Thread: double water heater?

Newer inspector here, can someone explain the purpose of this? This is the first time I have ever seen this set up.
It appears hot water is feeding into another water heater already hot? I can guess why, but is this concidered code, and can this set up damage one of the units?

chris

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You will get different opinions from different sources, however the only industry source I am aware of which takes a position on this is AO Smith, which recommends against series piping.

It's one way to increase the volume of hot water. The other way is two tanks in parallel.

BTW, the electrical supply cables should be in flexible conduit.

Thanks,
I printed that out to keep. parallel seems to make more sence here.

When two water heaters are plumbed in series the upstream unit works harder than the downstream unit because the upstream water heater does most of the water heating while the downstream water heater acts mostly as a hot water storage tank. Therefore the upstream water heater will most likely wear out faster than the downstreak water heater.

When two water heaters are plumbed in parallel the two units share the water heating load equally and will probably wear out about the same time.

If your hot water needs exceed the capacity of one water heater it would be more economical to install one large water heater rather than two smaller water heaters. With one large water heater (rather than two smaller water heaters) the installation cost will be less and standby losses will be less.

Here is a possible reason for this type of installation.
Two heaters but one is primary and consistently on.
The second is turned on only when there will be a need such as extra house guests.
Maintaining 30 gal temp is cheaper than 60 gal temp when you only need 30 gal for normal day to day use.

Technical Bulletin 64 from A. O. Smith is very interesting. Thanks for the link.

It states "Piping in series can cause the first heater to fail sooner than the second. The reason this happens is you are using the full capacity of the first heater and only upon an increased demand, is the second heater cycled on. This causes the first heater to be used more than the second, and used to its fullest capacity."

Of course. As Bruce pointed out, the first is doing the bulk of the work as if it stood alone.

It goes on to say, "This can cause the first heater to condensate and corrode."

Again, of course. That is normally what happens when gas fired water heaters work.

The bulletin then states, "Piping in parallel allows you to use both heaters equally. It allows the system to act as one heater rather than independent."

This is true but does one really WANT both to operate at the same time? Not in an energy efficiency scenario which has typically been the reason for installing two water heaters instead of just one larger unit.

An energy efficient system can be installed in several ways using two water heaters or "tanks" if you will. All are based on a series piping configuration.

1) Water supply enters tank 1, is heated and passed along to tank 2 for storage and draw by the fixtures. When tank 2 is drawn down it draws hot water from tank 1 so it should not have to fire. When tank 1 is drawn down enough, it fires. If demand continues, tank 2 may also fire but at least, not for very long.

2) Water supply enters a holding tank which may or may not have the burner operational or even have a burner for that matter. Water is passed along to tank 2 which is heated normally. When no demand is called for, the cold water sitting for extended periods in tank 1 is simply heated, or more correctly, "tempered" by surrounding room air before being drawn into tank 2. In this case the cold water temp can be raised many degrees while sitting in tank 1 before gas is needed to heat it to the owner set temp in tank 2. Tremendous energy savings can be realized with this method.

Water heaters are typically installed in the garage in my area where summer temps in the space can easily reach and stay at the high 90's to low 100's. This can raise the temp of the stored water considerably before it has to be heated using NG in tank 2. Even in moderate climates the water supply temp is normally in the 50 degree range and by allowing it to temper, can be raised considerably before heating thereby saving energy.

A. O. Smith advises parallel piping to evenly wear the water heaters, but then they do have an agenda...they sell them.

Thanks, Bob. Tempering makes a lot of sense. You could have two functioning tanks in series, but turn the first one off, or run it at a low temp.

Parallel setups have valves so you can shut one tank off, but that requires some planning when guests arrive. When you activate a cold tank, cold water will be mixing with the warm for a little while.

I saw this setup recently. An electric furnace with a wood burner on the side, water heater coil in the wood burner, in series with an electric water heater. We have relatively cheap hydroelectric here.
The sellers have disconnected the wood heated tank, wrong. The water could be warming up just being in the tall tank beside the furnace.
Also, the coil should have water in it when the wood furnace is used, I think. Anyway, my clients got happy when they realized what they were buying.

All of that about "one unit wearing out before the other" because it is doing the heating and the other is not ??????

YEAAAAAAAAAAH

That is one of the ideas behind it. One comes on just as it was a stand alone and does not work any harder than a stand alone so it will have a normal life expectancy.

The second does not come on as much so it does not work as hard and will last longer

Yeaaaaahhhhhh

This set up is wise and I always recomend it. Why have both water heaters firing when only a little water is used from both tanks. That defeats the purpose of only having two water heaters. The idea is for longevity of the second tank and economics of only having one heater kick on when there is little water use but have the stand by for double the water usage before it runs dry. I know a lot of families this work out great for. They have the back up when family is in and only use the one tank firing when the family and friends are not over.

I can also vouch for lower water heating bills as I ask countless folks over the years about the economics.

This was also true with myself in my last home in florida. Better economics and greater storage capacioty when the kids were back and forth from college.

Yeah, John, the set you up pictured is almost better than having two water heaters because there is no insulation on the tempering tankso it'll absorb ambient temps faster. Ya just have to be careful of possible condensation forming on uninsulated surfaces that may run down and damage something.

Chris the other solution is to go tankless. these are becoming more popular and use less space. I have 2 different ones installed in my houses and have see others installed too. I have never run outta hot water but don't have to worry about storing hot water and not using it either. their claim to fame is less space needed and no need to store heated water when not needed. They are a supply on demand unit which when needed can supply 3-4 different appliances. but depends on the size of them just like a hot water tank. there are electric and gas units depending on the application. also no need to worry about adjusting them when you have more company. the only downside to them is longer showers cause you don't run outta hot water and have to get out lol. But I can live with that. the extra space is nice too

I have this set-up in my own garage using two, 50 gallon water heaters. The top water heater (first in line) is the "Master", the bottom one (2nd in water line) is the "Slave" because it works under the control of the top water heater's thermostat.

When the top thermostat is satisfied. It transfers power to the lower thermostat, but also because cold water comes into the heater from the bottom first the lower element does the most of the work. The upper only comes on when you've had a long draw on hot water and the upper thermostat senses cold water. It actually works very well in saving energy.

Originally Posted by Bill Hetner

Chris the other solution is to go tankless. these are becoming more popular and use less space. I have 2 different ones installed in my houses and have see others installed too. I have never run outta hot water but don't have to worry about storing hot water and not using it either. their claim to fame is less space needed and no need to store heated water when not needed. They are a supply on demand unit which when needed can supply 3-4 different appliances. but depends on the size of them just like a hot water tank. there are electric and gas units depending on the application. also no need to worry about adjusting them when you have more company. the only downside to them is longer showers cause you don't run outta hot water and have to get out lol. But I can live with that. the extra space is nice too

Bill,
Have you performed a cost to benefit analysis over the projected life span for the equipment?
What is your annualized cost including maintenance and equipment?
What is your fuel type and cost?

If the parallel setup is used, how would we determine that water is flowing at the same rate through both water heaters? Without a flow meter one water heater could end up as a holding tank if there is a small pressure difference (more fittings, longer length pipe, etc).
Toughts?

- Josh

A quality installation will have equal arms on both the inlet and outlet ahead of the tees to ensure equal water distribution. To test, simply feel the line in similar locations for temperature change when drawing water from cold lines.

Originally Posted by joshua humphrey

If the parallel setup is used, how would we determine that water is flowing at the same rate through both water heaters? Without a flow meter one water heater could end up as a holding tank if there is a small pressure difference (more fittings, longer length pipe, etc).
Thoughts?

- Josh

Hello, Josh. The pressure at the tanks won't be much different. The pipe diameters should be equal. Yes, one tank will fail first. You could place bets on which one it would be?
Here's a pic of a goofy parallel tank setup. There was no room in the crawl for a normal water heater. I would have them in series, but I'm not a plumber.

I knew a Chris Gallo from R-MA in Front Royal. Same guy?

They should be installed in parallel with heat trap (unless its build into WH and mixing valve)

Hi Gary, in regards to your questions. the research I have done is based on research on the net and talking to people who have had them. both units I have are gas fired. effiency is in the high end of around 98% condensing units. the Units I have are Navien and Rinnia. I have the Navien here in Vancouver Canada and the Rinnia in Edmonton Ab Canada. The Navien I bought outright at about $3500. there were also goverment rebates for them provinally and federally. the only maintence we have had to do on it was clean the air fliter on it as it was clogged after one year. The one in Edmonton is a rental from Sears and cost me $70 for a permit and about $35 a month with a buy out plan. No problems with it so far but if there are it's sear's problem as it is a rental. As to performance no complains as no one runs outta hot water. As to gas cost they are going to be lower if water use is the same but higher cause you don't run outta hot water. My tenant in Edmonton did complain about the cost, but he has a family of 4 and they use lots of hot water. when I suggested they use less hot water he declined and decided it was worth it.
As for how long they last I got no real answers from people in person but on the net they claim they last just as long if not longer than tanks. it really varies from place to place and use and water conditions.
I look at it this way. If my tenant downstairs has a shower or doing something with hot water and I need to shower I am not running outta hot water. with a tank generally it's one shower then you have to wait 10-30 minutes. Yes at first you pay more for the tankless but the performance in the long run is well worth it. You have higher efficenty and when not in use is not keeping any water warm.
-:- Navien America -:- and Tankless Water Heater Buyer's Guide and Dealer Search from Rinnai | Rinnai America these are both gas but the electric are very small units compared to them. both are smaller and mount on the wall saving space
I grew up like most with a tank and hated running out of hot water. In Edmonton I have a jet tub and filled it half way listen to 2 songs on radio and filled it rest of the way. now with tankless there I could shower then soak and still not run outta hot water. it is sweet, well for my tenants now lol. But still worth it. I have one here too and love it everytime I use it with no worries of running out of hot water.
Do your own research as to what your needs are but when a tank is ready to be replaced consider it a worth while option. imo

Originally Posted by Eric Barker

I knew a Chris Gallo from R-MA in Front Royal. Same guy?

Not me, Born in CT and moved to MD in 83'.

regards to cost of gas:

Fortis BC – gas
Delivery
Basic Charge 11.84
Delivery 3.207 per GJ
Commodity charges
Midstream – 1.349 per GJ
Cost of Gas – 4.568 per GJ
Taxes and fees
Carbon Tax $0.9932 per GJ
HST – 5% of Delivery Charges, Commodity Charges and Carbon Tax
(One GJ {gigajoule} is roughly the amount of energy needed to heat a typical house for 1 day during cold winter weather. You pay for the gas you consume, measured in gigajoules.)(in Canada we like to tax our taxes too)

Midstream commodity charges are charges they pay other companies who store, transport and help them manage the gas they deliver.

Everywhere costs are different but when you need it your going to have to pay for it regardless.

Zibby there are pros and cons to every application. In parrellel you can take one out of the system for maintence in series you going to have one doing most of the work and is going to wear out sooner. really depends on the application and what the owner wants and likes. every application and need is different but limited to what is available.

Bill ,
Thanks for the info.
Carbon tax is interesting.
Have not had the time to do a spread sheet to see a comparison. Maybe soon.
Years ago sold Hi E furnaces and when you did the math there was not much savings. But that all depends on the cost of fuel.

Like spending an extra $20K for a car to save fuel. $20K buys a lot of fuel.

I have 2 in series. The original is propane fired. The newer one in front is electric. The cost of propane (an unregulated industry) is so high that it was worth it to buy the new unit, install it and use the propane for back-up.
jlmathis

Originally Posted by Garry Sorrells

Bill,
Have you performed a cost to benefit analysis over the projected life span for the equipment?
What is your annualized cost including maintenance and equipment?
What is your fuel type and cost?

I am not a big fan of low water volume, high BTU tankless water heaters. I worked in the commercial field for years and some of the work included maintaining hot water heaters and boilers. The biggest problems came from scaling due to bad water chemistry. The buildings on well water were worse than the ones on city water but descaling of the water paths was a routine maintenance item on both systems. The more scaling the lower the efficiency. The tankless heaters on the market have small water paths so they can get scaled up pretty quickly. I recommend to clients that if they need more hot water they should add additional tank heaters.

James no offence but I have had the tank system and didn't want to go the way of a second tank and more power usage to supply my water needs. Also I don't have the room for a second tank. Having used tanks most of my life and regularly running outta hot water an endless supply is sweet. Every thing in life has it's pro's and cons. as for me I wanted to try something new and it is working great for me. I am on city water for both. As for scalding that can happen with a tank set too high too. these are electronically controled and the temp is set at a safe level to prevent scalding.
Generally speaking a tank or tankless set too high is dangerous and both will wear out sooner.

really comes down to what you want and can afford and what you think is best for you. In europe the tankless are more common.

Bottom line I like them and have had so far good experince with them, and haven't ran outta hot water with them. biggest downside I take longer hot showers lol... but I not complainin

No offense taken nor did I mean to say you were wrong. Just different opinions.

Plumbing heaters in series increase recovery time. The key here is to set the first heater to where it brings the incoming water to 90º and the 90º goes to the second tank which raises it to the desired temperature of 120º. So each heater is splitting the load some what. It does not increase the volume of water, if both tanks are 50 gallons you will still get the same delivery in the first hour, it just increases the recovery time.

Now if you want to increase the volume you plumb the tanks in parallel. I do not like the systems where you come in with the cold water and tee it to each heater and then have the outlets of each heater tee together to supply the house. The reason is you must have exactly the same distance to each heater and same amount of fittings to each heater to the tees. If one line is longer or there is one extra fitting in the line to one of the heaters the other heater is going to be suppling most of the hot water and will wear out first as well.

My preferred method is the first in last out parallel piping. Here is a diagram showing what I am talking about, and is the preferred method taught by A.O Smith, State, and Bradford White when I took their classes. http://www.hotwater.com/lit/piping/c...AOSCG61170.pdf

Originally Posted by chris gallo

Newer inspector here, can someone explain the purpose of this? This is the first time I have ever seen this set up.
It appears hot water is feeding into another water heater already hot? I can guess why, but is this concidered code, and can this set up damage one of the units?

chris

So to answer your question that set up is just fine. But I see a few things missing. Like unions(which might be there hard to tell) and a water shut off valve on the cold supply (which maybe out of the picture).