Up to 1500.00 I'm sure others do too? Rinnai's are pricier, but seem a better unit all over. R0gue & Mike - I appreciate the links and referrals to others on SB!

Also, in the near future I am considering adding solar panels to the roof to augment the new water heating system. The tankless heater seems like an easier unit to fit with such a system. However, I don't think I'll be doing this in the next 3-5 years.

As per return of investment - Yes. I don't think I will see it for a while, but the existing tank in this new "Scuba Shack" is waaaay past warranty and probably on its way to failure in the not to distant future. It's something like 7 years past warranty. So I figure I'd rather spend the anticipated labor costs in getting something that won't need replacing, or dumping for a while. I just feel guilty about using and dumping stuff out these days.

Thanks again.

X

 

[Peter_C]

Also, in the near future I am considering adding solar panels to the roof to augment the new water heating system. The tankless heater seems like an easier unit to fit with such a system. However, I don't think I'll be doing this in the next 3-5 years.

X

That is the exact reason we went with a tanked water heater. Our decision was based on a visit to our local solar institute, where we learned a solar water heater was the BEST return on investment for cost applied.

Either way, insulating the pipes makes a big difference.

Back East a heat pump would probably be an expensive, yet worth while investment.

 

[drbill]

Mr.X. you might be interested to hear that the City of Avalon is considering a program to allow residents to pay $100 per month over 20 years to have solar panels installed on our homes. These are for electricity rather than hot water (but my water heater is electric). If your electric bill is over $100/month currently, this should bring significantly savings as the utilities raise rates over the next 20 years.

 

[mike_s]

Mr.X. you might be interested to hear that the City of Avalon is considering a program to allow residents to pay $100 per month over 20 years to have solar panels installed on our homes. These are for electricity rather than hot water (but my water heater is electric). If your electric bill is over $100/month currently, this should bring significantly savings as the utilities raise rates over the next 20 years.

does Avalon get it's power over a "big undersea cable" to the mainland or via generators on the island?

how much is electricity per kWh there? (kilo-watt-hour)

 

[Peter_C]

Mr.X. you might be interested to hear that the City of Avalon is considering a program to allow residents to pay $100 per month over 20 years to have solar panels installed on our homes. These are for electricity rather than hot water (but my water heater is electric). If your electric bill is over $100/month currently, this should bring significantly savings as the utilities raise rates over the next 20 years.

I would jump on that immediately if they offered it in our area. The ROI here is around 5 years currently which is not bad. With solar you want an electric hot water heater. Most people I know around here with solar have less than a $15 monthly power bill, compared to my $100+ a month bill.

 

[cmburch]

I have a Bosch and my sister has a Takagi.

A normal tank water heater. The water is hot in the tank. You turn on the hot water and the time it takes to get to the faucet is related to the distance of the hot water pipe.

A tankless water water heater needs to heat up the water. So while the heater is going you are wasting water. Cheaper on gas, but waste some extra water.

Possible solution hot water pump at furthest bath. Turn on in morning or when needed. It pumps the hot water back into the cold water and has a thermostat to stop pumping. These are normally designed for tank water heaters with a special insulated hotwater line to the furthest bath.

There are many different configurations of tankless. Pilot light, electronic and hydrogenerated ignition. All are pretty similar in that in order to increase or maintain the temperature the flow is reduced. Most companies make different models to handle 1 or 2 baths going at the same time.

My Bosch (Home Depot) sucks. It has a flow knob to adjust the temperature (less flow for hotter water) and hydrogenerated ignition. The safety feature on it shuts down the flame if it detects an increase in inlet water temperature or outlet water backpressure. This means you are taking a shower and the flame turns off whenever for instance you turn on more cold water too quickly or during the winter when there is a difference between the colder water above ground and warmer water underground. Then I have to shutoff the hot water and turn it on again and wait for hot water to get to the shower.

It is great for kid's baths since you never run out of hot water and for nice hot water for washing dishes.

I will use the Bosch for the laundry room on some rentals.

The next unit I will buy one that:
1. Install outside.
2. Electronic Ignition.
3. Large flow capacity = larger heat exchanger.
4. Flow valve and heating is temperature controlled so less adjustments.