ecobee’s “Frost Control” Feature (& Does It Work Properly?)

Frost control as a function isn’t unique to the ecobee smart thermostat. In fact, many old-fashioned thermostats and HVAC systems have their own versions of frost control. This setting is part of the overall attempt to wrest with relative indoor humidity.

We humans have become picky creatures when it comes to climate. While we have indoor temperature mostly under control, humidity is much more elusive. The ecobee thermostat has added in new abilities to integrate into whole-house dehumidifiers and that includes the frost control feature.

Not all good things deliver on their promise. While many people have no issue with the ecobee frost control setting, there are other users who think this feature misses the mark. There are reasons to believe they are right, as well as reasons to believe that it could just be their HVAC settings. Let’s take a closer look.

What is the Frost Control Feature?

Cleaning water condensation off a window
Cleaning water condensation off a window

Let’s start with the basics. According to the ecobee guide, the frost control setting has one job and one job only: it exists to maintain an average indoor humidity and prevents frost and condensation from developing on your windows.

This feature works by allowing you to input the energy efficiency standards of your windows into your ecobee’s settings. It then does some math based on outdoor humidity and its own humidity sensors to figure out how it can best keep your windows frost free.

Unfortunately, it seems like a lot of users struggle with this feature. It either doesn’t work and their windows frost over or it works too well, and they are up all night with scratchy throats and shuffling around for a glass of water.

So, how would this feature work in an ideal world?

What Should ecobee’s Frost Control (Ideally!) Look Like?

Under ideal circumstances, frost control makes sure that frost and condensation does not build up on your windows. Why does this matter? It’s just a little frost after all!

Well, it does and it doesn’t. If the problem was just frost on your windows, that really wouldn’t be an issue. In fact, a little frost on a window is normal. Even the most well-insulated widows are still one of the biggest sources for heat exchange and wherever heat is being exchanged, condensation can happen.

The hazard here comes from the fact that your windows aren’t just your glass windows. They are also connected into the wood and insulation of your home. Condensation can’t really hurt glass, but it can ruin wood and insulation. It can even cause dangerous mold to build up.

In an ideal world, a frost control setting uses indoor humidity reading and outdoor humidity reading to tell the dehumidifier how hard to work. It should work hard enough to prevent moisture buildup, but not so hard we humans start to feel a little dried out.

Now that we know how frost control should work, let’s figure out why it doesn’t.

Breaking Down Some Issues With Frost Control

There are plenty of issues when it comes to frost control and, lucky for ecobee users, most of these have nothing to do with your smart thermostat.

These are some of the most common reasons your frost control setting is letting you down. The key takeaway here, before we get into the details, is that sometimes a minor problem is just that: minor.

If all you’re dealing with is a little frost on very cold days, consider that normal and part of our shared human condition. It’s better to have a minor frost on the window then spend too much time wrestling with settings and residential architecture.

But, if you’ve got a major winter wonderland situation going on, you’re going to want to check out these reasons why ecobee’s frost control has been catching some flack.

Window Efficiency

Before we look at the ecobee, itself, let’s look at our homes. Windows used to just be flat glass panes. These windows had nearly zero ability to regulate temperature. This is why old homes had small windows.

If you ever take a trip to England, you can see some truly old homes with extremely small windows:

Anne Hathaways cottage with small windows
Anne Hathaways cottage with small windows

These let in some light, but more importantly kept temperatures under control. With the advent of modern HVAC, windows can be much larger as the last 100 years of HVAC technology have largely won the battle with the elements—sort of.

That efficiency number on your window is relative. Your home, your climate, and the world around you will also dictate just how efficient it can be. At the end of the day, even the most efficient window is still going to be a major site for heat exchange and that means high costs and condensation.

Upgrading your windows can help, but keep in mind that those sweeping bay windows can only get so energy efficient.

Part of the issue with frost control comes down to how humidity is measured.

Relative Indoor Humidity

When you look up the weather, you can see some pretty universal measurements. The temperature, precipitation, and other factors are easy to understand, but humidity is its own animal.

The outdoor humidity and indoor humidity are closely related, but separate. It can be balmy outside, but pretty dry indoors even without a powerful dehumidifier inside your home. This all comes down to differences in climate as well as the architecture of your home. A well-built, well insulated home can resist a good chunk of humidity on its own.

When it comes to frost control, the number we are most concerned with is the relative indoor humidity. This isn’t measured by your local weather service. This has to be measured inside your home. So how does ecobee do it?

Where The ‘Problems’ Begin: The ecobee Hygrometer

Here we get into the problem with ecobee’s frost control, at least for some users.

The way we measure relative indoor humidity with a tool known as a hygrometer. This is basically like a thermometer for humidity. You can even buy your own online. They are typically affordable as a general model works fine for most homes. We don’t need the same kind of sensitivity as a research lab would, after all.

But therein lies the problem. The hygrometer in the ecobee doesn’t appear to be very sensitive at all. A dulled edge usually isn’t the worst problem, but if we lose too much precision with our hygrometer readings, we can lose performance.

The ecobee hygrometer looks like it struggles to read humidity when things get extreme. This is a mixed bag.

What this means is that most of the time, your ecobee’s hygrometer will work just fine. As long as the humidity isn’t getting extreme or changing too quickly, it should be able to keep up with things just fine.

However, when the weather gets tough this hygrometer might give out. The downside here is that when the weather gets extreme is exactly when you are going to want to rely on your ecobee’s frost control feature.

Until ecobee opts for a more sensitive, more precise, hygrometer, there’s really only one thing we can do. If you’ve been having trouble with your frost control setting, it’s time to take matters into your own hands.

How to Get Around Frost Control

The smartest part of any smart home system is its user. If your frost control setting is letting you down, we can get it back into control by setting a manual RH for your ecobee. RH stands for relative humidity and is what we are trying to get in control of here.

The first step is to disable your frost control. This can be done in the settings menu – see 3:51 of the following video:

Once frost control is off, we can set our humidity the way we like it “manually.”

Getting in control of this setting starts with setting the humidity percent if you are using your AC to regulate your humidity. If you have a dedicated dehumidifier system in your home, this can also be controlled in the settings menu. You can also use your fan to disperse humid air throughout your home to increase the humidity, or just let the condenser take care of it if you are not.

Once you’ve got these settings where you want them, you should have worked around ecobee’s sometimes clunky frost control settings. Sometimes less is more: less smart control, and more manual control!

Does your fan persistently run with Ecobee, leaving you in search of a solution? Check out this article to understand how to turn off your fan!

About Tristan Perry

Tristan Perry is a software developer who is passionate about tech gadgets, DIY and housing. He has therefore loved seeing smart homes hit the mainstream. Tristan also has an academic background (in Math & Computer Science), and so he enjoys digging into the technical ways that smart home devices work.

Tristan owns close to a dozen Amazon Echo devices, way too many Philips Hue bulbs and lightstrips, a boat-load of Ring Cameras and Doorbells... and a bunch of other smart home devices too (from Reolink, Google Nest, GLEDOPTO and others).

If you have any questions, feedback or suggestions about this article, please leave a comment below. Please note that all comments go into a moderation queue (to prevent blog spam). Your comment will be manually reviewed and approved by Tristan in less than a week. Thanks!

6 thoughts on “ecobee’s “Frost Control” Feature (& Does It Work Properly?)”

  1. Not really correct on some details . The important issue is outdoor and indoor temperature and window efficiency (insulation quality) which determines inside glass surface temperature. If it’s too cold and humidity is too high, you get condensation and eventually frost. SO lowering indoor humidity can prevent that. Other areas of your house can also build up moisture in winter if humidity is too high and moisture barrier is poor.
    The question is whether window efficiency is high for good windows or bad ones. That would help. Personally I just turn frost control off.

  2. The frost control does work but in most areas it runs a humidifier and not a dehumidifier. It is picky to set up and most consumers do not want to pay a tech to come to adjust the settings until it is just right. Another sad point is that many techs do not know or care to learn these controls. Another weak point is that the outdoor temp is gotten from a weather reporting station based on postal code or location. In my case that can be 10 degrees different from my residence which messes with the frost control and second stage heat lockout. I have recommended that Ecobee make an optional outdoor sensor that would fix this problem.

  3. The difference in heat and moisture are culprits. Long a go (2011), we had code to control Nests from a separate website that would read the local outdoor temp and humidity, compare to the indoor temp and humidity and adjust the indoor humidity to a suitable level. It worked great, making adjustments by taking readings once every half hour. One could tweak the code just a bit to adjust for your home preferences. Alas, when Google bought Nest and started playing with it, its functionality stopped. As a “smart thermostat” I never understood why Nest never incorporated the function. Even if rudimentary, it was way better than manual… and really, your window condensation is only a rough indicator. I was hoping that Ecobee had actually done it. To be functional, it doesn’t need to be that complicated. R-value of your windows may not be an indicator of what’s happening in you walls.


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