Author Topic: Second Floor Air Conditioning Issue  (Read 1316 times)

Mr. Freedom

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Second Floor Air Conditioning Issue
« on: May 27, 2020, 08:06:30 PM »
Iíve been in my two-story house about 10 years now.  The second floor always had issues with cooling down in the summer (Iím in the Midwest).  Iíve paid some hefty electric bills in the past trying to cool down that second floor with the one thermostat we had on the main floor.  Thereís 4 of us who sleep on the second floor in 3 bedrooms Ė my wife and I in the master bedroom (18' x 16í) and two school-aged kids who each have their own rooms (about 15' x 12í each).

About 7 years ago we had our basement finished and I decided to have a zone air conditioning system put in for the basement, main floor and second floor hoping that being able to target the second floor at night would help solve the issue.  The project was completed in late fall so we werenít using the air conditioning around that time so we didnít know if helped. 

It turned out that it didnít help and when I had another warranty HVAC person come out and examine what the problem was I learned that the original air duct that goes from the basement to the second floor is not wide enough to accommodate the amount of cold air pressure that is attempting to be pushed up the duct by our air conditioning unit.  A couple of different HVAC people looked at it and concluded the same thing.  I donít recall the specific quotes they gave to try to put in a wider duct to correct the issue but the cost was really out of the question and it would have been a major project.  Plus, the duct runs up from the basement to the second floor alongside one wall that is opposite of the side of the house where our master bedroom is so I was told that the distance the air has to be pushed horizontally once it gets to the second floor to reach our room was also probably a contributing issue.  I donít even run the zone system thermostat for the second floor at all anymore as at most it gets just a little cooler after running for a long time than if just the main floor thermostat is used but it really jacks up my electric bill substantially. 

About 3 years ago I go into living an FI lifestyle and slashed my energy bills in general, but the accommodation we have been making for hot and humid summer nights over the past couple years is that family members will tend to sleep on a mattress on the main floor or we have some decent cots set up in the finished basement which has worked OK.  As the kids have gotten a little older this has become less of a palatable solution and everyone would generally prefer to sleep in their own beds. 

I want to explore some other potential solutions that wonít result in an exorbitant electric bill if possible.  About 6 years ago we did try a portable air conditioner in our master bedroom with an exhaust hose and panel that connected to the window.  This unit cost a few hundred dollars at the time.  We tried it for a few days but it turned out to be way too loud and I returned it.  I was not very cost conscious at the time either so I donít know how much that unit would have added to electric bill monthly. 

Another thing that I think is a problem for this issue is that our second floor design is partially open to the first floor (see photo).  So thereís the master bedroom that opens out into an exposed stairway area that extends down to the first floor and then thereís a hallway that goes around a corner on the second floor to our two kidsí rooms.  We just need those three rooms on the second floor cooled.  There is a fourth bedroom that is used as a rec room.  For this cooling issue, itíd be nice if the 2nd floor was more closed off without that exposed area around the stairs that opens up to the first floor where perhaps we otherwise could have some kind of portable unit aid in cooling more than one room.  The kidsí rooms are adjacent to each other, although they would both strongly prefer to have their doors closed at night. 

Iíve started to research portable units again but Iím not really sure what Iím looking at or for.  The ideal solution in my mind with this being an area I admittedly donít know much about would be to have 3 separate air units (hopefully smaller units for my kids' relatively smaller rooms), one for each room at night with our doors closed and then we could actually set the thermostat higher or off on the main floor during the night to save money there to offset the cost of running the separate portable units.  I would think that having 3 units running is going to be pretty costly to my energy bill, but it probably would actually work if they make them somewhat quieter now.

Any input, insight or suggestions that could be offered would be appreciated.

Thank you!

brooklynmoney

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Re: Second Floor Air Conditioning Issue
« Reply #1 on: May 27, 2020, 09:15:25 PM »
This is not my area of expertise except I can say with confidence a room AC that you put in the window works well. For about 15 years I lived in 4th floor apartments with no central AC so this I know.

justinramani

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Re: Second Floor Air Conditioning Issue
« Reply #2 on: May 27, 2020, 09:19:35 PM »
Why not look into having a mini split installed?


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Mr. Freedom

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Re: Second Floor Air Conditioning Issue
« Reply #3 on: May 28, 2020, 06:12:56 AM »
Thanks a lot for recommendation of the mini split system and also vouching for the effectiveness of a room AC unit.  I'm going to continue to explore what options there may be for room units.  I looked at an installation video on the mini split systems and I see that it involves going through the wall to the outside of the house and connecting to the existing AC unit.  Doing that for 3 rooms would be a lot.  I won't rule it out completely but will see what I could make work with portable or window unit AC systems. 

Thank you!   

BudgetSlasher

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Re: Second Floor Air Conditioning Issue
« Reply #4 on: May 28, 2020, 06:29:20 AM »
A few thoughts ...

Long term, I would consider a mini-split system. I've avoided installing them here only because I would want heat to a very low temperature, which adds greatly to the cost. If you need only AC or limited heat this might be something to look at.

We have 2 window units. They are cheap and second hand. They may or may not be energy efficient. In the last 5 years we have maybe used them for a total of 2 weeks (and usually only one in master bedroom).

If you are going to get the floor models, which is great to not have to lift or worry about dropping, make sure you get one that has two hoses (not 1). The versions with a single hose take air from the room they are in use it in their operation and exhaust it outside. This puts the house under negative pressure and outside air (possibly warm and wet) will find its way into your house elsewhere. The second hose takes the air from outside rather than inside and avoids the negative pressure situation.

The house I grew up in have a central (atic) exhaust fan. That thing could move an insane amount of air very quickly when it was set to high. It allowed us to close the house up during the day, open the windows when thing cooled down at night and quickly change the air in the house.

In our current house we added central dehumidification. Just doing this made temperature warmer temperatures feel cooler. In fact nights that we used to open the windows, we now leave them closed because the dryer air is more comfortable than the outside air that is cooler and wetter. (we used to open the windows every night, now it is once or twice a week).

As for your house ... hot air rises and being open to below probably doesn't help. If your return duct (or primary return duct) is upstairs it would only make matters worse. It sounds like you HVAC system was originally designed by rule of thumb; there are all kinds of calculations (called manuals) that determine how much heat/cooling is need, how big the ducts need to be and where they need to be place (I looked into it when addressing our heat needing more return grate area and it approaches JFM).

BudgetSlasher

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Re: Second Floor Air Conditioning Issue
« Reply #5 on: May 28, 2020, 06:32:18 AM »
Thanks a lot for recommendation of the mini split system and also vouching for the effectiveness of a room AC unit.  I'm going to continue to explore what options there may be for room units.  I looked at an installation video on the mini split systems and I see that it involves going through the wall to the outside of the house and connecting to the existing AC unit.  Doing that for 3 rooms would be a lot.  I won't rule it out completely but will see what I could make work with portable or window unit AC systems. 

Thank you!   

Mini-splits generally have their own exterior unit, I doubt that it will interconnect with your current system (but it not impossible).

Depending on the system you can install only one exterior unit, go through the exterior wall only once and then have a distribution box inside. (you will need to find a way to route the condensate).


Mr. Freedom

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Re: Second Floor Air Conditioning Issue
« Reply #6 on: May 28, 2020, 07:04:01 PM »
Thanks BudgetSlasher for the education around some of those options.  I didn't know that about the floor models having a two-hose model and the advantages of that.  The more I think about this I'm just really looking for a balance between a solution that is as economical as possible and "good enough" for the temperature control.  I anticipate we'll be in this house a few years longer so if some floor models or window units work I wouldn't be altering anything permanently with the house like with the mini-split installation and I could probably sell those units for at least a little something down the road when we move.  I thought I'd go with an incremental approach and get a window unit for just our master bedroom for now and the kids for a while can sleep on the lower levels on really hot nights. Our gas/electric company does provide information if you request it as to how much energy was used on a given day so I can isolate and see how much the ac unit is using.  This has been helpful.  Thank you very much.

YttriumNitrate

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Re: Second Floor Air Conditioning Issue
« Reply #7 on: May 29, 2020, 07:05:16 AM »
I want to explore some other potential solutions that wonít result in an exorbitant electric bill if possible.  About 6 years ago we did try a portable air conditioner in our master bedroom with an exhaust hose and panel that connected to the window.  This unit cost a few hundred dollars at the time.  We tried it for a few days but it turned out to be way too loud and I returned it.  I was not very cost conscious at the time either so I donít know how much that unit would have added to electric bill monthly.

I'm in a similar situation living in the Midwest with three level house that has insufficient duct work to cool the finished attic during the heat of the summer. With the AC running, a 15-20 degree difference between the attic and the basement was not unusual. I looked into mini-splits, and adding duct blowers to move air from the basement to the attic, but ultimately we just use fans in the attic for as long as possible and then switch over to two window AC units for July and August.

Stay away from those portable AC units with an exhaust hose as they tend to be inefficient and noisy.
https://www.youtube.com/watch?v=_-mBeYC2KGc

BudgetSlasher

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Re: Second Floor Air Conditioning Issue
« Reply #8 on: May 29, 2020, 07:22:20 AM »
Two non-HVAC avenue to investigate.

Look into how well your attic is insulated/air sealed and whether adding additional insulation (such as blow in cellulose) in addition to the existing insulation might help.

I cannot tell you how much a ceiling fan and moving air helps one "feel" cooler. Perhaps you could some on the bedrooms. f you do you do not need to leave them on 24/7; they don't make it cooler then moving air just help people feel cooler (no people in the room and this goes away).

A second train of thought occurs to me; swamp (evaporative) coolers. I know they exist in various forms and have met people who swear by them, but I have always lived in places with higher humidity (which is not ideal for a swamp cooler). If you live in a dry climate it might be worth looking into.

EricEng

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Re: Second Floor Air Conditioning Issue
« Reply #9 on: June 02, 2020, 12:28:19 PM »
Why not look into having a mini split installed?


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This looks to be the best solution for this situation with the open 2nd floor.  That or a window unit.  Those portable units with a hose are horrendously inefficient.  Much of the world lives off mini splits and keeps costs down by only cooling when you are in the room.  Minisplits are pretty quite.  I've also used window units in the past, noisy but for sleeping fine.

index

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Re: Second Floor Air Conditioning Issue
« Reply #10 on: June 03, 2020, 08:15:56 AM »
If the window units are too loud look for window units with inverter technology. This allows them to scale their power draw and compressor noise. A 12k btu unit may modulate down to 3000 BTU, sipping power, quite, dehumidifying, and enough cool air to maintain temperature. This is the same way mini splits work.

https://www.homedepot.com/p/LG-Electronics-14-000-BTU-115-Volt-Dual-Inverter-Smart-Window-Air-Conditioner-in-White-with-Wi-Fi-Enabled-and-Remote-LW1517IVSM/303947186

This one is from the world's largest AC manufacturer and allows you to close your window:

https://www.amazon.com/Midea-Inverter-Conditioner-Flexibility-Installation/dp/B08677DCKN

This is probably the smallest option:

https://www.kapsulair.com/

ReadySetMillionaire

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Re: Second Floor Air Conditioning Issue
« Reply #11 on: June 04, 2020, 07:45:21 AM »
Interesting that you are also having this problem. I just moved into a two story house and the temperature difference from the first floor to the second floor is about 10 degrees (I know this because we have a baby monitor upstairs that has a temperature reading).

So far I tried the following relatively easy remedies:

1) I closed all the vents on the first floor. This has noticeably improved air flow upstairs. The cool air gets back down there anyway.

2) We already bought "sun zero" blinds (they are like $10 when they're on sale, and they completely block out light). We keep these closed during the day.

3) Sleep with just sheets! I don't know why more people don't do this. It feels great.

4) We bought cheap floor fans. We might eventually get ceiling fans but we're working on a bunch of other stuff.

The upstairs is now pretty tolerable. The hottest it gets during the day is 78 degrees and it usually cools down to low 70s, high 60s at night. It's been very tolerable. I too am in the Midwest so it will probably be like this late May to August every year.

BudgetSlasher

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Re: Second Floor Air Conditioning Issue
« Reply #12 on: June 04, 2020, 07:56:30 PM »
Interesting that you are also having this problem. I just moved into a two story house and the temperature difference from the first floor to the second floor is about 10 degrees (I know this because we have a baby monitor upstairs that has a temperature reading).

So far I tried the following relatively easy remedies:

1) I closed all the vents on the first floor. This has noticeably improved air flow upstairs. The cool air gets back down there anyway.

2) We already bought "sun zero" blinds (they are like $10 when they're on sale, and they completely block out light). We keep these closed during the day.

3) Sleep with just sheets! I don't know why more people don't do this. It feels great.

4) We bought cheap floor fans. We might eventually get ceiling fans but we're working on a bunch of other stuff.

The upstairs is now pretty tolerable. The hottest it gets during the day is 78 degrees and it usually cools down to low 70s, high 60s at night. It's been very tolerable. I too am in the Midwest so it will probably be like this late May to August every year.

Item 1 isn't a really great long term solution.

HVAC should be (but often isn't) designed with a balance between return and supply. Closing half the supply vents throws off the balance and could result in higher electric usage as the fan struggles to deal with the imbalance.

ReadySetMillionaire

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Re: Second Floor Air Conditioning Issue
« Reply #13 on: June 05, 2020, 07:48:35 AM »
Interesting that you are also having this problem. I just moved into a two story house and the temperature difference from the first floor to the second floor is about 10 degrees (I know this because we have a baby monitor upstairs that has a temperature reading).

So far I tried the following relatively easy remedies:

1) I closed all the vents on the first floor. This has noticeably improved air flow upstairs. The cool air gets back down there anyway.

2) We already bought "sun zero" blinds (they are like $10 when they're on sale, and they completely block out light). We keep these closed during the day.

3) Sleep with just sheets! I don't know why more people don't do this. It feels great.

4) We bought cheap floor fans. We might eventually get ceiling fans but we're working on a bunch of other stuff.

The upstairs is now pretty tolerable. The hottest it gets during the day is 78 degrees and it usually cools down to low 70s, high 60s at night. It's been very tolerable. I too am in the Midwest so it will probably be like this late May to August every year.

Item 1 isn't a really great long term solution.

HVAC should be (but often isn't) designed with a balance between return and supply. Closing half the supply vents throws off the balance and could result in higher electric usage as the fan struggles to deal with the imbalance.

I've read this and was told by an HVAC friend to just keep the fan "on" instead of "auto." Any thoughts?

Papa bear

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Re: Second Floor Air Conditioning Issue
« Reply #14 on: June 05, 2020, 08:42:30 AM »
Interesting that you are also having this problem. I just moved into a two story house and the temperature difference from the first floor to the second floor is about 10 degrees (I know this because we have a baby monitor upstairs that has a temperature reading).

So far I tried the following relatively easy remedies:

1) I closed all the vents on the first floor. This has noticeably improved air flow upstairs. The cool air gets back down there anyway.

2) We already bought "sun zero" blinds (they are like $10 when they're on sale, and they completely block out light). We keep these closed during the day.

3) Sleep with just sheets! I don't know why more people don't do this. It feels great.

4) We bought cheap floor fans. We might eventually get ceiling fans but we're working on a bunch of other stuff.

The upstairs is now pretty tolerable. The hottest it gets during the day is 78 degrees and it usually cools down to low 70s, high 60s at night. It's been very tolerable. I too am in the Midwest so it will probably be like this late May to August every year.

Item 1 isn't a really great long term solution.

HVAC should be (but often isn't) designed with a balance between return and supply. Closing half the supply vents throws off the balance and could result in higher electric usage as the fan struggles to deal with the imbalance.

I've read this and was told by an HVAC friend to just keep the fan "on" instead of "auto." Any thoughts?
So I thought the same thing. Run the fan! Keep circulating the cold air!

Except it doesnít dehumidify well.  You need to be able to let the water that condensed on the evaporator coils to run off, rather than be blown back through the house.

Iíve had tenants who had their floors swell due to this problem.  Turn the fan to auto, and the problem is fixed. 


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SuperSecretName

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Re: Second Floor Air Conditioning Issue
« Reply #15 on: June 05, 2020, 09:15:44 AM »
no idea if this is a good idea or not, but what about a whole house fan in the attic?  That could draw the warm air outside of the upstairs.

BudgetSlasher

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Re: Second Floor Air Conditioning Issue
« Reply #16 on: June 06, 2020, 09:49:13 AM »
Interesting that you are also having this problem. I just moved into a two story house and the temperature difference from the first floor to the second floor is about 10 degrees (I know this because we have a baby monitor upstairs that has a temperature reading).

So far I tried the following relatively easy remedies:

1) I closed all the vents on the first floor. This has noticeably improved air flow upstairs. The cool air gets back down there anyway.

2) We already bought "sun zero" blinds (they are like $10 when they're on sale, and they completely block out light). We keep these closed during the day.

3) Sleep with just sheets! I don't know why more people don't do this. It feels great.

4) We bought cheap floor fans. We might eventually get ceiling fans but we're working on a bunch of other stuff.

The upstairs is now pretty tolerable. The hottest it gets during the day is 78 degrees and it usually cools down to low 70s, high 60s at night. It's been very tolerable. I too am in the Midwest so it will probably be like this late May to August every year.

Item 1 isn't a really great long term solution.

HVAC should be (but often isn't) designed with a balance between return and supply. Closing half the supply vents throws off the balance and could result in higher electric usage as the fan struggles to deal with the imbalance.

I've read this and was told by an HVAC friend to just keep the fan "on" instead of "auto." Any thoughts?

I haven't tried that method in a cooling dominated climate. I did for a time try in a heating dominated climate. I didn't like it for a couple reasons; it was louder than the heat (the fan tends to have different speeds for fan, heat, AC) and the electric usage (my heat only tended to run in the morning and evening and was mostly idle when we were sleeping or at work) all that extra fan time added up.

BudgetSlasher

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Re: Second Floor Air Conditioning Issue
« Reply #17 on: June 06, 2020, 09:57:07 AM »
Interesting that you are also having this problem. I just moved into a two story house and the temperature difference from the first floor to the second floor is about 10 degrees (I know this because we have a baby monitor upstairs that has a temperature reading).

So far I tried the following relatively easy remedies:

1) I closed all the vents on the first floor. This has noticeably improved air flow upstairs. The cool air gets back down there anyway.

2) We already bought "sun zero" blinds (they are like $10 when they're on sale, and they completely block out light). We keep these closed during the day.

3) Sleep with just sheets! I don't know why more people don't do this. It feels great.

4) We bought cheap floor fans. We might eventually get ceiling fans but we're working on a bunch of other stuff.

The upstairs is now pretty tolerable. The hottest it gets during the day is 78 degrees and it usually cools down to low 70s, high 60s at night. It's been very tolerable. I too am in the Midwest so it will probably be like this late May to August every year.

Item 1 isn't a really great long term solution.

HVAC should be (but often isn't) designed with a balance between return and supply. Closing half the supply vents throws off the balance and could result in higher electric usage as the fan struggles to deal with the imbalance.

I've read this and was told by an HVAC friend to just keep the fan "on" instead of "auto." Any thoughts?
So I thought the same thing. Run the fan! Keep circulating the cold air!

Except it doesnít dehumidify well.  You need to be able to let the water that condensed on the evaporator coils to run off, rather than be blown back through the house.

Iíve had tenants who had their floors swell due to this problem.  Turn the fan to auto, and the problem is fixed. 


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That sounds less like an issues with the fan being always on and more like an issue that the "always on" fan speed was different from (and overrode) the "AC" fan speed. As I understand it, in case like that where the air contact time with the coils in changed the dehumidification rate can be (also an oversized AC can cause this).

An older system may be able to setup up so that the "Always on" and "AC" speeds are the same. Some modern systems also have a ultra low speed for maintaining air circulation in the house or for keep air flowing over high efficency air filters. (the fancy ECM motor I put in my air handler has wires for something like 5 fan speeds.


index

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Re: Second Floor Air Conditioning Issue
« Reply #19 on: June 09, 2020, 07:29:37 AM »
we have the same problem. Trying this next:

https://www.acinfinity.com/home-ventilation/register-booster-fans/available-soon-pre-order-now-airtap-t4-quiet-register-booster-fan-system-white-for-4-x-12-registers/

another possibility
https://www.homedepot.com/p/Suncourt-Flush-Fit-Register-Booster-Fan-in-White-HC500-W/202803685

Those register fans end up sucking air from upstream registers rather than cool air from the source. If they are on the last register in a run, they help, but rob from the downstream registers. 

ReadySetMillionaire

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Re: Second Floor Air Conditioning Issue
« Reply #20 on: June 09, 2020, 08:55:19 AM »
My takeaway from this thread is that HVAC systems suck in two story houses and I'm just going to have to deal with it moving forward.  I'm fine with that; my wife probably not so much.

zolotiyeruki

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Re: Second Floor Air Conditioning Issue
« Reply #21 on: June 12, 2020, 09:30:52 AM »
My takeaway from this thread is that HVAC systems suck in two story houses and I'm just going to have to deal with it moving forward.  I'm fine with that; my wife probably not so much.
I'd amend this to say "HVAC in home with two-story rooms is hard," and "a builder who uses a single HVAC system for a two-story house is cheaping out."

BudgetSlasher

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Re: Second Floor Air Conditioning Issue
« Reply #22 on: June 12, 2020, 04:56:33 PM »
My takeaway from this thread is that HVAC systems suck in two story houses and I'm just going to have to deal with it moving forward.  I'm fine with that; my wife probably not so much.
I'd amend this to say "HVAC in home with two-story rooms is hard," and "a builder who uses a single HVAC system for a two-story house is cheaping out."

I'd agree with the first statement, but, with the proper design, building, sizing, layout, and manual j/d calculations, I would not say 2 units for a two story house are always necessary.

BudgetSlasher

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Re: Second Floor Air Conditioning Issue
« Reply #23 on: June 12, 2020, 05:01:27 PM »
To the original post, you could also consider a smart thermostat.

I have an ecobee and it has 2 features that might be of interest to you.

1) You can add wireless room sensors that can sense if a room is occupied. The thermostat can also be configured to use or no use certain sensors during home/away/sleep. We have three plus the thermostat which are in our living room (thermostat), living room, 2nd bedroom, and upstairs bonus room. When the sensor is selected for a time period (and in our case we have been in the room recently) it will average them.

2) You can select an amount of time an hour for the fan to run (I believe the run time is randomized). We do not do this as our central unit is heating only and hot air rises ... so we stay pretty constant during the winter.

Villanelle

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Re: Second Floor Air Conditioning Issue
« Reply #24 on: June 12, 2020, 05:31:50 PM »
A mini-split need not connect to your current system.  In fact, that is the beauty fo them.  I've lived in two homes that had only mini-splits--no central air or heating. 

You could consider installing only in your master and then allowing the central system to cool the other upstairs rooms.  Perhaps taking that one large room off the system would allow the current ducting to accommodate the remaining smaller space.  That seems like the least drastic, least expensive option.

A portable unit would cost less initially, but is less efficient.  We have one in our rental and getting a decent seal around it is nearly impossible.  You also lose the ability to open and close that window when the unit is installed, and it puts off a frustrating amount of heat, actually.  I've wrapped the ducting tube (which connects to the piece that fits into the window, out of which the hot wet air is vented) in batting which does help keep the heat from radiating back into the room we are trying to cool. 

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Re: Second Floor Air Conditioning Issue
« Reply #25 on: June 14, 2020, 12:24:19 AM »
I cool my entire house with mini-splits and am very happy with them, but I don't think they're the answer for you.  If you are only likely to be in the house for a  few years, I'd go with inexpensive window units in the upstairs bedrooms.  I'd run them for an  hour or two before going to sleep or just set the thermostat to a comfortable temperature and maybe spring for a few floor fans or ceiling fans to move the air around.  The window units will be inefficient, but they are inexpensive and if you are only running them for a few hours a night during the Summer months, the electrical costs shouldn't be too bad.  If you are going to be in the house for the long-term, the higher cost for a more efficient, quieter mini-split system might make more sense. 

better late

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Re: Second Floor Air Conditioning Issue
« Reply #26 on: June 23, 2020, 08:32:01 PM »
we have the same problem. Trying this next:

https://www.acinfinity.com/home-ventilation/register-booster-fans/available-soon-pre-order-now-airtap-t4-quiet-register-booster-fan-system-white-for-4-x-12-registers/

another possibility
https://www.homedepot.com/p/Suncourt-Flush-Fit-Register-Booster-Fan-in-White-HC500-W/202803685

Those register fans end up sucking air from upstream registers rather than cool air from the source. If they are on the last register in a run, they help, but rob from the downstream registers.

Tried the ACinfinity version and itís AWESOME. Has lowered the temperature dramatically in our 2nd floor bedroom. It is the last register in the run and I donít care thatís itís taking cold air from downstairs- thats the whole idea. Some nights I pull a comforter up from the foot of the bed to take the chill off. Issue solved!

EricEng

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Re: Second Floor Air Conditioning Issue
« Reply #27 on: June 29, 2020, 11:14:08 AM »
My takeaway from this thread is that HVAC systems suck in two story houses and I'm just going to have to deal with it moving forward.  I'm fine with that; my wife probably not so much.
I'd amend this to say "HVAC in home with two-story rooms is hard," and "a builder who uses a single HVAC system for a two-story house is cheaping out."
And they can still screw it up like my home.  Two story with separate ACs.  However, they put the thermometer control in a loft that is open to the first floor.  So heat rises into loft activating loft thermostat while cold air pumps into all the bedrooms which have closed doors (keep out sunlight and noise with sleeping babies).  Then once loft eventually somehow manages to cool off, it stops and stays cool while bedrooms all heat up from people in them.  Result is icy bedrooms when you go to sleep, and ovens by 2-3am.  Thermostat in master bedroom would have fixed that and was the original home design but builder moved it right before drywall.

BudgetSlasher

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Re: Second Floor Air Conditioning Issue
« Reply #28 on: June 29, 2020, 07:09:53 PM »
My takeaway from this thread is that HVAC systems suck in two story houses and I'm just going to have to deal with it moving forward.  I'm fine with that; my wife probably not so much.
I'd amend this to say "HVAC in home with two-story rooms is hard," and "a builder who uses a single HVAC system for a two-story house is cheaping out."
And they can still screw it up like my home.  Two story with separate ACs.  However, they put the thermometer control in a loft that is open to the first floor.  So heat rises into loft activating loft thermostat while cold air pumps into all the bedrooms which have closed doors (keep out sunlight and noise with sleeping babies).  Then once loft eventually somehow manages to cool off, it stops and stays cool while bedrooms all heat up from people in them.  Result is icy bedrooms when you go to sleep, and ovens by 2-3am.  Thermostat in master bedroom would have fixed that and was the original home design but builder moved it right before drywall.

If thermostat placement is the only issue, I suggest a smart thermostat. My Ecobee3 allow for battery powered remote sensors to be used.

Ripple4

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Re: Second Floor Air Conditioning Issue
« Reply #29 on: June 30, 2020, 08:18:28 AM »
Quote

I've read this and was told by an HVAC friend to just keep the fan "on" instead of "auto." Any thoughts?

I would suggest installing an energy efficient HVAC blower motor before doing this. the permanent split capacitor 'PSC' motor in older units are horribly inefficient, it will cost roughly 8 cents an hour to run all the time, or $56/month. Contrasted to the ~$150 MARS 10860 1/2hp azrure EC motor (electronically commuted motor) will reduce the power usage from 900VA/650watts to 240VA/240W (at full speed) and it has an 'always on' lowest speed that circulates the air constantly while sipping only 30 watts ($3/month). This will help the OP with undersized runs. as I understand it, as of 7/2019 all furnaces have to have ECM motors to be energy star.

on the idea about closing all the vents first floor, i think that will cut down the total airflow in the HVAC unit too much its better to leave it all wide open and solve the issue another way. Also putting a digital thermometer in the vent and verifying that the cool air is 15F lower than the air return temperature and also making sure the AC is running for between 10 and 15 minutes at a time are rules of thumb for AC system health. some thermostats also allow setting how many times the system will cycle per hour, i have mine set to 2 cycles so that it runs longer when it does come on.

so much good advice here, recapping: R50 attic insulation, penetration sealing in the attic, black out curtains, all these are under $1000 total for DIY. then avoiding portable AC units but embracing inverter-based mini-splits or window units. And I would add dollar store automotive sun reflectors in East, south and west facing windows, but especially west facing windows.

I had the same issues >12F difference between the upstairs and downstairs in the summer and a $200+/month bill to show for it, the stated upgrades have reduced this to 2F, and a power bill that is MUCH less. I also check the weather and if its going to be cooler than about 74F and not too humid or raining, then I open the windows at 10pm and close them at 9am with window fans to pull in the cool night air, why pay for what nature sometimes gives for free.

EricEng

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Re: Second Floor Air Conditioning Issue
« Reply #30 on: June 30, 2020, 09:18:49 AM »
If thermostat placement is the only issue, I suggest a smart thermostat. My Ecobee3 allow for battery powered remote sensors to be used.
We have a wired smart thermostat.  Attic has lots of space, so I can probably just rerun the wires when I find time.

BudgetSlasher

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Re: Second Floor Air Conditioning Issue
« Reply #31 on: June 30, 2020, 06:14:02 PM »
If thermostat placement is the only issue, I suggest a smart thermostat. My Ecobee3 allow for battery powered remote sensors to be used.
We have a wired smart thermostat.  Attic has lots of space, so I can probably just rerun the wires when I find time.

That might be the cheapest.

Our Ecobee allows for multiple sensors to be used (or excluded) base on the heating/ cooling cycle (such as sleep) and room occupancy; we've left the wired thermostat in the living room, but have sensors in our bedroom, the second bedroom, and the TV room (2 on the first floor and 2 on the second floor). At least in the winter it helps to even things out (it might in the summer if we had central AC). With the multiple sense it does some form of math (doesn't always seem to be a straight average).

NaN

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Re: Second Floor Air Conditioning Issue
« Reply #32 on: July 01, 2020, 08:10:19 AM »
I had a friend who had similar issues on a two story house. He had played around with the registers. He just recently played around with closing off a return air vent on his first story. He has claimed it has improved, and it got me thinking.

It seems possible in these situations the return air on the first story and basement are overpowering the return air upstairs. The cold air dominates on the lower floors for a lot of reasons, pushing hot air up. Further, because hot air rises and it goes up to your second story, the pressure will be further increasing upstairs, making it harder for the upstairs supplies to work. Yes, higher pressure should mean the upstairs returns should work  better, but the downstairs returns might just be overpowering.

Do you have an air return upstairs such that you can play with closing off return air downstairs? I also agree with ceiling fans upstairs blowing down. You need to make it easier for the supply air to go up, as well as for the hot air in the house to be pulled back through the air return. Check out these guys. https://www.bigassfans.com/fans/   These guys are actually pretty smart with a lot of designers with science backgrounds. You could easily put one of the smaller beasts (i6) up on your ceiling there above the stairs.