Home water heater... tankless?

[shawn]

This is one of those deals where Shawn has made his mind up for his situation and is so convinced that hes right he cant fathom someone else having a different preference. I love the dude like a brother but its one of his few flaws.

Not the case at all. It sounds to me like you didn't actually read my post.

Clay posted up a question, provided no backup information to frame the problem, then expected us to provide relevant answers.

If you want to talk to somebody who's made up his mind on tankless, there's always @CasterTroy

 

[shawn]

On this note, I've often wondered if having a small PID controller to adjust the water set temp (switching between "pretty warm" and "really hot" for the time of day would be worthwhile. E.g. if all the action when you're concerned about running out happens at the same time, why not do a small increase then, then let it back off for the rest of the day. For us, showers are the only time we use a lot at once. Everything else is small doses or doesn't really have to be THAT hot.

No, because it takes a lot of energy to bring the tank up to temp, then very little to maintain that temperature for a long time. If your power goes out today, you'll still have hot water on Sunday.

 

[shawn]

Here is what I can tell you. We switched from electric to gas in a tanked heater, 80 gallons in a climate controlled basement btw, and you can get 1 shower about 35 minutes long and shes cold.
My teenage daughter confirms this nightly. We have the temp set at 8 notches out of 10.

Something is wrong with your water heater. A 74 gallon AO Smith will provide 143 gallons of hot water in the first hour at a 70F temperature rise (130F tank temperature).

 

[Ron]

Something is wrong with your water heater. A 74 gallon AO Smith will provide 143 gallons of hot water in the first hour at a 70F temperature rise (130F tank temperature).

What assumption are you using for flow and fill rate?
Is it because we dont have low flow shower heads?
What about piping loss/length does that play a factor?
What about input temp? Our water here is cold coming in...Ive never measured it but out the tap its as cold as out the fridge dispenser. Its kind of a running joke.

Im not water heater guru. Im just telling you our new water heater (its a State not an AO Smith) can be ran cold

 

[shawn]

What assumption are you sing for flow and fill rate?
Is it because we dont have low flow shower heads?
What about piping loss/length does that play a factor?
What about input temp? Our water here is cold coming in...Ive never measured it but out the tap its as cold as out the fridge dispenser. Its kind of a running joke.

Im not water heater guru. Im just telling you our new water heater (its a State not an AO Smith) can be ran cold

It's in the post. If you assume you're heating the water 70F, you can get 143 gallons in the first hour. There are 52 usable gallons in the water heater before the temp falls off, and the WH is capable of generating 91 gallons per hour at a delta T of 70F. I think you have a well, so your groundwater temp should be in the neighborhood of 50-60F year-round. If it's actually less than 52F, I have no idea how or why that could be happening.

Pipe length and flow rate don't really factor into it, except to the point when you outrun the 90 gallons/hr number. I'm also assuming you're using 100% hot water, which biases the math against the water heater. If your setpoint is 130F, 140F, or even 160F, you're using proportionally less water from the WH.

I'm not familiar with State, but it could be that you have some bullshit tiny-ass 30k BTU burner, so the first hour capacity is only like 80 gallons. If that's the case, somebody selected a water heater that doesn't meet the design requirements.

The point is, it's a simple math problem. If you know how many GPM you need simultaneously, how many gallons of water you need over any 2hr span, what the worst-case inlet temperature is, you can do the math and figure out exactly what's required (tank or tankless), and then do the TCO to figure out the best value. Every time one of these threads comes up, there's somebody that comes along and says "I've got a 100 gallon jacuzzi tub in my bathroom, there's no way I could fill that with a tank water heater", but it's just not true.

 

[BigClay]

Clay posted up a question, provided no backup information to frame the problem, then expected us to provide relevant answers.

Pretty much!

I was really looking for “I went tankless and never looked back because of...” or “fawk a tankless it sucks becasue...”

I have no idea about flow rates and insulation regression or how a flux capacitor on a Delorean works. I just want some experience with those that have had or used both and their thoughts; preferably before my 29 year old unit decided to spill its guts all over my basement.

 

[obullfish]

Can two showers run at the same time and have enough hot water?

Yes. Our master shower has multiple heads that are always on and we also have enough hot water output to be using a guest bathroom shower at the same time. Using a Rinnai tankless on propane for going on 12 years with ZERO regrets.

Old house had a natural gas regular tank water heater and we ran out of hot water occasionally.

 

[Ron]

There are 52 usable gallons in the water heater before the temp falls off,

Aside from all the other stuff this is where your calculations fail.
The minute you crack a hot water valve and hot water starts to flow as any of that 52 gallons starts to flow out its replaced by an equal amount of water at some F.
If the whole tank is happy at 150F (or pick any other set point) the instant water starts being replaced the entire column temp drops, from 150F to 149.9 F, then 149.9 is replaced by more 50 and its 149.8 etc...its a exponential curve to a point of taper level.

You dont have 52 gallons before temp fall off...

 

[CasterTroy]

If you want to talk to somebody who's made up his mind on tankless, there's always @CasterTroy

 

[shawn]

You dont have 52 gallons before temp fall off...

If that were true, you'd have to constantly adjust the shower temperature.

On the other hand, last year our water heater burned up the bottom element. It would give about 10 minutes of hot shower, about 5 minutes of decreasing temperature shower, then fucking cold. This is with an old-school two valve gasket-and-seat setup. The hot water stays at the top of the tank. If the top element had been the one to crap out, we probably would have had longer showers up front, but shitty recovery time. Convection would have taken care of getting the tank to a uniform temperature.

 

[obullfish]

See what you’ve started @BigClay

 

[CasterTroy]

Aside from all the other stuff this is where your calculations fail.

You see how shawn keeps mentioning 1st hour?
This is where the mixing curve starts changing the recovery rate. That's WHY you have 1st hr vs every hour recovery afterwards

Im not water heater guru

clearly

Even though Shawn likes to allude to the fact that I'm a hard headed dumbass who will never change their mind about something , I will always listen to a valid argument and have an open mind.

I do believe instantaneous has their place. However in Forsyth county, due to the fact that the county water has such a harsh ph to foster scale at a much faster rate (because all of the infrastructure piping along Winston-Salem is failing) I never spec and instantaneous water heater for our area because no one bothers to do the annual flush and maintain the heat exchanger properly and typical failure will happen after 5 years.
I personally have a state 40 gallon gas water heater, For the last 11 years and it has survived 3 teenagers, a 100 gallon Jacuzzi tub and a wife that takes a 20 minute shower before me in the morning and a bath every single night while the kids are usually showering. My set point is at 140ﾟ And I can count one hand the number of times we have ever encountered any kind of hot water deficit, and that was when my wife was taking a bath at night we were washing towels in hot water, the dishwasher was going and my daughter was taking a shower upstairs.
Keep in mind my son used to take 30 minute showers and both of my daughters wash their hair and usually will take a bath and shave their legs, and THEN a shower immediately after around the same time my wife takes her evening bath.

I personally will never own an instantaneous water heater because of so many experiences with them not working properly, but also will never have a VRF system in my home. Not because they aren't wonderfully efficient and are the absolute most perfect way to individually cool and heat different rooms, but because they are so complex and when one fails you cannot run up to ACR and find a replacement part any day of the week. It's along those same lines why I continue to support tank water heaters.

YMMV Consult a doctor if rash continues, do not use happy fun ball in States that do not allow its packaging. Happy fun ball originated from a space rock that fell from a distant planet.

 

[CasterTroy]

My old 50 gallon water heater rusted from the inside out and ruined my floors.

How often did you replace the anode rods?

 

[336wheeler]

The water heater failed during my 30-day due diligence period of buying the home and the seller gave me a $3k credit to replace the carpet. So I spent it on hardwoods and did the work myself.

I’m sure they never got replaced by the previous owner.

 

[BigClay]

How often did you replace the anode rods?

See, something else I didn’t know you had to replace.


Ok, so far this is what I have gathered: I need a big @ss pot and good hot fire to put the pot on, make my own hot water and be done with it

 

[Chris_Keziah]

See, something else I didn’t know you had to replace.


Ok, so far this is what I have gathered: I need a big @ss pot and good hot fire to put the pot on, make my own hot water and be done with it

Next time just pick up the phone and call @CasterTroy he knows a thing or two about a thing

 

[shawn]

You see how shawn keeps mentioning 1st hour?
This is where the mixing curve starts changing the recovery rate. That's WHY you have 1st hr vs every hour recovery afterwards

Yup, and why you multiply the tank capacity by .7 to get the actual usable capacity before you start getting into the other 30% of diluted water at the bottom of the tank.

 

[Caver Dave]

Yup, and why you multiply the tank capacity by .7 to get the actual usable capacity before you start getting into the other 30% of diluted water at the bottom of the tank.

OK, let's reverse the train... getting ready to purchase an ELECTRIC tanked water heater for the step-son's house and want to make damn sure he gets not_a_fawking_second_more than 30mins of shower before ice starts forming on his balls.

What size (capacity) and 1st hour recovery rate do I need?

 

[kaiser715]

Another reason we went tankless....we wanted LP hot water, not electric...since we hit a layer of leverite rock (as in leave'er right there) when digging what was to be a walkout crawl/basement, I ended up with a shorter than planned, but tall crawlspace. Barely standing room on the high side, but not enough headroom for a "shorty" gas tank (still over 4'), considering stack, clearance to combustables, etc. Tankless was the only way to have LP hot water, without paying big (bigger) money to move rocks. Or put it on the main floor.

 

[Silverado_Express]

Rinnai tankless natural gas exterior model (no venting needed) and love it.
Pros: Never run out of water, saved a little on power bill every month but obviously will take awhile to offset initial cost, and one of the best things is I plumbed in hose bibs at inlet and outlet of unit on side of house not just to flush it but I hook my pressure washer to the hot side and essentially make a steam genie.

Cons: initial cost, depending on where you put it determines how long it takes to get hot water. For instance mine is on back of house but kitchen is on front. Washing your hands in the sink requires a little more time to wait on hot water since my old tank unit was in crawl space under kitchen, and my dishwasher doesn't shut off but if I use it I will usually help purge the hot water up to it by running the sink.

If you need the capacity, it's a easy decision in my mind

 

[RatLabGuy]

How often did you replace the anode rods?

Bingo.

Slightly off topic, but his is a good time to remind people - replace those damn rods.

 

[jeepinmatt]

Aside from all the other stuff this is where your calculations fail.
The minute you crack a hot water valve and hot water starts to flow as any of that 52 gallons starts to flow out its replaced by an equal amount of water at some F.
If the whole tank is happy at 150F (or pick any other set point) the instant water starts being replaced the entire column temp drops, from 150F to 149.9 F, then 149.9 is replaced by more 50 and its 149.8 etc...its a exponential curve to a point of taper level.

You dont have 52 gallons before temp fall off...

You're arguing a half truth. Someone earlier mentioned flow rate did not matter, which is the absolute opposite of true. It has everything to do with flow rate. If your flow rate is equal to or less than the rate at which you can heat the water, you will have an "infinite" supply of hot water. However, if you have a flow rate that is higher than the heat input rate, the temp will drop until the temp matches the heat input rate and then it will equalize. A tankless unit is just a bigger heater that can keep up with or exceed the expected flow rate. The tank style uses the big thermal mass as a buffer to conserve energy.

 

[Fabrik8]

A tankless unit is just a bigger heater that can keep up with or exceed the expected flow rate. The tank style uses the big thermal mass as a buffer to conserve energy.

The thermal buffer doesn't conserve energy though, it just stores energy. It still takes a specific amount of thermal energy to change the temp of water, regardless of how fast you do it. You're not saving energy by heating the water at a lower rate with a smaller heater on a tanked unit.

 

[UTfball68]

So I see in typical NC4X4 fashion, a hot water tank is best, unless a tankless is. There are a ton of factors that 98% of people don’t consider when buying that NC4X4 guys in the biz can’t agree on either. And I’m just over here with dual 50 gallon tanks on natural gas and come to terms with the fact I’m going to take a cold shower after a few loads of laundry, the dishwasher has run, the two girls get a bath and the wife takes a bath in the jacuzzi tub (sometimes refilled if it’s been a particularly rough day)...or I just change the time of day I take a shower.

 

[shawn]

You're arguing a half truth. Someone earlier mentioned flow rate did not matter, which is the absolute opposite of true. It has everything to do with flow rate. If your flow rate is equal to or less than the rate at which you can heat the water, you will have an "infinite" supply of hot water. However, if you have a flow rate that is higher than the heat input rate, the temp will drop until the temp

The extent to which that matters depends on whether you're talking tank or tankless, and what the duration is. With a tank system, you can calculate how much hot water the tank can provide at a specific temperature delta for the first hour. If you exceed that capacity, you run out of hot water. It doesn't matter what the flow rate is, once it's gone it's gone.

In a tankless system, its all about flow rate. If you have two 2.5gpm shower heads or two 1.8s, the size of the water heater has to change. If the Delta T gets bigger, the WH has to get bigger. If you exceed its capacity to provide X gpm, the temperature falls off until it equalizes with the burner capacity.