Cutting Edge Insights
with Dr. Lee

“Heat Rises” and other nonsense

Q:  This sounds like another Building Science Blog!

A:  That’s not a question.  But it’s correct.  Understanding Building Science is of the utmost importance when developing and investing in real estate.

Q:  Why do you say that “Heat rises” is nonsense?  I’ve heard it all my life.  What is heat, anyway?

A:  Heat is a form of energy that is present in any thermodynamic system.  Heat is transferred via one of 3 mechanisms:  Conduction, convection, or radiation.  They are discussed below.

Conduction is the transfer of heat between 2 media of different temperatures by direct contact. The pan on the stove is cold, you turn on the stove, the burner heats the pan.   You touch the pan, ouch! – the pan heats your skin.  At the molecular level, kinetic energy or motion/vibration of individual molecules is the means by which heat is actually transferred.  Some materials (metal) are better conductors of heat than others (wood). That’s why you don’t see wood frying pans.

Convection is the movement caused within a fluid or gas by the tendency of hotter and less dense material to rise, and colder, denser material to sink, which results in the transfer of heat. As you can see, “Hot air rises” is more appropriate than “Heat rises”, but it’s still not entirely accurate.

The stack effect is the phenomenon by which hot air is able to rise via convection currents within a thermal envelope of a house or a building.  Above a theoretical vertical location called the “neutral pressure plane”, heated air rises and escapes via exfiltration.  Below the neutral pressure plane, cold air sneaks in via infiltration.

Q:  But what if I have a Net Zero energy house or a passive house?  Can I build a house so tight that there wouldn’t be any neutral pressure plane and thus no stack effect of heated air rising?

A:  Yes, and that is the goal if you’re so inclined.  Building that tight isn’t cheap.  But heating air, infiltrating at 10 degrees, to a comfortable room temperature of say 70 degrees, isn’t cheap either.

In fact, I’m currently designing a home that is so tight and well-insulated, the only utility will be electric – there will be no combustion appliances or fossil fuel (natural gas). Aside from tiny utility bills, I’ll have a smaller carbon footprint and will have zero chance of inducing carbon monoxide into my living space. As well, I’ll have one fewer utility bill “customer charge” to pay every month.

I’m also considering electric-only design in a commercial multi-family development in Bay County, Michigan. I am told that there is a $8,000 – $10,000 cash credit per unit (from the utility provider) for building all electric. That can add up for 30 or more units – it may even pay for part of the development’s infrastructure.

Radiation is the transfer of energy between two objects separated in space.  From the campfire 10 feet to your chilly body.  From the sun 93 million miles to your home.  From your “radiator” – whether the radiator in question is a cast-iron monstrosity from 100 years ago, a baseboard hydronic or electric radiator, or radiant tubing beneath your floor – to your body.  Radiant heat doesn’t heat the air between you, it heats objects in its own path (you). It spreads out equally in all directions – sort of like gossip on social media.

Radiation is carried by infrared waves which are outside of the visible spectrum of light, so you don’t see it happening.

But you feel it.

Q:  What other energy concepts are poorly understood?

A:  Here’s a classic error – the notion that you don’t have to worry about heat loss as much in a basement because mother earth remains at a constant temperature of 55 degrees.

The reality is that the temperature of the earth varies considerably in the first 12 feet below the ground – the shallower depths are very close to the prevailing outdoor air temperature, then there is a gradual increase (or decrease) in temperature down to approximately 12 feet (it varies by climate zone and season).  When you consider the surface area of all your basement walls and the temperature gradient created, you can stand to lose a tremendous amount of heat to mother earth by conduction. The lesson? Insulate your basement walls very well.

Here’s another example – “I used insulation with such a high R-value that it doesn’t matter whether it completely fills my wall cavity.”  Terrible thinking.  Your attitude is that your insulation prevents you from experiencing energy losses via conduction, but a dead air space in an exterior wall sets you up for induced convection currents from temperature differences and they work against you even worse.  Some of the absolute most important things in home and building design are the wall and roof assembly details and the continuity of the control layers (water, air, vapor, and thermal) between them.

Q: What in the &^%&($&*!@#!$#!@ does all this have to do with real estate investing?!??

A: In the future,

1. Will energy (utility) costs increase or decrease? (hint: increase)
2. Will building materials increase or decrease in cost? (hint: increase)
3. Will construction labor increase or decrease in cost? (hint: increase)

If you think you can come out ahead by rehabbing a 1950s apartment building, you may be right in the short term.  But the realities of items #1, #2, and #3 above will soon catch up. If you can build or rehab efficiently with these concepts in mind, you can position yourself to be ahead of the curve.  Your end user (buyer, tenant, etc.) will pay a premium for housing that is efficient and has lower associated energy costs.  And it seems as if today’s consumer prefers things that are new more than they like an antique that has been polished.

When it comes to building with energy efficiency in mind, a friend of mine has a great saying:

You’re better off putting money here than in the bank! (with respect to dollar for dollar rate of return).

As you think about that, be thankful that we have so much more knowledge available about building science and energy efficiency and great, new materials with which to construct low- energy structures – than we ever did before. And “heat” doesn’t rise.

Until Next Time,
Dr. Lee Newton

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