Q&A - Evap Placement - Short #221

HVAC School - For Techs, By Techs

Bryan Orr

Training, Careers, Airconditioning, Self-improvement, Hvac, Business, Education, Refrigeration, Heating, Ac, Apprenticeship

4.8 • 985 Ratings

🗓️ 10 December 2024

⏱️ 7 minutes

🔗️ Recording | iTunes | RSS

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Summary

In this short podcast, Bryan talks about evaporator coil placement based on a question submitted by a listener, John. Evap coil placement differs in furnace applications versus air handlers.

When we use air conditioners with furnaces, we usually put evaporator coils on the positive side to protect the heat exchanger from rusting out during the summer (due to condensation and the chemical reactions that can occur with the metal heat exchanger). However, when it comes to air handlers, they're usually on the negative side. The coil is usually on the negative side of a fan coil or air handler because it keeps the blower motor cooler (though that doesn't make a huge difference in terms of performance).

The HVAC system will lose fewer BTUs to leakage when the coil is on the negative side, which is better for energy efficiency; those BTUs can reach the conditioned space rather than the closet, garage, or wherever it is stored. Pulling air over the evaporator coil on the negative side, however, could potentially lead to greater turbulence.

We run into challenges with evap coil placement on gas furnaces when we have dual fuel systems (a heat pump and furnace working together). You can't run gas heat over a heat pump coil due to the high head pressure, so a parallel setup would avoid the risks of high head pressure (downstream) or rusted-out heat exchangers (upstream).

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Transcript

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0:00.0	Hi-I-A. This is the HVAC school podcast. I'm Brian. This is the podcast that helps you remember some things you might have forgotten along the way, as well as sometimes has me answering questions that I may or may not be qualified to answer, but I just give it my best shot anyway. Because what the heck, right?
0:18.0	This is a short Q&A podcast. John has a question about evaporator coil placement.
0:24.9	But before we get to that, we want to thank our great sponsors. Carrier and Carrier.com.
0:29.9	Don't miss HVACR's ubiquitous event. Of course, I'm talking about AHR Expo 2025 coming to our hometown, Orlando, Florida, February 10th through 12th.
0:42.2	Explore the latest product advancements, best practices, and industry trends.
0:46.6	Register now for free at AHR.Expo.com.
0:51.4	Fieldpiece.
0:52.7	Fieldpiece.com.
0:54.6	Refrigeration technologies at refrigetec.com and specifically the new Viper wet rag heat shield.
1:01.5	The revolutionary flame resistant welding pad designed to be used either wet or dry.
1:08.3	Find a viper wet rag heat shield at a distributor near you or go to
1:11.6	TrueTechTools.com and use offer code, get schooled for a great discount at checkout.
1:18.5	Hey Brian. My question today is about evaporator coil placement. I understand on a furnace that we wanted
1:24.6	on the positive side to protect the heat exchanger from moist air being
1:28.5	drawn across it all summer long. But on an evaporator coil in an air handler, it's on the negative
1:34.1	side. My question is, do they do that because it's more efficient? Maybe it's because the air being
1:40.2	drawn across the blower motor is keeping it cooler, Or is it just because that's how they built it?
1:45.8	Hope you could touch on that.
1:46.9	Thanks.
1:47.7	All right.
1:47.9	So the question is, why do we place evaps where we do?
1:51.4	Now, actually, this is kind of an interesting thing.
	...

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