OT: Tankless Water Heaters

[joosttx]

Originally Posted by speedevil

The recirculating pump on the hot water supply is a great water-saver. Hot water in seconds, and for a very small electricity cost.

Ours uses a timer, so it runs in the morning, and then from before dinnertime until bedtime. It gave us a noticeable reduction in water consumption, and the convenience of hot water right away.

This is in a system with an 80 gallon conventional electric water heater. Tankless systems are not practical in our home.

this system has a recirculator built in. What is also cool is you can hook it up your wifi and set heating schedules and do all that smart appliances do.

[rwsaunders]

We installed a recirculating pump and a timer as a part of our hot water system when we built our home 20 years ago and the payback was quick with five people in the family. When our hot water heater eventually gives up the ghost, I’m going to explore installing a tankless unit.

[72gmc]

We just replaced a gas water heater that split at the base. Already had the recirc pump because the master bath with radiant floor heat is 2 floors up. The estimate we were given for tankless was more than 2x the tank replacement, and given our current bill I couldn't justify the cost unless we stay in this house much longer than we hope to.

[54ny77]

bingo.

it all depends on the length and the twists & turns of the run from the tank.

as well as supply pressure.

Originally Posted by Ken Robb

I don't understand why we would have to run water longer if it was heated by a tankless heater vs. a traditional heater.

A recirculating pump system would solve the wait problem for either heater, right?

[alancw3]

Originally Posted by NHAero

Electric is really only applicable at point of use for small flows, because the amperage gets so high quickly. To get a 65F temperature rise at 1.0 gallon per minute is 9.6kW, or 40A. Compare that to the smallest NPE Navien (the advanced model) at 150,000 BTU/hour, or 44 kW. That would be 183A at 240V.

on a recent episode of "this old house" they addressed the new generation of tankless electric whole house water heaters. from what i gathered the manufacturers have eliminated the problems of prior electric tankless heaters. you might want to do a search of "this old house" episodes.

[paredown]

We were early adopters, and installed a whole house large Bosch unit some years ago. I found out very soon that you should only use what the local plumber/supply house supports, because when I had troubles with it, I could not get anyone to do a service call for it.

If your guy is recommending Rinnai (which from prior reading has a decent rep), it is probably because it is stocked locally and he has had experience with getting it serviced.

When we talked about doing it here, our plumber recommended Takagi--again a decent brand--because of his prior experience with who stocked what and who was willing to stand behind it.

As far as usability, the only thing that took getting used to with the Bosch was that a trickle flow from a hot tap would not trigger it--you needed to really crack a tap for it to fire up. But it was rated at a 2+ device flow (not the little ones that HD used to sell), so you could shower with the dishwasher running without a problem.

[MrDangerPants]

Back in 1985, when my father was building our family home on Cape Cod, he installed a tankless water heating system. There were like 3 small units in the basement. I really think they're great especially considering we're not at the house year round. Back in 2012, right before my father died, he upgraded the system, probably for energy efficiency (he had solar panels installed around the same time). Don't recall the brand, though. Both systems have been trouble free.

[BikeNY]

Tankless water heaters are another one of those technologies(like ductless mini split AC/heatpump systems) that are use extensively elsewhere in the world, but are just recently finding traction in the US. I think it's mainly because our fuel/electricity costs are much lower than elsewhere, thus the added cost for efficiency doesn't get paid back very quickly.

Pick a reputable brand that your installer is familiar with and you should be good to go. Yes, there's more to go wrong, but they should be more reliable, and the warranties are usually pretty good.

Edit: No idea if these exist, but I remember years ago a company developing a tiny tankless heater that you could install at the point of use, like under your sink, for instant how water. You would install one in each bathroom(and kitchen) and nothing was needed in the boiler room. Or they could be added on to an existing system that had a long run to get hot water much faster. Not sure if they are still around though.

[Tandem Rider]

I have to agree with Pare, buy local, the local plumber knows where he can get in stock parts from, if it breaks, you don't want to wait 2 weeks for an igniter or a gas valve.

Second, a re-circulation pump will keep the instantaneous water heater firing whenever the pump runs (raising the gas bill), instantaneous heaters work on flow, but they work great on a tank type heater.

Third, the only way that a tankless is more efficient than a conventional is standby losses, if someone is home all day and uses hot water frequently, laundry etc, the storage tank type will have a lower operating cost. If the house sits for long periods, everyone is gone from 7 til 6 and then showers are one after another, then tankless saves energy.

[mnoble485]

About 6 years ago we decided to remove the water heater and go tankless. I called the gas company and the did the rest. Plumbing, gas line reroute etc. Added small amount to the bill each month until paid off. Rinnai, never looked back.

Mike

[glepore]

The maintenance issue mentioned is a cleaning of the heating coil, necessary in areas with hard water more frequently than areas without.

Navien has units with a secondary heater for radiant floor heat, although for a small area (Euro style concrete floor shower) I'm exceedingly happy with the a small electric unit available on Amazon for under $200.

[paredown]

Originally Posted by glepore

The maintenance issue mentioned is a cleaning of the heating coil, necessary in areas with hard water more frequently than areas without.

Navien has units with a secondary heater for radiant floor heat, although for a small area (Euro style concrete floor shower) I'm exceedingly happy with the a small electric unit available on Amazon for under $200.

Yes--single source/combi boiler for a small house is the perfect solution--but you can run it through baseboard as well as underfloor. This is our solution for the last Habitat house. Add a mini-split for A/C if needed and you have a pretty nice combination.

Our rental in Germany used a really nice Bodus single source boiler that did potable HW as well as in floor (Heizenboden) on the main floor, and radiators on the ground floor. One of the odd things that is happening is that the two categories are starting to blur--"boiler" and "hot water tank" can easily be the same device, and you can scale according to size.

The great thing about tankless (and part of what pushed me in that direction) is that if you are occupying the house only occasionally (like a vacation cottage, or as we were-commuting back and forth), you aren't wasting energy keeping a large tank of water hot when no one is using it...

[fixieporteur]

+1 for Rinnai. Had it for 7 years, and had it serviced once for $175 -- which it didn't really need.

[paredown]

Originally Posted by BikeNY

<snip>

Edit: No idea if these exist, but I remember years ago a company developing a tiny tankless heater that you could install at the point of use, like under your sink, for instant how water. You would install one in each bathroom(and kitchen) and nothing was needed in the boiler room. Or they could be added on to an existing system that had a long run to get hot water much faster. Not sure if they are still around though.

Yes those are still available, and they make a lot of sense if you have long runs from a conventional tank. They're pretty easy to install (the ones I have seen are electric), don't draw too much electricity and run only when the tap is cracked.

Absolutely great addition to a house in areas that have limited water--we waste a lot of water waiting for water to get hot at the tap--especially with bathroom faucets that by law mix cold in with the hot to prevent scalding (talk about unforeseen consequences). The recirc pumps get the same result--except the line loss goes into the heat envelope of the house--not a bad thing in winter, but less efficient in the summer. The recirc systems deal with the shower/tub too (I think) whereas the small heaters I have seen have been undersink only, typically for the bathroom vanity.

Someone's back of the envelope calculation:

An average home has 125 feet of 3/4 inch pipe. This holds 3.14 gallons of water. If hot water is used 10 times per day, 31 gallons of water is wasted running the faucets/shower to get the hot water. In a year, this equals 11,461 gallons of water. Over twenty-five millions homes waste approximately 300 billion gallons of water annually.

Adding this one--it looks more reputable:

In a 2009 modeling study, researchers estimated that over 10% of all the hot water drawn for showering in a typical single-family home is wasted waiting for hot water to arrive. With Americans taking over 200 million showers a day, that’s a lot of water and energy literally down the drain, of no benefit to anyone. Using EPA estimates of shower water use, that’s about 280 million gallons of hot water wasted each day -- water that has been heated by a water heater, but then allowed to cool as it sits in long pipe runs that are not insulated. This amount of hot water is greater than the total amount of all water used on an average day in the city of Philadelphia, the nation’s fifth-largest. And the energy used to heat this wasted hot water results in annual greenhouse gas emissions equal to that of 1.6 million passenger vehicles. And that’s not even counting the additional water that gets wasted while waiting for hot water to arrive at a lavatory faucet or the kitchen sink.

https://www.nrdc.org/experts/ed-osann/waiting-hot-water

[Dave]

It can take longer to get hot water with a tankless, because the heater has to raise the water temperature first, which takes additional time. The solution to that is a hybrid model that has a small tank kept hot all of the time, plus the on-demand heater. Then you still have the normal irritating wait time for any fixture that's not located close to the water heater.

Retrofitting a recirculating loop is not always possible, particularly with any house that already has a finished basement.