Checking Evaporators on Furnaces
In Florida, there are not many gas furnaces—at least not as many as up north. Sometimes, we can look like real dummies compared to techs who work on them every day. One thing to know about 80% gas furnaces with cased evaporator coils is that you can often check the evaporator coil by removing the […]
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Furnace Air Temperature Rise
Every gas furnace data plate/tag has a specification for the temperature rise through that furnace. It is shown in a range, like 50-80° or 45-75°. Those two numbers are the lowest recommended temperature rise, and the highest allowed temperature rise through the furnace is usually a 30° difference. When possible, we want to get the rise […]
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Clocking a Gas Meter (It’s not that hard)
I've heard a lot made of clocking gas meters over the years, and honestly, in Florida, there isn't too much call for heat. There are even fewer furnaces. I was pleasantly surprised when I found out how easy it actually is. Here is how you do it, step by step: #1 – Make sure all […]
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Tech Question – Why Do ECM Motors Trip a GFCI?
This question was submitted on the site in response to the recent GFCI tip. It's a good question with several possible answers. What do you think? Hey Bryan, I have had a few instances where we are firing off a furnace in a new build with a temporary power pole outside with gfci outlets installed […]
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Combustion Air
To maintain combustion (burning), you need three things: fuel, heat, and oxygen. If you have all three in the proper proportion, you can maintain a continuous state of combustion. Remove one (or reduce one sufficiently), and the triangle of combustion can collapse. In a common NG gas furnace, the heat is the igniter, the fuel […]
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The Good Old Heat Anticipator
As a technician, you most likely know some customers who still have an oldie thermostat (you know, those old mercury bulb things, like the round Honeywell CT87 and such). Keep in mind that those usually have an adjustable heat anticipator. If you’re newer in the field, you may not have seen or worked with those […]
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Condensate Drainage in a High Efficiency Gas Furnace
This article was written by HVAC/furnace technician Benoît Mongeau. Thank you, Ben.     High efficiency (or 90%, or condensing) furnaces use a set of two heat exchangers to retrieve more heat from the combustion products than their mid-efficiency counterparts. Because of this, they generate flue gases much colder than those of a mid-efficiency or […]
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Properly Diagnosing a Gas Furnace Pressure Switch
This article was written by boiler technician Justin Skinner. Big thanks to Justin for being one of the rare techs who cares enough to take the time to write something like this. Thank you, Justin! Pressure switches are used in a variety of applications. Generally, they are a normally open switch that closes with either […]
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Does a Furnace Decrease Humidity?
Does heating the air cause the humidity in the air to decrease? Yes and no. Heating air causes the RELATIVE humidity percentage to decrease, but it does not change the overall moisture content in grains of moisture per lb of air. Many old-timers will swear a blue blaze that oversizing a furnace will directly result […]
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