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How to Insulate a Bathtub (With Photos)

Maren is a one-person fixer of "TLC Needed" houses. She explains methods simply to homeowners who are not in the construction trades.

No wonder the bathtub water cools so quickly! This tub is uninsulated.

No wonder the bathtub water cools so quickly! This tub is uninsulated.

Problem: Bath Water Rapidly Drops In Temperature

If I weren't ripping my house and bathroom apart for other reasons, I probably would not have addressed my uninsulated bathtub. However, since I am tearing the bathroom (and adjoining rooms) down to the studs, this is a great opportunity to remedy a pet bathtub peeve of mine.

Maybe in generations before me, a bather did not stay and soak in a tub long enough to feel the water chill down, but I doubt that. Perhaps in those days when we were not as conscious about the limited resources of the earth, about saving energy and money, people could heat their bathrooms to steam room temperatures for as long as they wished. But now we are in "today," and many of us living with old tubs that allow heat to escape.

Although I am more of a shower-er than a bath-er, there are times when I want to soak. One instance in particular is after an afternoon of sled riding. I want to be able to warm myself up in a hot tub. Other times, a family member needs to be able to soak a body part (for example, sore back, derriere, leg) for medical reasons. Wouldn't it be good to have the water temperature comfortable the entire time? Thus, we come to how to insulate that tub!

Right Kind of Tub

Before you go through the trouble of collecting all the materials to do this, check to see if your tub is "accessible."

This process is for a bathtub that has no molded plastic or fiberglass outer walls on the short ends. Therefore, the space around the concave tub is easily seen and accessible after you open the wall at the end.

Some tubs are built like the soap dish pictured below. These have the concave part which is the interior of the bath tub AND also a wall which encircles that concave part. This process will not work for that kind of tub.

insulating-a-bathtub-how-to-and-photos

Step 1: Gather the Insulation Supplies

  • Whatever tools you need to open up the wall(s) touching the tub
  • Whatever supplies you need to close those walls afterwards
  • Work gloves to protect your hands
  • Face mask and googles for the same reasons
  • Utility knife
  • Optional: bubble wrap packaging
  • Fiberglass insulation rolls, unfaced or faced
  • A 3- to 4-foot-long sturdy pole, such as a broom handle or a vacuum cleaner pole
A utility knife rests on a "Pink Panther" fiberglass insualtion roll.

A utility knife rests on a "Pink Panther" fiberglass insualtion roll.

Common packaging bubble wrap

Common packaging bubble wrap

Step 2: Find the Trouble Spots

I had removed all the layers of my bathroom walls and learned that there was absolutely no insulation in either exterior or interior walls. In my house, the tub sits along an exterior wall. One end rests against an adjoining bedroom. The faucet end rests against a tiny closet in the bathroom. In addition, I have a partial view of underneath the tub from my unfinished basement. At the point where plumbing pipes go through the floor, there is a hole through which I can further ascertain the uninsulatedness of the tub. (Sigh...)

By cutting into each side wall, I was able to crack open the wall enough to see that my tub unit has vertical side walls which are absolutely empty, "unfilled" and available for insulation.

A "naked" tub end. Look at all that air space greedily clamoring to steal the heat from the tub water!

A "naked" tub end. Look at all that air space greedily clamoring to steal the heat from the tub water!

A more distant view. One can see where the interior wall insulation ends and then: nothing. No insulation.

A more distant view. One can see where the interior wall insulation ends and then: nothing. No insulation.

Step 3: Install the Insulation

(Ok. I decided that I did not want to lift the tub unit up to put insulation along the exterior wall and underneath it. Nonetheless, that is an option for the strong and hardy among you.)

I had read that even common packaging bubble wrap will perform heat insulating, so I gathered up what I had in the house. I figured that those pieces would be easier to stuff into small spaces. So, I shoved them towards the back, exterior wall which I could not reach. Then, I used a broom handle to further shove them into place.

After that, I used my tape measure to roughly estimate the length pieces of roll insulation to be placed around each tub end. Then, wearing protective gloves, I cut those lengths with my utility knife and place them inside. The broomstick was again used to help push and position insulation.

Diagram of bathtub

Diagram of bathtub

The Process Was Easy

As I positioned and pushed the insulation around the bathtub, I was pleased to find that it stayed in place. I think that this is because the space is tight to begin with, and the insulation naturally expands a little. One should not cram in so much that the insulation cannot expand. If that happens, it is less effective. Insulation is designed to have copious little air spaces.

A roll of fiberglass insulation around a tub end.

A roll of fiberglass insulation around a tub end.

Another view of roll insulation around a bathtub end.

Another view of roll insulation around a bathtub end.

What Type of Insulation Should I Use?

I used rolls because this was a DIY project. Faced insulation (it has paper on one side) is not needed, but you can see from my photos that this is what I used. The reason is that my local big box hardware stores do not carry much unfaced insulation. Another option for people who have the correct equipment is blow-in insulation. That was beyond my experience at that time.

This is the finished tub insulation. It's a great improvement over what I had before.

This is the finished tub insulation. It's a great improvement over what I had before.

Step 4: Close the Walls

For me, cardboard, plywood and white duct tape are holding the air inside the two walls I opened. That is because more work is scheduled for the bathroom closet and for the adjoining bedroom. However, if you are completely done working on the areas you needed to open, do what you wish to close the wall holes.

Enjoy a Long, Hot Soak!

Now that you've properly insulated your tub, your next bath is going to rock!

This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.

Questions & Answers

Question: Should you insulate between the wall studs behind a bathtub to solve the rapid cooling of bathwater?

Answer: Absolutely!

© 2013 Maren Elizabeth Morgan

Comments

Maren Elizabeth Morgan (author) from Pennsylvania on March 27, 2018:

CMJ, in my "before" scenario, my tub walls were hollow with one side along an outside, un-insulated wall. Therefore, heat was certainly moving into those cold air pockets along the sides in addition to escaping up. My change bought me more time with warmth in the tub. Best wishes to you.

CMG on March 27, 2018:

Just wondering, if heat rises then surely most of the heat in a bath is lost from the surface of the water, rather than downwards? Hence all the steam rising up? Would be interested to know how much difference insulating the sides and bottom of the tub makes. Is your bath now noticeably warmer? if so, then I may do the same to mine! Thanks.

Maren Elizabeth Morgan (author) from Pennsylvania on November 20, 2017:

Michael, I envision the insulated area as being quite dry with low humidity if it is sealed correctly. Therefore, there would be minimal probability of condensation.

Michael Bourke on March 31, 2017:

Would we have to worry about condensation getting the insulation wet, since there is a big temperature difference between the hot water (thus tub), and the indoor temperature?

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