The house that I bought a few years ago has 2 50-gallon water heaters (I guess because of the jacuzzi). With natural gas prices headed up this winter I’d like to turn one of them off. Should I drain it first or leave it full?
Are they hooked in series? One feeds the other? That’s what I had. I left one turned off unless I wanted to use the jacuzzi. In this way, even with the water heater off, it ‘pre-heated’ the water to room temp before feeding the ‘live’ water heater.
No, they’re in parallel.
You certainly don’t want to drain it first - make sure that heat cannot be applied before you consider draining the water out.
I know that if you are leaving your house for some extended period of time that they recommend shutting off the water heater and draining it. I’m assuming this is because if you didn’t you could end up with some serious damage if the temp inside the house ever got below freezing. You obviously have no danger of freezing, but the point is that it should be safe to drain it.
Trace the output pipes first. One house that I bought had two water heaters. One handled the master bathroom only and the other handled the rest of the house. I couldn’t shut one of them off unless I was disabling hot water in part of the house.
I guess their logic was that they didn’t want the kids (or the dishwasher or whatever) using up the water so they couldn’t take showers or fill the jacuzzi tub.
They’re definitely in parallel - the output pipe from each heater enters a single pipe which the disappears into the walls.
Another question now presents. When I looked at the plumbing arrangement to be sure the heaters were hooked up in parallel, I noticed something else. Each heater has shutoff valves in the hot and cold water lines. At both ends of each valve, where it is soldered to the water pipee, there’s a lot of white crunchy material that looks like the stuff that builds up on car battery terminals. What is this? Is it harmful? Should I remove it? Do the valves need to be resoldered?
(Hmph. Hijacked my own thread.)
Don’t worry about this. It’s just mineral buildup that has collected from water which has condensed on the pipes and then evaporated. You can clean it off if you want, but it’s not hurting anything.
I’m not disputing your answer, but I’m curious as to why this deposit only occurs at the joints where the valve join the pipes.
[hijack]
I have almost the same arrangement: two 50-gallon heaters side by side. But they’re plumbed in such a way that I can make them work in series or in parellel by opening/closing the appropriate valves.
So now the questions: Assuming total consumption at one time is not large enough to drain 1, much less 2 heaters, is it more energy-efficient to run them in series or in parellel?
Assuming I turned all the tubs / faucets / showers, etc., on full blast hot, which way would provide more total hot water? How would the cooldown curves of the two methods differ? (I’m expecting the series setup would decline slowly, whereas parellel would be more of a cliff, but I’m not sure).
These are all just-for-the-fun-of-it questions, but I’ve tried to think about it and my analysis always comes down to “it depends on factors I just don’t understand well enough to work out the answer”.
Any plumbers or thermo engineers care to tackle this one??
[/hijack]
I see no benefit in draining the tank-why waste the water? Unless you’re concerned about a freeze, as was already mentioned. I’d just valve it off and cut the fuel supply.
Often people of little clue will install water heaters or other plumbing without bothering to see what kind of pipe it is being connected to.
If you have a copper connection on your water heater, and you connect it to a galvanized pipe, you need to use some kind of a buffer to prevent galvanic action from corroding the pipe. If the copper and the galvanized pipe touch, then you have made a small battery and one side of the connection will corrode, giving you all kinds of funky weirdness around your pipes (and eventually leading to failure.)
So, make sure that you don’t have copper mated to galvanized.
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Make sure you close both valves on the heater you want to shut down.
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You should either not touch that white stuff at all or cut out those sections and replace the pipe. Attempting to clean it off is a bad idea.
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If you don’t drain the heater after you shut it down whenever you do bring it back online you are going to have 50 gal of funky water to deal with. If you decide to drain it and it’s all soldered copper you are going to have problems introducing air to drain it properly. You can shut it down, hook up your hose, and pull up that little leaver on the T&P safety valve (most likely on the side of the heater) to let air in but chances are you will need to replace that valve when you decide to bring it back online otherwise it might leak. You can also try letting air in by shutting off the water to your house and leaving the valves open as well as some faucets “on hot”.
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Remember to shut off the gas valve.
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There is a yellow sticker that should give you an idea of the cost to run the unit… is it worth it to shut it down?
Hmmm. Both ways start with the same amount of hot water in tanks. Both cases have the same total water flow. Assume thermostats are set the same on all tanks. Assume that tanks fed with cold water get cold enough to kick on the burner when 50% of their volume is replaced by cold water (an arbitrary number.)
Series arrangement - Upstream tank flows into downstream. Burner in upstream tank kicks on after 1/2 a tank has flowed. Downstream tank doesn’t see temp sag until 1 1/4 tanks have flowed (since the first 1/2 tank into the downstream heater is full hot, and the second 1/2 tank is partially hot water from the upstream tank as it tries to make temp, so it will be slightly more than 1 tank before enough cool water enters to kick on thermostat.)
Parallel - temp sag and burners kick in after 1 tank flows (1/2 tank from each).
From this point on, the same amount of heat is trying to heat the same amount of water, so performance after startup should be similar.
(not sure my logic is flawless on this one.)
Presuming that the water within the tank is potable, what would make the water “funky”? Although I’m no expert on water potability, I’d consider a greater chance of cootie growth in a tank which is drained, but still is damp and now has the benefits of darkness and air for microbial growth to take hold.
Perhaps one with greater knowledge will happen into this thread and offer something for both of us. 
If you are planning to shut off one of the water heaters for an extended period (more than 6 months), drain it. If you leave water in it for awhile, you stand a risk of it developing a leak, generally at the most inopportune moment, like while you are out of town for the weekend. Of course, this can happen to anyone at any time, but why risk it for an appliance you aren’t even using? I would recommend leaving the drain open and removing the T&P valve. Leaving the drain open let’s you know if either of your shutoff valves leak by and removing the T&P vents the tank to prevent it from being damp and nasty inside.
If for a shorter period, just shut it down, but be prepared to flush it before putting it back in service. Stagnant water can get very nasty and all manner of un-nice things can grow in it. To flush it, shut off the other heater and then run the hot water in the tub for 20 minutes or so (before you turn the gas back on, of course).
Regarding the crusty white stuff at the valves, you didn’t say whether the valves were threaded or soldered. If they’re threaded, it’s probably nothing to worry about. If it’s a soldered joint, you’re looking at a probable leak in the near future and you should look into replacing the valves. If you do replace them, ball valves are definitely the way to go. They cost a little more, but they’re worth it.
In general, it’s not a bad idea to drain and flush your water heater every couple of years just to remove some of the sediment and scale that collects in the bottom. This will lengthen the water heater’s life and improve it’s efficiency. Closing and re-opening the shutoff valves about once a year and lifting the T&P is also a good idea. I’ve replaced many a water heater that couldn’t be fully shut off because of scale deposits inside the valves and I’ve seen T&P valves that were so full of rust and crap that they wouldn’t have opened until long after the tank had ruptured. If the thermostat and high limit safety fail, the T&P keeps your water heater from becoming a bomb inside your home.
Both of us? :eek:
For one thing the decaying anode rod stewing in it’s own juices is a contributing factor.
There are also things like sediment in the tank and build up on the penetrations that are just sitting stagnant in your 50 gal “tea pot”. Possible breaches in the glass lining…
I stand by my statement that if you leave it full for long enough you will have “funky” water when it comes time to bring it back online.
For my situation, VERY cold water comes in from a well. If that is allowed to sit in a ‘pre-heat’ tank to bring in up to room temp (without using any propane), I save on trying to bring it up to 110 degrees or whatever. Unless I use a real lot of water at once, this has to produce a savings.
I don’t understand. How much gas could a water heater possibly use when idle? It only has to keep a tank of water at a constant hot temperature, that could probably be accomplished with something barely bigger than a pilot light. So if you have two or one water heaters the majority of cost should come down to depreciation due to age(unavoidable) and how much water you use(unrelated to how many water heaters you have installed).