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 Bathtub to shower - drain size
Author: HelpMePlumb (FL)

We want to remove a LH drain bathtub and replace it with a 60 x 30 shower pan with a LH drain. It's doubtful the existing drain stack (2nd floor unit) is any larger than 1 1/2". Do we need to use a 2" trap even tho it would connect shortly to the 1 1/2 drain pipe? The plumber thinks its a non-issue but what about the lack of an overflow on the shower pan? Would the 2" trap help with that issue at all?

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 Re: Bathtub to shower - drain size
Author: RWP (SD)

There is a reason the majority, if not all, plumbing codes call for a 2" drain on showers and that is to safely and completely carry off the waste water. A 2" trap will help a little but a total 2" drain meets the plumbing codes.

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Retired after 50 years of plumbing and heating.

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 Re: Bathtub to shower - drain size
Author: Timsplumbing (MA)

Is there a toilet in this bathroom? If so you will have a minimum of a 3" stack.

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 Re: Bathtub to shower - drain size
Author: NickM

I had the exact renovation done recently in my bathroom. Plumber replaced the toilet drain and incorporated the 2" shower drain into this. Unfortunately he had the subfloor installed before I had a chance to see exactly what was done.

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 Re: Bathtub to shower - drain size
Author: jerco (MD)

If you're tying into 1 1/2" copper or plastic you should be okay. If it's 1 1/2" galv. steel or cast iron then no way.

If I had to do it, I would reduce right below the drain fitting (above the trap) so when the drain starts to slow down you can remove the strainer and manually clear the way.

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 Re: Bathtub to shower - drain size
Author: Timsplumbing (MA)

If the plumber is pulling a permit it is an issue.

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 Re: Bathtub to shower - drain size
Author: packy (MA)

i'm with jerco on this..

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 Re: Bathtub to shower - drain size
Author: mr leak (CA)

A shower is to be a 2 inch drain.A 3 inch toilet drain needs a 2 inch vent and can be vented with the shower but has to be 2 inch

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 Re: Bathtub to shower - drain size
Author: PBwrencher (WI)

2" is minimum in every plumbing code throughout our country,:)

It will work with a 1 1/2" drain about as well as a car that needs a good tune-up will work, it's never going to work correctly until it's done right and will give you problems down the road when you least need them.:think2:

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A bath a day will keep you healthy in every way.

Safe plumbing brings life and health giving water into our homes, businesses, hospitals and takes away death and disease causing waste.

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 Re: Bathtub to shower - drain size
Author: waukeshaplumbing (WI)

if you want it rigged then keep it 1 1/2"...if you want it correct then change it to 2"

you need to trace that 1 1/2" line all the way back to the 3" drain, cut out the 3x1 1/2" Y and install a 3x2 Y and rerun the 2" drain....it typically means repiping most of the drains for the bathroom...it can be a full day or 1/2 day project since its on the 2nd floor...it can be done...

i recommend you fire any plumber who says 1 1/2" is ok....he rigging it and is not a good guy...bite the bullet and hire a quality plumber AND GET PERMITS....no way a 1 1/2" drain will fly with an inspection.

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 Re: Bathtub to shower - drain size
Author: hj (AZ)

You are assuming you have a problem before you know if you really do. Many plumbers, myself included, use a 2" pipe to the tub and reduce where the tub connects to the trap. Until you remove the tub, you do NOT know what size they used.

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 Re: Bathtub to shower - drain size
Author: SwimRunPlumb (MI)

1 1/2 drain is now code for residential showers in Michigan. You will also be fine (I am not saying it will be to code in YOUR area though, just that it will work).

Tubs drain with 1 1/2, a shower is no different. It is just more a a safety code so that the shower has less of a chance of overflowing over the 5-6 inch curb if the drain backs up.

With low flow shower heads nowadays instead of the 5-6 gallons per minute that the old shower heads used to dump out, 1 1/2 is perfectly suitable.

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 Re: Bathtub to shower - drain size
Author: waukeshaplumbing (WI)

unless its more than 6' i dont ever see anyone run a 2" drain for a tub...HJ does, but he may be the only one...pretty much zero chance its 2" already

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 Re: Bathtub to shower - drain size
Author: hj (AZ)

quote; 1 1/2 drain is now code for residential showers in Michigan

And a "code" is a "minimum standard", and if it is the IPC code, it is governed by contractors who wish to install to the cheapest level.

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 Re: Bathtub to shower - drain size
Author: LemonPlumber (FL)

where you seem to be reading the code use very well .you may need to leave the plumbing changes to your plumber.I agree a 1 1/2"drain may foul faster.will it work ?can it with out any doubt.If you must have it to code the value of change may not allow it to be done.Why the end change and the fixture selection? this where your plumber may be able to give you code approved alternatives.We can re-plumb from floors below to floors above and correct most installs.but?again have a little faith. If your plumber will agree to install a two inch fixture to any 1 1/2"branch arm is An alternate where inspection and past code is allowed.

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 Re: Bathtub to shower - drain size
Author: PBwrencher (WI)

Tubs and showers are different.:) The bathtub has an overflow that aids when discharging water and showers don't.:think2:

Try this sometime, wet down a dishtowel and plug it off in such a manner that is completely air tight and watch how slow the water drains out of a 1/2 full tub. Now remove the dishtowel fill tub again 1/2 full and you will see the difference.:think)

I would like to know what section of the Michigan Plumbing Code you are referencing. When I talk to my brother in Grand Rapids, I will have to bring that to his attention.(?)

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A bath a day will keep you healthy in every way.

Safe plumbing brings life and health giving water into our homes, businesses, hospitals and takes away death and disease causing waste.

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 Re: Bathtub to shower - drain size
Author: hj (AZ)

quote; The bathtub has an overflow that aids when discharging water and showers don't.

The overflow has very little, if any, effect on the rate of draining. The tub has a 1 1/2" drain because that is the size of the strainer in the bottom of the tub, and even that is severely restricted by the actual opening in the tub drain, either by the slots in its cover, or the limited space when the plug is lifted.

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 Re: Bathtub to shower - drain size
Author: SwimRunPlumb (MI)

I did not think that the overflow had anything to do with the draining of the tub, and I WAS thinking. I think that is a popular misconception.

I was wrong, it is not just the residential code, it is also the commercial code and is governed by the flow rate of the showerhead.

Table 709.1 of the Michigan Plumbing Code.

Showers (based on total flow through showerheads and body sprays)

5.7 gpm or less 2 dfu's and 1 1/2" minimum trap
5.8 to 12.3 gpm 3 dfu's and 2" minimum trap
12.4 to 25.8 5 dfu's and 3" minimum trap
24.9 and above 6 dfu's and 4" minimum trap

You should not have to bring this to your brothers attention if he is licensed and following the law. All licensed journeyman and masters are required to take a code update course every 2 years. He should be well aware of this. Who does he work for? I am also in Grand Rapids. Jenison actually, just outside GR.



Edited 1 times.

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 Re: Bathtub to shower - drain size
Author: LemonPlumber (FL)

pb change the riser distance from the trap on a tub or shower with or with out over flow and the flow rate works to the fall not the relief of vacuum of an over flow.where the first turn of the flow is 90 on a tub. To change the waste to a shower may not need to be 90.If your plumber lets you use this new install and has no problem passing inspection .let him work.

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 Re: Bathtub to shower - drain size
Author: PBwrencher (WI)

Don't believe me, don't let me convince you.:)

Try it both ways as I stated above without the plug, (of coarse use your plunger cup over the opening prior to testing) a couple of times even with a stop watch and note the difference.:)

- - - - - - -

A bath a day will keep you healthy in every way.

Safe plumbing brings life and health giving water into our homes, businesses, hospitals and takes away death and disease causing waste.

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 Re: Bathtub to shower - drain size
Author: PBwrencher (WI)

Thanks for the code update, my book is from awhile back, it does make more sense than the old code.

But then again; what if they change there shower head from a measly 2.75gpm to a nice 7.5gpm for a better shower as so many people do after inspection? Do they have to change there drain piping:?:

My brother worked with my dad a Master Plumber in Traverse City for years and then got his architects license and is now off on bigger and better things.

- - - - - - -

A bath a day will keep you healthy in every way.

Safe plumbing brings life and health giving water into our homes, businesses, hospitals and takes away death and disease causing waste.

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 Re: Bathtub to shower - drain size
Author: SwimRunPlumb (MI)

Just because 1 1/2" is allowed, that doesn't mean many, if any, plumbers are doing it. I will always run a shower in 2", probably out of habit I guess. I was merely saying it is allowed under our code, and will work.

I have never upsized a showerhead after inspection? I guess if they have an 1 1/2" drain and then upsize the showerhead after inspection and it can't keep up, it is their own fault (homeowners and plumbers).

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 Re: Bathtub to shower - drain size
Author: hj (AZ)

quote; then got his architects license and is now off on bigger and better things.

Noe, HE can design buildings which are difficult, or almost impossible, to install the plumbing in them.

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 Re: Bathtub to shower - drain size
Author: dlh (TX)

codes want 2" on shower only drains for one reason and that is because a tub will take a long time to overflow if the small 1 1/2" drain backs up and a shower you normally only have a 4" threshold and it does not take long to overflow it if there is a restriction so they require 2" pipe to reduce the risk of a complete clog not to mention the larger area to carry the water away faster.

1 1/2" will work but most codes also do not allow you to reduce pipe size in a drain so if you stayed with 1 1/2" reduce the 2" shower drain at the drain so you don't have a restriction built into the drain pipe

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PLUMBERS "Protecting The Health Of The Nation"

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 Re: Bathtub to shower - drain size
Author: PBwrencher (WI)

Luckily he does know the ropes in that department and he has the knowledge most artitechs don't which is working with your head and physically working with ones hands to make a building actually come together.:):think2:

- - - - - - -

A bath a day will keep you healthy in every way.

Safe plumbing brings life and health giving water into our homes, businesses, hospitals and takes away death and disease causing waste.

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 Re: Bathtub to shower - drain size
Author: ArnieR (IL)

The IPC is right on this issue. You do not need, nor do you want a drain larger that 1.5" The UPC is completely ignoring the science on this issue. The 2" drain was necessary when showers flowed at more than 8gpm. Unless you install 7 showerheads in the shower compartment, you do not want a 2" drain. If you want to maintain the proper velocity of water flowing through the drain, you need the 1.5" or less. Slow moving wastewater causes solids to settle and accumulate in the drainline. The UPC might require the 2" drainline, but that is because the UPC ignores the laws of science and logic.

You may have to choose between following the code, or installing the correct drain size.

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 Re: Bathtub to shower - drain size
Author: dlh (TX)

i havent gotten a copy of the 2009 code yet so i dont know if they changed it but the 2006 ipc requires 2" pipe for a shower

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PLUMBERS "Protecting The Health Of The Nation"

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 Re: Bathtub to shower - drain size
Author: hj (AZ)

Unless I have missed something, you will also NOT find any 1 1/2" shower drains.

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 Re: Bathtub to shower - drain size
Author: PBwrencher (WI)

I got a 3" drain for my on slab shower at my lake cottage and it has been working great for years.:)

- - - - - - -

A bath a day will keep you healthy in every way.

Safe plumbing brings life and health giving water into our homes, businesses, hospitals and takes away death and disease causing waste.

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 Re: Bathtub to shower - drain size
Author: LemonPlumber (FL)

PB?You can get 7.5 from the valve tubing?

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