Natural Gas Water Heater

[Max]

Hi, Folks.

It's been a long time since I posted on here which means I've been incredibly lucky or incredibly lazy. You can decide.

I made the decision today that it's time to replace my water heater. It seems to be OK e.g. no leaks, but it's easier to replace the heater than my wife. Allow me to explain. I jumped in the shower this morning and it's cold. Normally our visits to the shower are spread apart by 30-60mins but today my wife was late and I was early which meant back2back showers. Our tank is 40 gallons and the thermostat is set to pretty high (130 degrees I think - I forget the exact number but I know it's nearer the top end of the scale than the bottom end). I don't time my wife in the shower but 40 gallons of HOT water should be enough for more than one person. By the way, there was no other hot water usage such as sinks, washers, etc. This is not the first time I've had a cold shower. The same used to happen when we lived in our previous house. Obviously the problem is not the heater, it's the fact that my wife likes really long, really hot showers. She blames it on her being half asleep. She wouldn't be half asleep if she had to take a cold shower like me but I digress. So my decision was to upgrade to a larger tank, perhaps 75 gallon capacity. I don't actually know if I have a question of if I just came here to vent. Hold on, I have a question!

Q. how much hot water should a typical 40g water heater provide when the temp setting is high?

Q. am I doing my wife an injustice, could it be possible that our water heater is just garbage when it comes to recovering?

Q. can anybody recommend a good brand of water heater? I looked into tankless and I read a few bad things (one of which a post by LazyPup). Is Kenmore a good brand?

Any other general advice is appreciated although as I already said, replacing my wife is not an option. Time has also taught me that asking her to take shorter showers is also not a viable, long-term option.

Cheers, Max

[LazyPup]

Hi Max,,
Having been through the divorce procedure a couple times I completely agree that getting rid of the wife is not an option. Even from the purely practical standpoint getting rid of a wife is far too physically, emotionally and financially cost prohibitive, but on the other hand, usually by the time you settle a divorce you have become quite accustomed to cold showers and you may not even need a water heater.

First let us examine this problem from the mechanical standpoint. Currently the Plumbing Codes limit showers to 2.5gal/min, however a tub is required to have a flow of 4gal/min. In most instances the output from the mixing valve is the same for both the tub and shower port, therefore the shower is limited by the installation of a shower head with a flow restrictor limiting it to 2.5gpm but in the real world we all know that quite often the shower head that came with the mixer is soon replaced with a different style, and one which may not have the appropriate restrictor. Statistically a shower is typically about 4 to 6 minute whereas a long shower may be 10 minutes or more. With a flow rate of between 2.5 & 4 gpm a 10 minute shower would then consume 25 to 40 gallons.

Years ago it was a common practice to operate water heaters at 180degF therefore a typical shower in the 90 to 110deg range was a 50/50 mix of hot and cold water but during the mid 80's there were a number of incidents inwhich people were scalded by the 180degf water so the Plumbing Codes were re-written to limit the hot water distribution temperature to 140degF. In addition, showers were limited to 120degF. In order to meet the new code standards it became common practice to set the water heater to a maximum of 120degF. We instantly began to get complaints from the customers that the water heaters were running out of hot water too fast, and in most cases the solution was to install larger and larger water heaters.

Now let us crunch the numbers a bit.

With the water heater set at 180degF a 100degF shower used a 50/50 mix of hot water & cold water therefore the rate of demand from the water heater was approximately 1/2 the total demand at the shower. This means that while a 10 minute shower consumed between 25 and 40 gallon of water it only consumed 12.5 to 20 gallon of hot water, which was well within the makeup rate of most 40 gallon water heaters. When the water heater temperature was dropped to 120degF a 100degF shower is now a 90% hot / 10% cold mix which means the same 10 minute shower now consumes 18 to 36 gallons of hot water. Now understanding that most water heaters have a first hour recovery rate equal to approximately 85 to 100% of their volume you can easily see why the water heater cannot keep pace with the demand of back to back showers. We must also keep in mind that for every gallon of hot water we pull off the water heater an equal gallon of cold water must enter the tank. Now if the rate of demand per minute is greater than the recovery rate per minute the end result is cold water diluting the hot water in the tank and substantially dropping the temperature of the stored water. Now understanding that the stored water is at 120degF but we desire 100degF at the shower you can easily see how that rate of dilution will quickly drop the available water well below the comfort range of a hot shower.

Obviously you are not going to be able to limit your wifes time in the shower but under normal circumstances this is not a problem because you have a 1/2hour gap between showers which allows the water heater to recover, however in todays quick paced lifestyles often it will not be practical to wait 30 minutes before taking your shower and we both agree that cold showers are not an option so we must find a practical solution. Under these circumstances usually the first thing that comes to mind is a larger water heater but that may not prove to be the best option. Rather than increase the size of the water heater let us consider reducing your total demand for hot water. As you saw in the previous computations with the water heater set at 120degF your shower is consuming about 90% Hot water. The codes prohibit increasing the water temperature in the distribution system, but it does not prevent us from turning the water heater temperature up. The solution here is to install a "Whole House Tempering Valve" on the output of the water heater which would limit the distribution temperature to 120degF while permitting us to turn the water heater up to 160 or 180degF. In this manner as the hot water leaves the tank it goes through the tempering valve where it is blended with cold water to limit the distribution temperature to 120degF. In this manner the water in the Hot water distribution system is now approximately a 50/50 mix of hot and cold, which has now reduced the demand on the tank by 50% while keeping the distribution water at the same temperature. This configuration will also normally keep the demand on the water heater well within the make up range of the heater so you can enjoy a nearly limitless supply of hot water.

With tempering valves typically running in the $40 to $75 range and a simple install they offer a very low tech and relatively inexpensive solution when compared to the alternatives. In fact, installing a tempering valve is a fairly easy DIY solution for those who feel comfortable with soldering copper pipe.

Now in regards to your second question about water heater quality. In essence a water heater is a very low tech piece of equipment and all of them will provide about the same level of performance. In fact, in some instances the only difference between the mid priced "contractor grade" water heater and the high end water heater is the length of the manufacturers warranty, unless of course you are looking at the High end sealed combustion types with forced draft burners.

Comparing quality by warranty can also be very missleading. Lets be honest. Manufacturers hate to pay out money on warranty claims therefore they are usually very careful to limit the maximum warranty period well within the anticipated failure time. While many water heaters offer extended warranties of 6 to 8 years, statistically the average lifespan of even the contractor grade units is 12 years.

Now here is a kicker. In your post you stated that you have a 40gal water heater. Keeping in mind that quite often consumer goods are priced by the overall volume of sales and understanding that a 60gal water heater is currently the primary industry norm in many cases you can buy a 60gal water heater cheaper than you can a 40gal heater.

When choosing a brand name I would prefer to stay with the old time standby's, Rheem, Ruud (which is a division of Rheem), A. O. Smith, Bock or Sears.

As a testimonial, last January I finally replaced my mothers Rheem AUI 40 glass lined natural gas fired water heater which I helped my dad install in 1965. Can you guess what brand name Mother insisted I replace it with?

[Max]

Thanks, LP. A very helpful and detailed post as always. I'm comfortable-ish with soldering copper although I had a near disaster last time when I couldn't get the pipe hot enough to melt the solder. I may let a pro come in this time just so I don't have a heart attack.

Your tempering valve could be the very ticket and I am going to look into that.

Failing that, sounds like you may have a couple of numbers for divorce lawyers.

Thanks, Max

[Max]

I forogt to address this point:

Statistically a shower is typically about 4 to 6 minute whereas a long shower may be 10 minutes or more. With a flow rate of between 2.5 & 4 gpm a 10 minute shower would then consume 25 to 40 gallons.

As I said, I don't time my wife but I believe that her long showers can last close to 30mins. Think that might be the problem?

[SSN596]

The available hot water from a water heater is 70% of gallon capacity at a temp. 20º below the thermostat setting. In other words, a 40 gallon tank set at 130º will deliver 28 gallons of 110º water. You can do the math on how long your showers can be. Setting the thermostat higher of course will help, but will also shorten the life of the tank.

For residential water heater, the recovery rate is too slow to be considered in how many showers you can take. Round numbers, the recovery of a gas water heater is 1 gallon per HOUR per BTU ( 90º rise) . In other words, if your cold water is 50º, a 40,000 BTU burner will heat 40 gallons per hour to 140º, or 0.66 gallons per minute, so the shower is using water faster than you can heat it up. This is why the 70% rule is the number which applies to this discussion.

Another rating is "First Hour Delivery". This is the sum of the 70% number and the recovery rate. SO, a good 40 gallon tank with a 40K btu burner will have a first hour delivery of (40 x .7) + 40 = 68 gallons first hour. Note that this does NOT mean 68 gallons in 15 minutes. Once you use the initial delivery of 70% then all you have available is the recovery rate water, 0.66 GPM.


If any one is still awake, here are some more figures for you:

Mix rate, assuming 50º cold coming in:

thermostat at 120,shower at 110 mix is 86% hot
thermostat at 130,shower at 110 mix is 75%
thermostat at 140,shower at 110 mix ix 67%