Serial vs. Parallel Water Heaters??
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Greetings,
I’m a first timer with a water heater plumbing question. Both of the gas fired, tank type water heaters in our 17 year old home failed within a few weeks of each other earlier this fall. For a variety of reasons, I only replaced one, initially, and am now going to have the second one replaced. My question relates to the way a dual tank system is plumbed. In the original setup, the tanks were piped serially, i.e. the water entered one tank where it was heated and then flowed through the second tank before circulating to the appliances where the hot water was used. To my uneducated mind, it seems like this means the first tank in the system is doing the lion’s share of the work and the second tank is mostly a holding/booster tank. Am I right about this? My P&H guy said he could plumb the two tanks in parallel if I wish. Can anyone help me understand the pros/cons of continuing with a serial setup versus switching to a parallel setup? Will one or the other approach use more energy? Any thoughts will be appreciated.
Replies
I will take a stab at this one. Unless you want to have the two water heaters supplying seperate zones for it would make more sense to have the units connected in series. A series connection allows for the maximum availabile amount of hot water. A parallel hookup could result in only one of the heaters supplying the majority of water if the preasure drops are not equal across each heater. I would not reccomend a parallel setup, could result in lukewarm water after one of the units runs out of hot water. Your observation that first unit in the series hookup will do the majority of the heating is correct. That fact that both failed in the same time frame seems to indicate that the failure mode is time rather than usage. Roger
Thanks, Roger. In fact, the second unit in the series failed first; the pilot wouldn't stay lit. But, they both started leaking at almost the same time, which, as you say, was likely mostly a function of time.
"That fact that both failed in the same time frame seems to indicate that the failure mode is time rather than usage."You're assuming that both were installed at the same time. WH 1 might have been replaced once already
BruceT
No, we're the original owners of the house & the water heaters were both original units.
I replaced a gas fired hot water heater in a school this summer, it was one of two heaters, they were hooked in series. The first heater wasn't set as hot as the last. There were no tanks in these heaters, an insulated 500 gal. tank held the water a circulating pump moved the water 24/7. Mite make a nice setup for you to lower the temp on the first tank may save energy. Unless you have 250 kids!
Thanks, McP. Thankfully, we don't have 250 kids!!! The two we had were plenty and both are now making their own way in the world. So it's just the lady's morning jet tub & my hot shower most days. Sounds like serial may the better way to go & I'll play with the temp settings from time to time.
EE's answer: Serial is slower but uses fewer wires, and the connectors are smaller/cheaper.
Series is the way to go. You get a much slower decline in water temperature during a shower that way. With two, if you keep the parts handy, you can temporarily take one out of the system when it fails, and keep going on the other until you get a replacement.
-- J.S.
Thanks Guys, I appreciate your thoughts on my question. The consensus is stay serial; I think I'll go with the consensus.
I did a serial set up for a large bed and breakfast - they never again complained of not enough hot water. You won't regret your choice.
Yeah, you definitely want serial for breakfast.
People never lie so much as before an election, during a war, or after a hunt. --Otto von Bismarck
"Yeah, you definitely want serial for breakfast."I don't know. My toaster is parallel.
That's why it takes so much power.
People never lie so much as before an election, during a war, or after a hunt. --Otto von Bismarck
OK I’m late to this thread; series vs. parallel input depends on what the output is going to be.
Here is a simple way to look at it.
Let’s say you have ten people that are going to take a shower.
Are they going to take a shower all at the same time (which would be parallel?)
Or are they going to take one right after the other (which would be in series)
It comes down to volume vs. longevity.
I mainly due parallel systems, but mine a few large water heaters serving 350 hotel rooms or 145 condos at the same time. I need to be able to provide large volumes of hot water for short periods of times verses a small flow of hot water over a long period of time.
For your basic house 2 water heaters, there is no win win situation.
Parallel systems if perfectly balanced will provide double the hot water, & have equal usage of energy, but that is really hard to achieve perfect balance.
Series systems no matter how you configure the temp’s one water heater will use more energy than the other.
If you have both at equal temps the first one will bare most of the energy usage, with the second after initial fire up will only kick on to reheat the water in its’ tank due to standing loss.
If you stagger the temps, you have to set the first tank high enough that the second tank can make up the difference during its’ regular flow.
If you have a circ system that brings up even more lop sided usage.
If the temps are staggered on a circ system the second tank will bring both tanks up to the second tank setting.
Generally when I do houses which is not that many if we have 2 water heaters they are providing hot water for separate systems.
Most of the time if a 60gallon water heater will not provide enough hot water we will turn up the temp & install a mixing valve on the outlet feeding the hot water system with 120 degree water.
Sometimes we will have a storage tank on the inlet side of a water heater that has a circ system on it.
“It so happens that everything that is stupid is not unconstitutional.” —Supreme Court Justice Antonin Scalia
We remodeled a health spa a few years ago for my family.They had a commercial water heater (150 gallons as I remember) .They were always complaining about a lack of hot water. We installed two 50 gallon heaters in series and no complaints.
I'm not saying "series" doesn't work.
Series flow is restricted to what ever the second tank outlet size is.
In most cases a small system in series is redundant, therefore it's really hard to run out of hot water in a small to moderate flow usage.
If one doesn't care about which tank is working more than the other one , then series works great.“It so happens that everything that is stupid is not unconstitutional.” —Supreme Court Justice Antonin Scalia