Informational Guide

How To Plumb A Bathtub

It’s not difficult to learn how to plumb a bathtub when you have the right guide. We show you how to do everything, from drains to faucets.

by Ian Haynes

Your bathroom is the most used room in your home. At the heart of your bathroom is the bathtub, which is a highly utilized fitting.  

DIY has become a lot more respected in the last few years, and more people than ever seem to appreciate just how rewarding it can be to do something yourself. On top of pride, DIY is also a fantastic way to save money.  

Plumbing can be particularly daunting for DIYers. We’ve created a separate guide to show you how to plumb your bathroombut this article will give you all the information you need to know about bathtubs, the connections, fittings, and pipes, and show you how to plumb a bathtub yourself.   

To install a bathtub, you need to understand all the different components. Here's a guide to all the different parts: 

Water Supply Pipes 

Water supply pipes, as the name suggests, supply the water to your bathtub. There are two of these, one for cold water and one for hot water, which connects to your faucet fitting. In modern bathrooms, you'll often just have one faucet, and the hot and cold water will flow into a mixer which allows you to control the overall temperature of the water centrally. 

Diverter Pipes 

Bathtubs generally have a faucet and a shower head with one water supply. A diverter pipe is used to allow water to flow up to the shower head. Diverter pipes are important because they allow you to have a single hole in your bathtub for both water suppliers. These must be fitted correctly so you have the right water pressure in your shower and low water pressure is a telltale sign that you need to replace the diverter pipe.  

Shut-Off valves 

Shut-off valves are used to control the supply of water to your home or a device. There are generally two types: fixture valves and primary valves. Primary valves are used to shut off the water supply to your whole home. These can be useful for large-scale repairs or plumbing but otherwise aren't needed.

Fixture valves allow you to shut off the water for individual pieces. This is a lot more practical and gives you much greater control. Most modern homes have fixture valves, but older homes (pre-1960) will have primary valves. Make sure your water supply is completely shut off before you start any plumbing work.  

Planar Cross 

Planar crosses are four-way cross-connection pipes. These allow you to connect up your hot, cold, drain, and diverter so that water can go everywhere it needs to. Planar cross-connections are generally only used in bathtubs, and you won't find them in the plumbing for other fittings.  

Rim 

The rim is the lip all around the top of your bathtub. This is used to help catch any liquid that might spill over the top of your tub and prevent any build-up of moisture in your bathroom. Your rim will be connected to your bathtub with sealant, and over time this can become damaged by water. Keep an eye on this and make sure you use caulk periodically to prevent any issues.  

Drain  

The drain is the circular hole at the bottom of your bathtub. This allows water to leave your tub into your plumbing and drainage system. The drain is essentially the entrance to your plumbing, and it's imperative that it's fitted properly and in the right place so water can leave your bathroom in the way it's meant to.

Drains can often become clogged with hair or other human material. Using drain unblockers and cleaning products regularly is a great way to prevent this from happening.  

Overflow Control 

The overflow is used to help catch any excess water and let it flow directly into your drain. This helps stop the bathtub from overflowing into your bathroom and prevents any strain on your drainage system. There’s usually a hole just below your faucet for the overflow pipe.  

How To Plumb A Bathtub

Considerations Before Installing or Replacing a Bathtub  

There are several factors which you need to think about before replacing your tub. These are all influenced by your home, the layout, and the way it's all configured right now. Here are the top considerations:  

Configuration 

The layout and configuration of your bathroom is a key factor when it comes to picking a bathtub. You need to understand where your drain is because certain bathtubs, like clawfoot bathtubs, need to be fitted into it directly. You also need to consider your current setup and any restrictions on your plumbing that would limit your options.  

Bathroom Size 

The size of your bathroom will directly impact the size of the bathtub you can get. Typically, bathtubs are about 60 inches, but you can find larger or smaller models if you need to. Ensure that you measure your bathroom accurately before making your choice, as even a small miscalculation can ruin the look and functionality of your bathtub.  

Traffic & Lifestyle 

The type of bathtub you choose should be influenced by the amount of use it will get. If you're in a busy home, you'll probably want a bathtub with a shower, limiting your options. You may also opt for function over form and choose more durable materials which will take greater wear and tear.

Cast iron bathtubs are probably the most durable but can be challenging to install and may not match your current design. Porcelain is normally a good option because of the classic look and durability of the material.

Maintenance Requirements 

Some bathtubs need more maintenance than others. Fiberglass and acrylic bathtubs are popular choices, but porcelain is typically the easiest to clean. Modern bathtubs are generally easier to maintain, too, so if you want an easier life, you might want to avoid older bathtubs. Remember, whichever bathtub you choose, you should try to recaulk it every 6 months. 


Bathtub Drain Rough-In   

The rough-in is where you've attached all your connections, but you haven't sealed everything up yet. This is a crucial stage in any building work because you can correct any mistakes before it's set in stone. This would also be the part of the process where you might get a professional to review everything if you're worried about anything.  

Locating the Drain Line 

To install a bathtub, you'll need to locate your drain line and cut a hole so that your plumbing can reach it. The drain hole should be at least 12 inches from the wall and typically 9-12 inches wide, so you have enough room to plumb your drain and your trap

The position of your drain will be influenced by the style of your bathtub. Clawfoot bathtubs will have exposed plumbing, so you should try to be more precise and keep the hole smaller.  

Plumbing Rough-In 

For your plumbing rough-in, you'll need to fit a 1 ½ inch pipe to the drain, which comes up about ½ inch above the floor. The majority of bathtubs will be fitted against the wall, and your water supply lines will generally come through the wall straight into your bathtub. A freestanding or clawfoot bathtub will have water supply lines coming up from the floor near the drain.  

Slope 

Your drain should slope to allow water to drain correctly. This should be set at a minimum of ¼ inch slope downwards per foot.  

Venting 

Venting is important to help prevent any dangerous gas from coming up from your sewer into your bathroom. Bathtubs utilize a wet vent which is where a vent stack is connected to your drain. These vent stacks are typically attached to more than one fitting in your bathroom.  

How To Plumb A Bathroom Drain

How To Plumb Your Bathtub (Step-By-Step Instructions)  

Plumbing a bathtub isn't overly complicated, and you can do it yourself. We've provided step by step guides for most standard setups below, which anyone should be able to follow. If you don't feel confident, then you might need to consult a professional for assistance. 

Plumbing A Bathtub Drain  

  • 1
    Install the flange  
    Spread plumbers putty around the underside of the flange and press it down. Push this into the drain hole in the bathtub and then secure it using a nut on the underside of the bathtub.  
  • 2
    Measure the holes 
    Remove the covers on the drain and the overflow drain and measure the distance. Your pipes should match these exactly.  
  • 3
    Turn the tub on its side 
    Flip the bathtub on its side so you can attach all the connections. Make sure you don’t attempt this on your own. 
  • 4
    Connect the overflow drain
    Connect the overflow drain to the bathtub using screws. This will be connected to the drain underneath the tub too. Put a rubber gasket over the drain and pipe so that it’s sealed and then screw into the overflow plate. Tighten the screws so that it’s all secure before flipping the bathtub upright again.  
  • 5
    Connect the drain to the P-trap 
    The tailpieces should be connected to a T fitting which connects both the drain outlets. It should then be connected to the curved P-trap to stop any odors traveling back up the pipe. Put a washer in place and slide the pipe into the P-trap so it overlaps by 1-2 inches; this should slide in effortlessly. Use a pipe connector to hold it in place. Tighten the compression nuts to hold the drains in place using a wrench.  
  • 6
    Test the plumbing  
    Run a small amount of water through the bathtub plumbing to check there are no leaks. Once you're content with it all, then you can seal all around the bathtub with caulk.  

Plumbing A Bathtub, Shower And A Faucet 

To plumb a bathtub, shower, and faucet, then you'll need to consider the water coming into your bathtub, not just out of it. Follow the steps above to connect the drain and the steps below to connect the plumbing bringing hot and cold water in. 

  • 1
    Install your faucet  
    Using the installation instructions, connect your faucet to your bathtub. This should screw into your bathtub directly.  
  • 2
    Connect hot and cold water  
    Connect your hot and cold water lines into your bathtub. These should run under your bathtub and run directly into a mixing valve. PEX is often the preferred piping for this because it can be color-coded. Both of these lines will connect into a mixing valve rather than the bathtub directly so that the temperature can be controlled by the faucet. The mixing valve should be connected to your faucet. Remember, this step needs to be done before you fix the bathtub in place because your hot and cold pipes will run under it.  
  • 3
    Install your shower 
    Run a pipe up the back of your bathtub for your shower. Use connections fitted into the wall to hold this in place and connect the shower head to the top of the pipe using the instructions. For brass piping, you may need to solder the top of the attachment to the pipe.  
  • 4
    Test the system
    An important step is to test the whole system to ensure that the water is flowing correctly without any leaks. It's important to do this at the rough-in stage so that you can fix any problems before everything is sealed up. Make sure that your hot and cold water supplies are both working correctly.  

Plumbing A Freestanding Bathtub 

Freestanding bathtubs give a natural feel of luxury but can seem complicated to plumb yourself. The truth is that they're actually really easy. 

  • 1
    Measure the tub 
    This is an absolutely crucial step in plumbing a freestanding bathtub. You need to determine exactly where you want it, then measure out two holes in your floor. This is where your hot, cold, and waste pipes will flow. Each of these holes needs to be roughly 2 inches in diameter.  
  • 2
    Lift the floorboards 
    Your plumbing will run under your floorboards and connect to your central plumbing. Carefully lift the floorboards so you can lay the pipe which will connect to your bathtub. 
  • 3
    Plumb the bathtub 
    Plumb the freestanding bathtub in the exact same way as you would with a standard tub (follow the steps earlier in the article) and make sure all the connections are fixed. For freestanding bathtubs, you'll want to use stainless steel covering tubes, as shown below, to connect from the floor to the bathtub because they're much more aesthetic. These are typically included in the set you buy. Make sure these are screwed in securely.  
  • 4
    Test the bathtub 
    Now test the plumbing and make sure it all works. If you're happy with it, then relay the floorboards and caulk the bathtub to keep it in place.  
How To Plumb A Freestanding Bath Tub

Plumbing A Clawfoot Bathtub 

Clawfoot bathtubs are trendy right now. They're essentially the same as freestanding bathtubs; they just have feet on the bottom to improve the look and feel.  

To plumb a clawfoot bathtub, you'll pretty much need the follow the same steps taken for a freestanding bath but with a few key differences. 

  • 1
    Measure up 
    The feet on the bathtub will impact your measurements for the plumbing, and you need to factor them in. You may need to buy a larger drain kit to accommodate the extra inches the feet add. Before starting any work, make sure it all aligns properly.  
  • 2
    Connect straight to the drain 
    Clawfoot bathtubs generally connect directly into your drain rather than having pipes running under the floorboards. You'll therefore need to fit a pipe underneath the plug straight into your drainage system, and it will need to be located close to your drainpipe.  
  • 3
    Freestanding faucet system 
    Clawfoot bathtubs use a freestanding faucet system. You’ll need to install this on the side of the bathtub by connecting the hot and cold water valves to the faucet. You can follow the steps above to do this correctly. Clawfoot bathtubs can be pretty challenging to plumb because you have a lot less flexibility and your plumbing is on show. Only try and plumb these if you’re feeling particularly confident.  

If you do not wish to do this job yourself then we recommend getting a local plumber to do the job. You can find free quotes from your area by filling in the form below.

People also Ask (FAQs)

Can you install a bathtub yourself? 

Yes, but make sure you have the right tools and equipment. You may also need a friend to help you move the old bathtub and install the new one.  

How long does a bathtub last? 

Bathtubs should typically last 10-15 years depending on the amount of use it gets.  

How much does it cost to remove a bathtub and install a shower? 

Removing a bathtub and installing a shower can cost anywhere from $1000-4000, depending on the exact specifications of your bathroom.  

How long does it take to install a new bathtub? 

It's possible to install a bathtub in a few days, but it can take longer if you're less experienced.  

How do you secure a bathtub? 

You should anchor your bathtub by drilling two holes above the studs in the lip of the bathtub and screwing it into place.  


Conclusion

Plumbing a bathtub can be a daunting task even for experienced DIYers. There are many different components involved, but if you break it down and take it step by step, it's actually not too challenging.

Hopefully, this guide has given you everything you need to plumb your bathtub yourself, and you have the confidence to try it yourself.  

Ian Haynes is an expert writer who has successfully deployed over 500 plumbing pages and other related content. He has an excellent understanding of home plumbing issues and translates his experiences via Plumbing Lab so readers can have a better understanding of common household problems. Outside of his work, Ian likes exploring Brooklyn with his Labrador.

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