Think of Your House As a Bathtub…Full of Heat

by Erik North on October 17, 2012

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One of my posts on dual flush toilets was recently published on Green Building Advisor. The post was on heat absorbed by cold water in the toilet tank. The broader point was how complex and interconnected a house’s thermodynamics are.

But for anyone who does not have some high end energy modeling software installed in their head, this is hard to envision. To make it simpler, think of your house like a bathtub.

Once Again – Your House and Heat

I’ve written a few times about heat energy and heat movement. Heat moves by convection, radiation and conduction. There are thousands of interacting factors and we’re ignoring all of them for a single picture: The heat in any building enclosure will always equal the heat added minus the heat lost. Any tweaks of heating systems, insulation, sunlight or temperature changes only ever alter that simple picture.

This is a nice conceptualization and we can tie it to a simple image. Some folks use buckets of water or grains of sand. During audits, I tells folks to imagine a bathtub filled with warm water.

Your House as a Bathtub
The water is the heat in your house. In this house as a bathtub metaphor, the escaping heat is swirling down the drain. How will you best keep the water in the bathtub? How will you best keep the heat in your house?

This seems easy and real obvious. If you were taking a bath and the hot water were gushing away, you would plug the drain.

But how many times has someone thought about adding a pellet stove or wood insert or an electric quartz heater to maintain heat in a house. That’s the equivalent of running a hose into the bathtub so that the water keeps up with the drain. Idiocy.

Folks try a variety of solutions: Crank the heating system, add a pellet stove, add a monitor heater. However, they are all versions of the same thing.

The smart answer is insulation and air sealing. Reduce heat loss to plug the heat draining out of your bathtub house.

{ 1 comment… read it below or add one }

Allison A. Bailes III, PhD October 17, 2012 at 8:13 am

Good article, Erik! I love the image of running a hose to the tub to provide more hot water instead of plugging the hole.
I wrote a similar article at the beginning of this year, titled, Your HVAC System Is the Faucet; The Building Envelope Is the Cup (


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