Tankless Water Heaters?

I'm due for a water heater. My existing tanked version has a pin hole leak. I'm considering a tankless WH. I don't have gas service so for a gas WH I would need to run lines and acquire a larger tank. I currently run a gas range off of 20lb  bottles. 

While doing research, I came across a couple of electric tankless water heater. A 24KW to 27KW looks like it would handle my needs. Since the house panel is right next to the water heater, it would be a fairly simple job to run the required 3 - 40 amp circuits to the WH. 

Thoughts?

In reply to Toyman01 :

I'm not a fan at all. I installed an under-sink Bosch unit in our downstairs bathroom when we remodeled our place in IL. The first one melted the cpvc pipe when it was first turned on, even though it was installed correctly. I exchanged it for another one, which fortunately didn't have that problem, but there is no "warm" water, regardless of how you adjust it. It's either ice cold, or scalding hot.

Our new place has a higher-end unit(I'd have to check brand/size) installed in the master bath. It sucks. Any slight variations in water pressure - even from neighbors flushing their toilet - cause water temps to vary pretty widely. It has a 2-stage heating element, so you need to first turn the hot water all the way up, then try to balance the temp with the cold water. Also, we have a whirlpool tub next to the shower that's completely useless, but that's because the water doesn't get hot enough...even though it's adjacent to the shower and fed from the same line. If I had a place to install a normal gas water heater - or I ever get really ambitious and rip all the electric and plumbing out of this place & start over - I'd replace this damn tankless unit in a heartbeat.

FWIW for the upstairs in IL I went with an AO Smith conventional gas water heater, but one that's capable of keeping up with steady use. For a family of 6 we needed it, and it worked flawlessly. 

My mother just redid her house and had 2 smaller TWHs installed instead of one large traditional water heater. She has been complaining of exactly the same problems as Pete.

I just checked - ours here in MS is a "PowerStar" by BBT fwiw...which after a bit of googling, appear to be made by Bosch too.

We switched  to tankless about eight years ago. No issues except it takes longer for heated water to reach the outlets.  Just have to be patient.  We're on a well so no issue with wasting water or paying a water bill. 

I'm looking at whole house tankless units. It looks like an electric unit for my house would draw about 27kw or 112 amps. In SC that would run two showers and a sink at the same time. It's looking like sizing is extremely important. Too big and it goes hot cold because of lack of flow. Too small and it just puts out lukewarm water. 

The reviews are all over the place for them. Even the gas units seem to be pretty polarizing. People either love them or hate them.

All the professional reviews are firmly in favor of tankless, but I think that's due to the amount of money they make installing them. 

More research is needed. 

In-laws have had one for decades without any problems. We had two that were nothing but trouble. Hard water and all but I cleaned it once a year. Maybe that wasn't enough. They are nice when they are working properly but ours were high maintenance

I lived in an apartment with an electric whole-house water heater.  The building had industrial Delta-Hi power and it was an impressive unit.  It was great, but the duty cycle wasn't up to the needs of two people in an apartment.  You'd take a shower and get about 6 minutes before it said "screw this, I quit."

Also lived in one with a gas version.  The way they extract the maximum heat from the exchanger usually requires a good bit of restriction.  When you have restriction to flow in on circuit, that is where you get the temp fluctuations when the toilet flushes or the washer kicks on.  If you have equal flow in both hot and cold, changing supply pressure won't affect anything in theory.  If you have a lot of restriction in one side, set your shower to a certain temp, then change the pressure, prepare for bigger flow loss in the restricted side than the non-restricted side.

I looked into them for my new house and decided to skip it.  My current one is electric, but my house does have gas.  I figure I'll run a gas line to a new gas water heater and a new gas cook stove and that frees up two 240v spaces in the panel; one of which will repower the garage.

We have a gas one, whole house.  Now that we've had it for 3 years, I couldn't imagine not having one.  We absolutely love it.  We don't have any issues getting hot water quickly, it takes about the same amount of time as a tank heater did.  But the supply is endless.  With 3 kids, it's very valuable.  We also have a dual master shower...full body shower units on each side of the shower enclosure.  We can run both sides for a long time, no problems...just sayin'.   We can do laundry and run the dishwasher at the same time if needed (we try not to, but we can). 

If they have a downside, we haven't come across it.  They are phenomenal, I highly recommend it.

Toyman01 said:

All the professional reviews are firmly in favor of tankless, but I think that's due to the amount of money they make installing them. 

 

You are correct in that assumption. 

Sine_Qua_Non said:

Toyman01 said:

All the professional reviews are firmly in favor of tankless, but I think that's due to the amount of money they make installing them. 

 

You are correct in that assumption. 

Keep in mind that for a gas TWH, you need different exhaust plumbing, larger air intake, larger gas supply line and ideally a flush valve setup for annual backflushing.  This all adds up, but some of these items are eliminated with an electric unit.  

Distance from the TWH to the water outlet is the biggest factor in how long it takes for hot water to reach you.  Remember, you can't use a recirc pump on a tankless system.  

My parents have one and with the exception of it taking a little longer to get hot water it is awesome. I am doing one on our house when the time comes.

We've had a Rennai gas tankless whole-house heater for about 10 years now.  I love it; it works great.  It was especially good when we had 2 teenagers and 2 adults in the house - it will basically let you take an infinite shower.

Operationally they take a little getting used to - you need to get their attention, and keep their attention, when you want hot water.  But overall, I have zero complaints.

When I build my dream house I'm putting in a 6 gallon water heater and a tankless. Immediate hot water, endless supply. 

Just doing a bit of math before I answer.

Federal rules on a water saving shower: 2.5 gallons per minute max

Assume the water is brought in at 55 degrees F and heated to 100.

First step, convert numbers to metric since it's rated at 27 kW.

2.5 gallons per minute = 158 g/s

45 degrees F delta = 25 degrees C difference

158 g / s * 25 degrees C * 4.184 Joules / degree = 16.5 kW.

Assuming the system is 90% efficient, the 27 watt unit is going to be at about 2/3 capacity to run a shower, and the 24 watt unit is going to be at 76% capacity. It's going to get really cold if somebody turns on the washing machine by mistake while you're in the shower.

I just completed converting my house to gas from electric.  I looked at the gas tankless, but couldn't make the numbers work once the federal tax credit expired, the pay back time was close to 10 years, so I went with a 9-yr 40k BTU tank type water heater.  I didn't even look at the electric, way too much draw and operating cost.  We use gas tankless quite a bit here at work and for the most part they are reliable and work well.  Sizing is critical, and look at the temp rise for about 70 degrees, because that is probably what it will be close to in the winter.  As the delta gets greater, you will get less hot water flow, I just don't think that electric will be able to keep up for more than a hand washing sink.  The other thing that led me to a gas tank style was hot water in a power outage.  With a tankless you will not have hot water when the power is out, may not be important where you are at, but our power typically goes out in the winter, so having a nice hot shower is handy.

In reply to SlimShady218 :

I don’t think you considered everything.  Tankless can usually be put close to high use areas if not in high use areas.  That means real short runs to where things are used.  

So you don’t need to run the hot water as far.  Less wasted water waiting for hot.  

Even though I live in the land of 10,000 lakes

( actually over 15,000)  and I live right on one of those lakes so my lawn sprinkling comes right out of the lake and doesn’t go on the water bill, my water bill is the most expensive utility bill we pay!  Yes! Includes natural gas in the 30 below weather.  

So reducing water usage is important. Tankless is a few seconds waiting for hot water, when I run from my two water tanks it’s a couple of minutes. 

Threadjack:

What's the hive's opinion on getting a small one to put in-line AFTER the heat exchanger water heater that runs the whole house for just one or two shower(s)?  I don't care about dishwasher, washing machine, faucets, etc.

I've got a herd of kids, and I've noticed that by the end of bath night, the water heater can't keep up unless switched into electric-only mode (no heat exchanger).  I've thought about getting a small tankless water heater and putting it in-line for the two showers only.  That way, if the temperature starts to drop, it can kick that on and maintain an infinite shower for when all of the kids grow up and need to take a shower every day.   For those doing math, I'd have it kick in somewhere around 105-110°F so it shouldn't get too cold water as a source.

I haven't looked into it yet myself, so I'm just checking to see if that's an option since this thread popped up.

In reply to frenchyd :

I wasn't referring to water usage,the water usage difference is negligible in my instance, I was referring to energy savings vs. cost to purchase and install the tankless.  I would have swapped in a whole house unit in place of the existing 50 gal Electric, so it would have been on one end of the house, while the back bathroom is on the opposite end of the house.  The tankless are very efficient (at least gas) vs. a tanked type, but the difference in purchase and installation cost pushed it past the pay back time frame that I was comfortable with.  There is also the "cold water sandwich issue" that you experience during some operating conditions.  It sounds like you have a circulation pump installed with your unit, that was an upgrade I considered, but again, greater installation costs and one more item to maintain.  The tankless aren't maintenance free and are more adversely effected by calcium and scale in the water supply, so the heat exchangers need to flushed on a regular basis and the flush kits are usually sold as an added accessory.  The bottom line for me was after I looked at everything it just didn't make financial sense for me to make the jump to the tankless.  That being said, I am beginning design on a new house in the next few weeks and a gas tankless is on the list of "wants."   

I was always under the impression that tankless was better in a more modular platform than as a one unit replacement. Meaning several small units near where the water will be used instead of one big one. 

​​​​​​when I still thought I was going to be able to build a new house, my plan was one in each of the bathrooms and one in the kitchen. All as close to their usage point as possible. I briefly thought about using a tankless system to run an in floor heating system, but without free gas, that's a huge money sink for little reward. 

I've never owned one and never knowingly used one, but when they were first getting popular my dad had looked into setting up an installation company briefly. 

mtn said:

When I build my dream house I'm putting in a 6 gallon water heater and a tankless. Immediate hot water, endless supply.

Check out the HTP crossover units. They are essentially what you described in one package. They have a wall mount unit or one that sits on the floor like a traditional tank water heater. Pretty neat unit. I believe the wall mount units even have a built in recirculation pump so you have instant hot water at the faucet

old_ said:

mtn said:

When I build my dream house I'm putting in a 6 gallon water heater and a tankless. Immediate hot water, endless supply.

 

 I believe the wall mount units even have a built in recirculation pump so you have instant hot water at the faucet

Just a note of clarification - that requires the plumbing be looped to each individual hot water faucet, effectively adding 30% or more supply piping to your project.  It also requires either a house being built new, or a PITA retrofit of the return lines.

MadScientistMatt said:

Just doing a bit of math before I answer.

Federal rules on a water saving shower: 2.5 gallons per minute max

Assume the water is brought in at 55 degrees F and heated to 100.

First step, convert numbers to metric since it's rated at 27 kW.

2.5 gallons per minute = 158 g/s

45 degrees F delta = 25 degrees C difference

158 g / s * 25 degrees C * 4.184 Joules / degree = 16.5 kW.

Assuming the system is 90% efficient, the 27 watt unit is going to be at about 2/3 capacity to run a shower, and the 24 watt unit is going to be at 76% capacity. It's going to get really cold if somebody turns on the washing machine by mistake while you're in the shower.

 

Good points to consider.

All of the electric units I've looked at are rated 99% efficient. Inlet water temp is right at 60 degrees during the winter and well over 70 during the summer. The one I'm looking at is rated at 3.84 GPM with a 57 degree inlet and a 105 degree outlet temp. I flow tested my showers and sinks yesterday and they are all 2 GPM. We would have to be careful during the winter to not over draw the system, but our last house had a 30 gal water heater for 6 people, so we are pretty used to being gentle with hot water usage. Even close washing is usually done with cold only. I'm also not above putting flow limiters on the sinks. During the summer months, we would have 6+ GPM of hot water and that should be a gracious plenty. 

As to costs.

A tanked water heater would set me back about $450 installed by yours truly. 

The tankless is going to cost about $600, including the service valves and the 3 - 40 amp circuits. Also installed by yours truly. 

So about $150 extra for tankless. 

Going by the "industry" calculations, I should break even in under 3 years. 

Another interesting tidbit. At least three of the manufacturers of electric units use the exact same guts.

Rheem, EcoSmart, and Eemax all look just like this under the cover.