I have two washing machines (one front loader & one top loader).

What consideration should be given to operate two washing machines simultaneously?

They are located right next to each other and connected to the same water valve via a dual hose adapter. The drain hose of both machines is discharge to the same sanitary pipe by way of a wye configuration.

The electrical demand is not a problem. I have concern about water flow and competing water demand, not to mention introducing water hammer problem due the to washer's closing/opening valve action. To avoid further complication, assume cold water wash only.

To borrowing some ideas, what type of plumbing configuration does a laundromat use with multiple washing machines operating simultaneously at the same time?

Thank you for your time.

Is it commercial installation or residential ? What are the chances both w/m will run at the same time ?

Water demand should not be a problem even with hot, they may take an extra minute or two to fill but what's that in the big picture. My only concern would be if they both when into a drain cycle at the same time. That drain pipe wye you mention would need to be a 4" pipe to handle 2 washers at once. How large is the pipe to which they connect?

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Originally Posted by Milo Dolezal

Is it commercial installation or residential ? What are the chances both w/m will run at the same time ?

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Residential installation. The chance of both w/m needing to run at the same time is zero but there is a want to do it for reason of time saving and convenience. The thinking is the front loader can be used to wash blanket and/or towels while the front loader can be used to wash clothing articles with gentle to medium spin speed.

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Originally Posted by ballengerb1

Water demand should not be a problem even with hot, they may take an extra minute or two to fill but what's that in the big picture. My only concern would be if they both when into a drain cycle at the same time. That drain pipe wye you mention would need to be a 4" pipe to handle 2 washers at once. How large is the pipe to which they connect?

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They connect to a 2" pvc pipe. I can move the drain hose of one w/m to allow it to discharge into the utility sink though I am not sure of the discharge rate and whether it would overfill the sink assuming the flow rate coming in to the sink is greater than the rate at which it drains (1" pipe, a guess. FYI, these w/m are in a residential setup). If such is the case, a utility sink with a large enough volume would be required to give it a certain detention time as it drains. Also the utility sink and the drain pipe wye meet at a tee connection so your point about drainage is crucial. That being said, I am still on the fence about this and hesitant about making the fathom leap.

Also, the front loader is a big water user but the top loader in general uses about 1/3 of the front loader water amount (Consumer Reports). One of my first attraction to the front loader was its lower electrical and water consumption. Because it uses less water, it does have a longer cycle time so it may even out with the top loader in term of total cost per load if electrical utility rate continues to climb.

Thanks Milo Dolezal & ballengerb1 for your help.

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To borrowing some ideas, what type of plumbing configuration does a laundromat use with multiple washing machines operating simultaneously at the same time?

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You can't compare the two. A commercial washer is 10 fixture units while a residential washer's only 3 fixture units. Regards. Tom

Hi all:

Maximum you would need would be a 3" drain pipe as that has greater area than 2-two inch drain pipes combined and would more than handle the load. But since you only have 2" present...I would go with draining one washing machine into, as you said, " a utility sink with a large enough volume to give it a certain detention time as it drains" and then drain the other washing machine using a standard 2" drain pipe with PTRAP and standpipe, but only if you want to use them simultaneously.

Glad to discuss more...

MARK

Asymptote: If it is residential installation, you should / could be fine with draining both machines into one 2" drain. Here is why:

My own sister installed 2 TROMM stackable washing machines / dryers combos after her first child was born. She had a local handyman to do the work. He split (doubled) all incoming washer connections. Both washer discharge hoses are actually only pushed into same stand pipe opening. No "Y" used here.

When I noticed the installation, I told her she should worry about possibility of drain overflow and offered to rework it for her. But she didn't want me to cut up her house now, with newborn in the house, so we agreed to wait for the first overflow and act then...

Her washers are running several times a day, everyday, all year long. And guess what? After two years of usage, and another baby, she never had single occurrence of drain overflow ! So, here you have it ....

FYI: She has brand new house, with 2" washer drain and stand pipe, set into recessed box. Water supplies are 1/2" copper. Water pressure at the washer is 75 psi.

Milo,
Do both washers discharge into the 2" stand pipe and trap at the same time?
Why does she have two washers? Inquiring minds want to know. Cheers, Tom

I have seen some new machines that can overflow a 2" drain so 2 machines into the same drain is just expecting everything to always work just perfectly.

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Originally Posted by speedball1

Milo,
Do both washers discharge into the 2" stand pipe and trap at the same time?
Why does she have two washers? Inquiring minds wanna know. Cheers, Tom

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Tom: Yes, her handyman jammed both w/m hoses into the same, 2" stand pipe / same trap. Now, I do not know how well are her w/m cycles synchronized but I did see them both run at the same time. Next time I visit her, I will test it...

It is not uncommon in my area to have 2 washers/ dryers. In case of my sis, she uses one set up just for baby related laundry while the other W/D for everything else...

Ballengerg1: I am in agreement with your statement... but, I guess, it sometimes works. I think the keyword is not to drain both washers at exactly the same time.

Thank you. You guys/gals given me much to ponder and reassurance. I was beginning to think I had to empirical time the cycle of each machine to find an ideal offset time but that is just academic speaking. Since these w/m are not identical units, demand and discharge will vary with time. One observation concerning demand is initial peak demand, especially pertaining to the top loader.

If my experience failed miserably, I shall dish out the detail for you. Otherwise, assume Murphy's law can wait Hopefully, my ideal experience would be that of Milo Dolezal's story.

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Originally Posted by speedball1

You can't compare the two. A commercial washer is 10 fixture units while a residential washer's only 3 fixture units. Regards. Tom

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Speedball1:
I have a question for you. What do you mean by 3 fixture units? I couldn't find a diagram about it on Google.

Yep, that would be key. It appears most codes are written to protect us from the worse case scenarion. Lokk at Arc faults and GFCI. We all have them now but have any of you gotten hurt before without them? They protect us but the fualts were rare. Two machine on one drain will someday, eventually both drain at the same time and I am fairly certain there will be overflow. Do any of you guys have a copy of the 2009 plumbing code, I need something looked up and I am not shelling out $100+ for the book.

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Originally Posted by ballengerb1

Do any of you guys have a copy of the 2009 plumbing code, I need something looked up and I am not shelling out $100+ for the book.

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Do you have a section number? Section title? I may be able to ask a colleague at work next week. The 2009 plumbing code you're referring to is the uniform plumbing code or international?

Bob... call your local building department... they should be able to help!

Your local library may have it too.

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Originally Posted by speedball1
You can't compare the two. A commercial washer is 10 fixture units while a residential washer's only 3 fixture units. Regards. Tom
Speedball1:
I have a question for you. What do you mean by 3 fixture units?

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In plumbing, a Fixture Unit (FU) is equal to one cubic foot of water per minute. A Fixture Unit is not a flow rate unit but a design factor. One cubic foot of water is roughly 7.48 gallons. A Fixture Unit is used in plumbing design for both water supply and waste water.
Different fixtures have different flow requirements. In order to determine the required size of pipe, an arbitrary unit is used for pipe sizing which takes into account the likelihood that all the fixtures will not be used at the same time. This is called "fixture unit" (FU). The relationship between gallons per minute (gpm) and fixture unit is not constant, but varies with the number of fixture units. For example, 1000 FU is equivalent to 220 gpm, but 2000 FU is not double that, but is only 1.5 times as much, or 330 gpm.
Laundrymat washers are in use constantly as compared to a residential washer. They use more water and discharge more into the drainage system. All plumbing fixtures have fixture units assigned to them Yours has three while a commercial washer has ten. And now you know the rest of the story. Tom

Mark I have not found any cities that have adopted the 2009 code so nobody has been able to help me yet, I will try the library like KISS suggests.