Is it worth insulating a bathtub?

[revelation]

We have a lot of expanding spray foam left over from our project.  We at installing a steel Bette bathtub, and in thinking of ways to use up our foam I thought it may be worth spraying the entire underside of the tub to help keep the water warmer for longer.

 

Any thoughts on this? Would it be worthwhile? Or make such little difference that it is not worthwhile?

 

Thanks in advance. 

[Kelvin]

Yes it will help. Pre-heating the tub with much hotter water than you’d bathe in also helps. Also use bubble bath as the bubbles slow down the evaporative cooling process. 

Edited December 29, 2022 by Kelvin

[revelation]

Is this something you have done?   How much would it help by do you think?

[Miek]

The vast majority of heat loss is from the surface of the water via evaporation.  Bubble bath makes the biggest difference to keeping the water warm IMO. 

[SteamyTea]

What is the aim here?

 

[joe90]

22 minutes ago, SteamyTea said:

What is the aim here?

 

 

7 hours ago, revelation said:

to help keep the water warmer for longer.

 

[Kelvin]

7 hours ago, revelation said:

Is this something you have done?   How much would it help by do you think?

Nope and no idea. You could experiment with a metal cooking dish. Fill with hot water and measure the temp every five minutes over an hour. Then do the same after adding a layer of foam to the bottom of it. 

[Roundtuit]

I stuffed a load of PIR off-cuts in the void under and around the bath before I boxed it in.  No idea if it has any benefit though, other than saving a trip to the tip...

[Conor]

I'd sell the foam cans and go out for a nice meal instead.

[twice round the block]

If you get any form of leak, in the sealant or pipework, blockage in the trap your in for a whole load of grief if the area is pumped full of that stuff.

[Ferdinand]

How will you get at the pipes?

[Tennentslager]

I misread the bit about bubble bath as bubble wrap...stuff if full with bubble wrap instead...?

@Conor speaks sense, stick them on gumtree or eBay and have a curry

[SteamyTea]

6 minutes ago, Tennentslager said:

have a curry

And make your own bubble bath

[Nickfromwales]

Spraying 30mm of foam will

defo help keep the bath warmer for a bit longer, and leave access for plumbing ( with some strategic foaming / cutting out ). 
Certainly won’t hurt that’s for sure!! 

[Nickfromwales]

1 minute ago, SteamyTea said:

And make your own bubble bath

Normally ass-ociated with a pasty-rich diet. 💨 🤢

[Pocster]

I’ve found at least 3 people in the tub keeps the water warm .

[Onoff]

7 minutes ago, pocster said:

I’ve found at least 3 people in the tub keeps the water warm .

 

& icky...

[Onoff]

Mine is a semi sunken bath, floor of bath level with bathroom floor, set in a marine ply surround.

 

 

 

I insulated the two "outer" walls. 

 

 

[Adrian Walker]

Top tip.  When you have finished using the bath, don't empty it until the water until it has cooled to room temperature.  

[Pocster]

1 hour ago, Onoff said:

Mine is a semi sunken bath, floor of bath level with bathroom floor, set in a marine ply surround.

 

 

 

I insulated the two "outer" walls. 

 

 

Best way to keep your bath warm is finish the (expletive deleted)ing ufh 😎

[TerryE]

1 hour ago, Adrian Walker said:

Top tip.  When you have finished using the bath, don't empty it until the water until it has cooled to room temperature.  

Great minds ... Jan thinks I am mad, but tolerates this one.

 

We use maybe 100ltr in a typical bath and maybe 120 lr in a full one, but let's stick with the 100 figure.  We have our baths reasonable hot, let's say 45°C; our rising main is currently at 7°C and bathroom ambient at 21°C so the Δt riser -> bath is 38°C and ambient -> bath 14 °C. By letting the bath cool to ambient we lose roughly 37% heat to the drain and 63% to space heating.  The specific heat of water is ~ 4.2 kJ/kg/K so cranking the numbers, we have 4.2×100×24/3600 kWh = 2.8 kWh going into space heating and 1.6 kWh going down the plug hole.

 

In our case we have a low energy house with electric resistive heating and 2.8 kWh is a non-trivial % of the daily heating requirement so this is definitely worth doing.  Incidentally:

• We have SunAmps heated overnight for storage so this bath costs about 80p on our tariff of which 50p is offset against space heating, so the effective cost is 30p (plus the 0.1m³ water).
• We have a double bath and use this feature (though usually serially these days 😉) so the cost per person is 15p.
• We have softened water, so bathing generates very little scum and the bath is easy to wipe clean, even if the water is at room temp.

Edited December 29, 2022 by TerryE

[Onoff]

1 hour ago, pocster said:

Best way to keep your bath warm is finish the (expletive deleted)ing ufh 😎

 

So when you've finished with the basement captives is it straight into a bath of hydrofluoric acid? 

[Marvin]

I would not use foam. I have used mineral wool. Without fluffy, when the bath is full of hot water, the air underneath warms up, so I believe it keeps the bath warmer longer. That and making sure the space under the bath is airtight.  

 

M

 

 

 

[JohnMo]

Our bath has been used once in the last year, I wouldn't bother. Plenty of other stuff to get on with.

[revelation]

9 hours ago, Ferdinand said:

How will you get at the pipes?

 

I was planing to turn the bath upside down and foam it before it is installed, so I wont be covering all the pipes etc.