Author Topic: Can you have too much air return?  (Read 290 times)

Offline prdufresne

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Can you have too much air return?
« on: November 16, 2018, 03:49:57 PM »

My wife and I recently purchased a log home. I mention it's a log house because running additional ducts is no simple task. The first thing we did was replace the electric forced-air furnace with an cold climate air-sourced heat pump with a propane furnace as backup. We also have a wood burning fireplace on the main floor. It may also be worth noting that the staircase to the basement is an open staircase. There is no door to close off the basement.

When the furnace is running, the basement stays warm, keeping basically the same temperature as the rest of the house. When we use the fireplace, however, the basement gets cold, and before you ask, we always leave the furnace fan running.

I was tracing the duct work through the house and discovered that the air return (5x10) at the top of the stairs (at the highest point in the house) is not connected to the furnace at all but to an air exchanger. The output of the air exchanger is in one of the basement bedrooms, but even with the air exchanger running, the being dumped in the basement is cool, presumably because the air exchanger loses some of the heat to the outside when it's running.

The air returns on the main floor are in the floor on either side of the staircase and are 6x24 and 8x24inches. There are also two cold air returns in the basement, in the wall, at floor level. The two in the basement don't feel like they're drawing any air, however.

My initial thought was take the return duct at the top of the house and connect it to the furnace air return so that it would mix the warm air from the top of the house with the cool air in the basement and circulate it throughout the house.


My concern is that since the basement returns don't feel like they're drawing any air, if I add the return from the top of the house to the system, it won't draw air either because the path of least resistance is to draw from the two large grates on the main floor.

I would appreciate any suggestions on how to improve the air flow so that heat from the fireplace gets circulated better throughout the house. In the summer we use the ceiling fan to draw heat down from the high ceiling, but that doesn't seem to help the temperature in the basement.

Thank you!

Offline Admin

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Re: Can you have too much air return?
« Reply #1 on: November 16, 2018, 04:03:27 PM »
It definitely sounds like you have a problem with the basement return air.  I would try to see if something is not connected properly.  It sounds like the fireplace is fooling the thermostat and preventing the furnace from starting which is causing the basement to get cold.

You could look at the Ecobee thermostat with room sensor.  The sensor would stay in the basement and can help average things out, however if the furnace ran to heat up the basement, while the fireplace was running, you could end up with an even hotter main floor.  The basement return air is crucial so I would have someone look at this to see why it isn't pulling the cold air out the basement.

It sounds like the HRV is installed as a partially dedicated system.  Normally a simplified system would only connect to the return air duct in the basement, and use the furnaces ductwork to exchange air throughout the house.  With a partially dedicated system normally the HRV would only have vents sucking air from bathroom or the kitchen.

Was there a make up air unit installed for the wood fireplace?

Offline NoDIY

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Re: Can you have too much air return?
« Reply #2 on: November 16, 2018, 05:11:14 PM »
Just for clarification

When u heat using the central system you are getting proper heat distribution? And only have issues when u run the fireplace?

What type of fireplace is it? Some wood fireplaces suck alot of air out of the house.. While on the main floor u may feel warmth as will your thermostat.. The basement could get cooler..

Admin ecobee suggestion with basement sensor soundsike a good idea. It will force the furnace on help keep the basement warm.

Offline prdufresne

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Re: Can you have too much air return?
« Reply #3 on: November 16, 2018, 07:52:54 PM »
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Was there a make up air unit installed for the wood fireplace?

There wasn't, but I assumed the air exchanger was serving that function.

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When u heat using the central system you are getting proper heat distribution? And only have issues when u run the fireplace?

That's correct. Only when the fireplace is running.

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What type of fireplace is it?

The fireplace is a sealed unit with an external air intake. It doesn't draw air from the house.

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While on the main floor u may feel warmth as will your thermostat.. The basement could get cooler..

I figured that was the case, but was expecting the heat to be collected by the air returns and circulated to the basement. This is why I was thinking of taking the exchanger intake at the top of the house and re-routing it to be an intake for the forced-air system. My fear is that it won't draw much air from it since I have so many large returns already.