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Old 03-16-2014, 03:09 PM   #1
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Number of air returns in home


Hello. Quick background on my home. Built in the late 1990s and was modified to some extent by someone growing marijuana in the basement. After their death in the 2000s I purchased the home and recently learned of the homes previous use from the neighbors. I had a new HVAC installed this year and the company was less than helpful. After shelling out $6800 on a 4 ton 14seer traine unit, I cannot afford a new company to come in and give advice.

The home is built into a hillside and includes a lower finished walk out basement, a crawl space, and a single upper floor.

The upper floor is 1724 sq. ft.
The finished walk out basement is 598 sq. ft.
Crawl space is approx 1056 sq ft.

I've never owned a home with a basement, but it has always struck me as odd that I have two air returns in the 598sq. ft. basement and two air returns in the upper floor 1724sq. ft. area.

The returns in the walk out basement area are a 25x14 for a 364sq ft area and a 14x14 for a 234sq ft area. On the living floor in family room up high on ceiling is a 24x24 air return for the whole west side of my home. On the east side there is a 12x12 located in the hallway of my master bedroom.

I only use the walkout basement for storage and frankly don't care about its temperature. I had already closed the single air supply vent that was down there. I've wanted to also block of one or both of the returns down there. In the winter, the air is very cool in the walkout basement and the system sucks that cool air and sends it to the living area which in my mind causes the home to cool slower.

When this has been explained to the installer he tells me that the 4 ton system was installed based on the needs for heating and cooling that 598 sq ft basement area as well as the living area and blocking those basement returns would cause problems with the load of the system.

I personally feel the returns in the basement were added by the marijuana grower as the county tax records used to list the area as an unfinished basement which I would assume wouldn't have any heating or cooling. I also assume a indoor marijuana grow would generate a lot of heat so you would want to have a lot of that hot air sucked out.

Can anyone help me out with this? Are my ideas way out in left field??

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Old 03-16-2014, 03:46 PM   #2
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The basement would have been conditioned when the original system was installed, whether it was unfinished or finished. It helps to keep the upper level warmer in the Winter and cooler in the Summer.

What is the size of the return vents on the main living level and down in the basement?

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Old 03-16-2014, 03:51 PM   #3
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The returns in the walk out basement area are a 25x14 for a 364sq ft area and a 14x14 for a 234sq ft area. On the living floor in family room up high on ceiling is a 24x24 air return for the whole west side of my home. On the east side there is a 12x12 located in the hallway of my master bedroom.
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Old 03-16-2014, 04:44 PM   #4
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You are fine with those. That 12x12 is a little on the small size. But the 24x24 makes up.

I would not worry about it, as long as there is some way to place conditioned air into the basement, not just pull it out through the returns.

Forget about the what the pot grower did. That is in the past. If they had done any changes, they would have disconnected the vent from the furnace or cut into it, or used a fireplace if there was one, to get the smell of the pot out of the house.

They also would have changed the panel, or possibly cut into the feed coming into the meter, before it got to the meter, if it was a large operation.
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Old 03-17-2014, 06:31 PM   #5
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Thanks for the responses. I will just stop worrying about it. Must still not make sense because I don't have HVAC training.

It was a major operation and the HVAC system had been modified to cool the grow. Two large ducts had been diverted to the grow room area (with the 25x14 return). Before we purchased the home this duct was removed and a cap has been placed over the opening. A single 6" duct supplies the entire 598sqft basement(with 2 returns [14x14 & 25x14]). In my mind this cant be right. Again, this must be do to my lack of HVAC training.

I installed a nest a few days ago and the system seems to be running much better so my concern regarding the install and previous uses of the home have calmed. The crappy thermostat caused the system to run so poorly I had convinced myself the modifications from the marijuana grower were the cause.
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Old 03-17-2014, 07:23 PM   #6
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Number of air returns in home


They way you learn is by asking questions, and reading about it. The cap may have been done due to there was not enough return from upstairs.

As for the Nest, watch on how it behaves. Every now and then they mess up the software. As long as you had the C wire connected to the Nest, you should have no charging issues. Some people have had issues with the thermostat battery not charging, due to how the system motherboard or transformer will not send power to the thermostat, while the unit is not running.

The only thing I have from Nest, is the Nest Protect CO/Smoke units. They interlink with the Nest thermostat, so that if there is a CO or Smoke alert, it shuts down the furnace.

I did not notice if you had stated that there was vents to allow heated or air conditioned air into the basement.

For my Thermostat, I look at the future weather for the next ten days and adjust the program on it, so that it is not always at 68 when it may be warm out. A/C, I also do the same, but have to start running usually in April during the day, due to my wife's allergies and my Sinusitis. I keep our A/C around 69 at night, 71 to 72 during the day, depending on how hot it is outside. Most of the time, 71 does just fine and the furnace cycles better at that.

Also if you have not checked the attic for proper venting, make sure the soffit is properly vented, not clogged with insulation, and that you have a way for the hot air to escape out of the attic. Some like myself have to use a thermostat controlled power vent for the attic, due to the design of the attic area.

I like to keep my attic around 95º f at all times in the Summer. It helps with the a/c cooling.
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Old 03-17-2014, 08:09 PM   #7
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Number of air returns in home


Generally speaking, your return air should be equal to, or slightly greater than, the heat supply ducts. It sounds like you only have one 6" heat run in the basement, yet you have a huge amount of return air. I would imagine that the return in the living room ceiling isn't working very well, as well as the other return in the first floor, as the system is getting all the air from the basement. Path of least resistance. It sounds like your entire heating system is unbalanced because of this.

There are quite a few knowledgeable and helpful gents here that work in the HVAC field. I'm sure they'll be along shortly to give you more helpful information......
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Old 03-17-2014, 08:52 PM   #8
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As for the Nest, watch on how it behaves. Every now and then they mess up the software. As long as you had the C wire connected to the Nest, you should have no charging issues. Some people have had issues with the thermostat battery not charging, due to how the system motherboard or transformer will not send power to the thermostat, while the unit is not running.

I did not notice if you had stated that there was vents to allow heated or air conditioned air into the basement.

Also if you have not checked the attic for proper venting, make sure the soffit is properly vented, not clogged with insulation, and that you have a way for the hot air to escape out of the attic. Some like myself have to use a thermostat controlled power vent for the attic, due to the design of the attic area.
Yes my system was wired with a C so my nest works great so far. My attic includes ridge vents and soffit vents as well as those dome fans on the top so I think it is well ventilated. And yes, there is one supply measuring 6" to the walkout basement area.

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Originally Posted by jomama45 View Post
Generally speaking, your return air should be equal to, or slightly greater than, the heat supply ducts. It sounds like you only have one 6" heat run in the basement, yet you have a huge amount of return air. I would imagine that the return in the living room ceiling isn't working very well, as well as the other return in the first floor, as the system is getting all the air from the basement. Path of least resistance. It sounds like your entire heating system is unbalanced because of this.
This is exactly my thinking. I asked the installers and they were less then helpful. I am more than capable of taping into the duct work or removing a return, I just don't understand which to do. In my opinion, the duct work modifications are obviously due to the marijuana grow. The patch work done (post grow) in both the sheet rock and duck work match, and are obvious indicators as to where duct work ran when the marijuana grow was active.

Like stated above, after spending $6800 on a new heat pump, I cannot afford anymore repairs. The nest seems to keep the home more comfortable, while not using auxiliary heat which should be saving me money.

I still can't help ponder the benefits to removing the 25x14 air return in the basement.

Leaving a 14x14 return and a single 6" supply for 598sqft seems logical to me. It also seems to reason it would pull more air from the 24x24 in my living area, in turn keeping my living area more comfortable. Once again, the installers seemed less than interested in any of this.

I am hesitant to make modifications without knowledge of exactly the effects on the efficiency of my system.

All I am trying to do is ensure my living area is maintained in the most efficient manner possible.
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Old 03-17-2014, 09:14 PM   #9
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Number of air returns in home


The plus side is that the Nest looks at local temp & rh, by the info you put into the account, and the Nest, when you set it up. There are actually more settings behind the scenes that can be tweaked on the Nest. But you have to be a Certified installer to get into those.

The good thing is that due to it sees what the local temps & rh (relative humidity) is going to be, it can adjust its settings. You would need to contact a local Certified Nest installer, to have them tweak it even more, to adjust it to work even better for you.

As for the local installers. They look at it that if they are not going to make money off of the job, they do not even bother. Even though that customer looking for a installer could end up making the installer money. I would find a local mom & pop one or two guy or gal operation, that does hvac, to have them do any work you need on the system.

I use a guy that does plumbing, hvac for those two items. His family has been in the business for over a Century. Very multi-generation family in this business. Even if I just call him with a question about something, he will listen. Even if it is not a job that I need him on site to do.

If you did homeowner setup, here is the instructions to go into Pro setup, to make those extra adjustments if needed.

How do I enter pro Setup?

When you setup your Nest Learning Thermostat for the first time, you will be asked if you are a homeowner or a professional. if you answer Professional, then you will be presented with Pro Setup.

To enter Pro Setup on your Nest Learning Thermostat after the main setup, follow these steps:

Pro Setup
Go to SETTINGS > EQUIPMENT > CONTINUE > CONTINUE > PRO SETUP

Read the disclaimer, and if you are an installation professional, continue from there, you can turn the ring to select each of the wires connected to your Nest Thermostat. Click to select one. You can set and change the source type (e.g. Gas, Electric, Oil) and the delivery type (e.g. forced air, in-floor radiant). Once you validate your changes, this wire will be highlighted in green while the wires you haven’t set yet remain in yellow.

Once you are done with the advanced configuration, click DONE > CONTINUE > DONE.
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Old 03-19-2014, 09:37 PM   #10
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any other ideas? I'm getting tempted to do some self tests now that I have this nest. I can get online and monitor everything about its usage throughout the day. Seems I could get my own answer to this question.
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Old 03-19-2014, 10:05 PM   #11
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Number of air returns in home


What's the issue? Too cold, too hot? The number of returns doesn't matter if you are comfortable.

Hopefully one of the pros will stop by.
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Old 03-19-2014, 10:20 PM   #12
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What's the issue? Too cold, too hot? The number of returns doesn't matter if you are comfortable.
No issue. Mainly curiosity and understanding.

I can't make sense of the necessity of larger return space in a walkout basement than the living quarters. I am fine with it, if that's how it is supposed to be. It just doesn't seem logical to me.

I get the air circulation and understand there should be a return down there. But two? For such a small space?

The answer is most likely I am just not knowledgeable of HVAC. I enjoy learning. I have posted here in search information to better understand. That is all.

Had the duct never been modified and the home previously used for the primary use of marijuana growing, this would have never concerned me. But now I just can't help but think that my system could run more EFFICIENTLY with proper duct work.

My understanding of airflow is the path of least resistance. So if the returns in my basement are too large/plentiful, wouldn't that cause less return from my living quarters? (the air handler is lower than all returns)

Also, the extra suction from return has to put some sort of strain on the single supply to the area? Or at least cause air to be drawn in from my crawlspace (which I would think would be bad).
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Old 03-20-2014, 07:11 AM   #13
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Bear in mind I'm not an HVAC pro. If the basement return can't get enough air it's going to pull it from upstairs or other leaks in the structure and pull more air from the other returns. IMO if you are comfortable and your electricity bill isn't through the roof, don't over think it.
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Old 03-20-2014, 10:43 AM   #14
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Number of air returns in home


I have a two level home (one is a north facing walk-out) with 3 - 6x16 (approx.) returns on the lower level and wish I had one more for uniformity. We have on open stairway (almost a chimney) and no way to zone the place.

In the winter, I run the furnace fan 24/7 and the ECM variable speed fan is quiet and cheap to run. I usually crank down some upstairs supply registers and open the downstairs supplies. Having vaulted ceiling in the upstairs make bit of a problem, but I have ceiling fans to circulate. The open stair acts like a chimney. - Two north facing over-size sliding doors really do not make for problems in the winter because they are good quality and professionally installed (I paid the $800 to take the certified window installer class for other purposes) and I could not find a single fault. I was not up to tearing out and disposing of the doors and wrestling with everything, especially the upper level and the installer had the experience and materials for the pan flashing.

In the summer, I do the opposite and run the fan on automatic to get maximum humidification. The upper supplies are opened wide and the downstairs are throttled down for comfort.

In MN (up to 100F in summer and down to -25F in the winter), my cooling costs are slightly higher than my maximum heating costs. Furnace (4 years old) is 85% efficient and the AC is an older unit, so the efficiency may not be high as it could be, but not enough to justify replacement. Our major ceiling fan upstairs has been running 24/7 for about 5 years on low, but can easily be reversed.

This is just a different situation, but it works and some of the ideas can be related to other situations and life styles.

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Old 03-28-2014, 08:34 PM   #15
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Bear in mind I'm not an HVAC pro. If the basement return can't get enough air it's going to pull it from upstairs or other leaks in the structure and pull more air from the other returns. IMO if you are comfortable and your electricity bill isn't through the roof, don't over think it.
I do have a problem with over thinking situations. Bill was high but I think the problem was due to thermostat. This nest with aux lockout has seemed to keep KWH much lower than previous thermostat. The previous one called AUX heat after only .5 degree temp swing. Even after adjusting it to 1 degree swing the initial cycling of the system seemed to always want to call AUX heat to assist heat pump.

Winter pretty much over so unfortunately I wont be able to do much testing. I think I will just ride the year out and compare KWH usage from previous bills to this new year to determine how a 10seer 3.5 ton compares to a 14 seer 4 ton. I was hoping the new TRANE would save money each month.....

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