Adding a second A/C unit to cool upstairs

[Wiz02]

If some HVAC experts can answer some questions, I'd greatly appreciate it.

I have a 2 story 4 bedroom colonial with a total area of 3000 sq ft. and the upstairs is about 1200 sq ft. The house is 35 years old, with typical tract house 2x4 construction and it has a basement and attic.

Attic 2x10 floor is insulated with cellulose. There is a ridge vent and the space isn't conditioned but you can stand up once you get away from the eaves. There is only a tiny opening (about 2x2) in a closet ceiling to access the attic.

The existing hot air heat pump, just like its predecessors, works fine to cool the downstairs. The upstairs, even with ceiling fans, is uncomfortably warm at night and is becoming more uncomfortable as we get older and the summers are getting hotter. Setting thermostat to arctic downstairs doesn't really make the upstairs comfortable.

Some of my neighbors have added a second a/c system to cool the upstairs. Unfortunately, they aren't technically savvy so I can't get any detailed information from them before calling in some of the local contractors.

I know that the existing ductwork feeding the upstairs is too small but it's fine for heat and I'm not tearing up the house to run new ducts.

Here are a few questions and if you can provide any additional advice it would be welcome.

If I go with a traditional a/c system and they somehow get an air handler into the attic, the upstairs cold air returns all feed the existing system. How do they run new upstairs cold air returns? Not to mention that I am not thrilled with having an air handler in an unconditioned space.

If I go with a mini split (which is way too new of a technology for residential PA use (sarcasm). Can I run multiple heads to the 4 bedrooms and 2 bathrooms? Or will I need multiple units?

Any other a/c system type that I should consider? I know that there are high velocity duct systems but they aren't mainstream around here to my knowledge.

Thanks for looking.

 

[theoldwizard1]

If I go with a mini split (which is way too new of a technology for residential PA use (sarcasm).

This is BY FAR the best solution !

Can I run multiple heads to the 4 bedrooms and 2 bathrooms?

You can, but the price goes up quickly ! Also, multi-zone mini-split are less efficient.

Are all bedrooms in use ? Skip the bathrooms.

If you shop around, there are some decent widow units. You have to know what you are looking for,

 

[Wiz02]

This is BY FAR the best solution !

You can, but the price goes up quickly ! Also, multi-zone mini-split are less efficient.

Are all bedrooms in use ? Skip the bathrooms.

If you shop around, there are some decent widow units. You have to know what you are looking for,

Bathroom A/C is a prime requirement from SWMBO. Window shakers are a non starter too. 3 out of 4 bedrooms are used, I can't see leaving one out if I am going to have the job done.

I am afraid that a multi zone mini split will break the bank as the local hvac contractors don't install many mini splits so I can just imagine what they will charge for a multi zone.

I can handle installing a single zone multi split in the garage. Getting a little too old for a second story install.

 

[brewchief]

Mini splits are a tough go for this type of retro fit, not only do you need a bunch of heads you need wall space in each room(or ceiling cassettes) and you need a way to route linesets and drains to each head. If you can't gravity drain then you need a pump for each head and those add up fast.

Conventional air handler and ductwork can be done by adding a large filter grill return in a central hallway, the hole cut for the return can then be the access to get equipment into the attic. If the house heats Ok as is then it can be cooling only or a heat pump if some additional heat may be needed, if the second floor doesn't heat well then a furnace may need to be considered as well instead of just an air handler.

Ductwork can be fairly simple, an extended plenum and flex duct to registers cut into the ceiling. Central return and undercut the doors or add pass through returns above them. I'm not a huge fan of flex duct but if it's run properly and sealed well at each end it's not bad, trying to run metal duct though an attic and seal and insulate it properly is a very difficult task. You want the highest R value flex that you can find.

 

[Wrench97]

You'll need a larger opening to start with, and a pull down ladder would be nice to have, is there perhaps a walk in closet space where it could be installed?
Adding a attic A/C they would run vents and returns in the ceilings of the rooms with flexible ducts, you could probably get by with just turning off the existing vents from the downstairs unit and reopen in heating season.

It's all about comfort mini splits are noisier and the cooling is not equal across the room just like window units are.

Also more attic insulation may be a solution too, how much is currently there?

 

[u3b3rg33k]

If some HVAC experts can answer some questions, I'd greatly appreciate it.

I have a 2 story 4 bedroom colonial with a total area of 3000 sq ft. and the upstairs is about 1200 sq ft. The house is 35 years old, with typical tract house 2x4 construction and it has a basement and attic.

Attic 2x10 floor is insulated with cellulose. There is a ridge vent and the space isn't conditioned but you can stand up once you get away from the eaves. There is only a tiny opening (about 2x2) in a closet ceiling to access the attic.

The existing hot air heat pump, just like its predecessors, works fine to cool the downstairs. The upstairs, even with ceiling fans, is uncomfortably warm at night and is becoming more uncomfortable as we get older and the summers are getting hotter. Setting thermostat to arctic downstairs doesn't really make the upstairs comfortable.

Some of my neighbors have added a second a/c system to cool the upstairs. Unfortunately, they aren't technically savvy so I can't get any detailed information from them before calling in some of the local contractors.

I know that the existing ductwork feeding the upstairs is too small but it's fine for heat and I'm not tearing up the house to run new ducts.

Here are a few questions and if you can provide any additional advice it would be welcome.

If I go with a traditional a/c system and they somehow get an air handler into the attic, the upstairs cold air returns all feed the existing system. How do they run new upstairs cold air returns? Not to mention that I am not thrilled with having an air handler in an unconditioned space.

If I go with a mini split (which is way too new of a technology for residential PA use (sarcasm). Can I run multiple heads to the 4 bedrooms and 2 bathrooms? Or will I need multiple units?

Any other a/c system type that I should consider? I know that there are high velocity duct systems but they aren't mainstream around here to my knowledge.

Thanks for looking.

I had this issue. I zoned my system and the problem is gone.

I don't operate it to have wildly different temperatures up/down, but really to let it put the heating/cooling where it's desired.

I kept my single stage AC, replaced my 80% furnace and dying waterheater with a modcon combiboiler + ECM fancoil, and programmed airflows appropriately. oh and deleted all the previous owners attempt at being a manual D ductopus designer with a typical trunk and branch system. yes i have 11 zone valves, and if I did it again I'd do the belimos not the honeywell.

 

[danski0224]

Ductwork and equipment in the attic absolutely ***** ***. It isn't uncommon to see temperatures of 140 degrees in an attic, and the best you are going to do for readily available flex duct is R-8... and any metal ductwork needs to be insulated too. Then it has to be properly installed to get the R value, and every last bit of it has to be sealed.

You aren't going to get **** into a 24 x 24 opening.

You won't be able to get regular ductwork and register boots anywhere near the windows/outside walls without cutting open the ceilings. That's why the hacks put 8" round diffusers in the middle (or close to the middle) of the room in the ceiling... and the returns not too far away.

I did more than the job you describe (with help) for a regular job through work, but it was both floors, and the equipment is in the basement. The house had zero ductwork to start with.

It sucked, big time. I am the only person in the company that is capable of laying something like that out. It still took weeks to do (not including the copious amount of drywall repair) and there is really no way to do it by yourself. You don't want to know how much it reportedly costed.

I would tell you to seriously look into spray foaming the attic.

Unico would be the next suggestion if you are dead set on adding more equipment. This is the only thing you will get into a 24 x 24 opening. Duct layout and sizing is critical to avoid noise problems, but every last bit of info you need to install it correctly is online.

But I bet that I could fix most, if not all, of the problems with some fancy ductwork in the basement.

 

[u3b3rg33k]

Ductwork and equipment in the attic absolutely ***** ***. It isn't uncommon to see temperatures of 140 degrees in an attic, and the best you are going to do for readily available flex duct is R-8... and any metal ductwork needs to be insulated too. Then it has to be properly installed to get the R value, and every last bit of it has to be sealed.


But I bet that I could fix most, if not all, of the problems with some fancy ductwork in the basement.

100% thumbs down on an attic system.

also FWIW i did NO BYPASS on my system. deleted the bypass humidifier because they **** (and leak huge CFM even when in summer mode).

I despise bypasses.

 

[mm08822]

I wonder it the branch supply ducts were ever balanced?
Are there any manual dampers in the ductwork?

Are supply and return registers blocked by furniture?

A sketch of the ductwork with dimensions and lengths could also give a good baseline starting point.

Are the ceiling fans used frequently? I run some of mine 24/7.

 

[Mikes61]

When I had a two story house I had the same problem. In the summer, I slept downstairs where it was cooler. During the winter I went back upstairs.

 

[karoc]

Here in Tx ductwork and air handler is in attic, no basements in south. Air handlers can be purchase in cube form. Such as blower section, heating section, evap coil section etc. Register boxes in south mounted in ceiling and so is return air. But you still have deal with copper lines from evap coil to condenser plus dealing with electrical. All can be done, I’ve done it in my young days, this is lot work which will cost. Call a company to give you bid and suggestions. I know nothing about mini’s, and I wonder about life expectancy, and that’s ever changing technology

 

[Notgrownup]

You can get up to 5 zones…

 

[Wiz02]

Mini splits are a tough go for this type of retro fit, not only do you need a bunch of heads you need wall space in each room(or ceiling cassettes) and you need a way to route linesets and drains to each head. If you can't gravity drain then you need a pump for each head and those add up fast.

Conventional air handler and ductwork can be done by adding a large filter grill return in a central hallway, the hole cut for the return can then be the access to get equipment into the attic. If the house heats Ok as is then it can be cooling only or a heat pump if some additional heat may be needed, if the second floor doesn't heat well then a furnace may need to be considered as well instead of just an air handler.

Ductwork can be fairly simple, an extended plenum and flex duct to registers cut into the ceiling. Central return and undercut the doors or add pass through returns above them. I'm not a huge fan of flex duct but if it's run properly and sealed well at each end it's not bad, trying to run metal duct though an attic and seal and insulate it properly is a very difficult task. You want the highest R value flex that you can find.

Thanks for the input. Second floor heat is fine except for the one bedroom over the garage, no surprise there. Your explanation addressed my concerns about going with a conventional system.

 

[manwithtools]

You aren't going to get **** into a 24 x 24 opening

Interesting, we managed to install a 1.5 ton ducted mini split in the attic of our master suite (through a 22.5" x 22.5" opening) and then tied it into the existing ductwork. Disconnecting the ducts from the underperforming main unit that the HVAC professionals had specd for the house.

OP, check out ducted mini splits to see what options might be available to you.

 

[Wiz02]

You'll need a larger opening to start with, and a pull down ladder would be nice to have, is there perhaps a walk in closet space where it could be installed?
Adding a attic A/C they would run vents and returns in the ceilings of the rooms with flexible ducts, you could probably get by with just turning off the existing vents from the downstairs unit and reopen in heating season.

It's all about comfort mini splits are noisier and the cooling is not equal across the room just like window units are.

Also more attic insulation may be a solution too, how much is currently there?

No really good options for installing pull down stairs in an inconspicuous area, the one walk in closet is very small.

They really chiseled on the ductwork. Fiberglass board for the 2 main runs in the basement and flexible ducts everywhere else.

Cold air returns use the stud bays, no ductwork.

Interesting idea to close ducts feeding upstairs in summer and open them in winter.

Insulation has settled so I am sure that i could add some to the existing cellulose that mostly fills the 2x10 attic joists.

Thanks for the response

 

[Wiz02]

I had this issue. I zoned my system and the problem is gone.

I don't operate it to have wildly different temperatures up/down, but really to let it put the heating/cooling where it's desired.

I kept my single stage AC, replaced my 80% furnace and dying waterheater with a modcon combiboiler + ECM fancoil, and programmed airflows appropriately. oh and deleted all the previous owners attempt at being a manual D ductopus designer with a typical trunk and branch system. yes i have 11 zone valves, and if I did it again I'd do the belimos not the honeywell.

I believe that the root cause of poor cooling in my upstairs is that the ducts are too small and they used flexible ducts everywhere but the main supply and return ducts in the basement which are fiber board.

Can you explain how new equipment solved your problem? My heatpump with propane gas furnace backup keeps the downstairs comfortable and the upstairs too in heating season. In the summer the downstairs is comfortable but the upstairs is too hot. I believe that the existing equipment has the capacity, but is constrained by the ductwork. How did you add 11 zones?

Thanks

 

[Wiz02]

Ductwork and equipment in the attic absolutely ***** ***. It isn't uncommon to see temperatures of 140 degrees in an attic, and the best you are going to do for readily available flex duct is R-8... and any metal ductwork needs to be insulated too. Then it has to be properly installed to get the R value, and every last bit of it has to be sealed.

You aren't going to get **** into a 24 x 24 opening.

You won't be able to get regular ductwork and register boots anywhere near the windows/outside walls without cutting open the ceilings. That's why the hacks put 8" round diffusers in the middle (or close to the middle) of the room in the ceiling... and the returns not too far away.

I did more than the job you describe (with help) for a regular job through work, but it was both floors, and the equipment is in the basement. The house had zero ductwork to start with.

It sucked, big time. I am the only person in the company that is capable of laying something like that out. It still took weeks to do (not including the copious amount of drywall repair) and there is really no way to do it by yourself. You don't want to know how much it reportedly costed.

I would tell you to seriously look into spray foaming the attic.

Unico would be the next suggestion if you are dead set on adding more equipment. This is the only thing you will get into a 24 x 24 opening. Duct layout and sizing is critical to avoid noise problems, but every last bit of info you need to install it correctly is online.

But I bet that I could fix most, if not all, of the problems with some fancy ductwork in the basement.

Thanks for the response. I do realize that equipment/ductwork in the attic is not optimal to say the least and I expect that an access point will need to be added in the upstairs hall which my wife will hate, if an air handler is installed in the attic

Can you elaborate on your fancy ductwork statement the basement?

Thanks.

 

[Wiz02]

I wonder it the branch supply ducts were ever balanced?
Are there any manual dampers in the ductwork?

Are supply and return registers blocked by furniture?

A sketch of the ductwork with dimensions and lengths could also give a good baseline starting point.

Are the ceiling fans used frequently? I run some of mine 24/7.

I know that the system hasn't been properly balanced and there is only one manual damper on the flex duct that feeds a tiny downstairs powder room.

All returns are up high on the walls and aren't blocked. Floor vents aren't blocked.

I can do an accurate sketch for the downstairs ductwork which of course is less of a concern. Of course the upstairs is much harder to do.

My wife is the queen of ceiling fans. I have installed ceiling fans in nearly every room and the upstairs ceiling fans run 24 x 7 during cooling season.

 

[Wiz02]

You can get up to 5 zones…

I even found a 6 zone system, but the drains, pipes and electrical are going to make this an expensive proposition. I was planning on installing a mini split in the garage myself but I am getting too old to install a multi zone system in the attic.

 

[Wiz02]

Interesting, we managed to install a 1.5 ton ducted mini split in the attic of our master suite (through a 22.5" x 22.5" opening) and then tied it into the existing ductwork. Disconnecting the ducts from the underperforming main unit that the HVAC professionals had specd for the house.

OP, check out ducted mini splits to see what options might be available to you.

Thanks for the tip. I have lots of questions about tying into the existing ductwork. Are you using the ducted mini split for both heating and cooling or just cooling. Is it only used in the master or other rooms too?

 

[inphx]

I do like mini splits. if the head can mount through an exterior wall and the line/wire/drain ducting is not too much of an eyesore the way to save money is to get all the physical heads mounted, linesets/wire/condensate line drilled through the wall and seems like two multizone condensers on the slabs or wall mount with power ran. The job would be easier if you rent an articulating lift. A 'cheat pass' around here is the real equipment rental places charge one day for a weekend rental - and also if its a 3 day weekend. I would leave flaring and completing the line set bends at the heads to a paid tradesperson and they can evacuate the lines properly. I am loyal to https://www.acwholesalers.com/ having done a handful of purchases from them issue free.



Not my work but these are external line covers - tacky but quickest retrofit:

 

[manwithtools]

Thanks for the tip. I have lots of questions about tying into the existing ductwork. Are you using the ducted mini split for both heating and cooling or just cooling. Is it only used in the master or other rooms too?

We are using the mini split for heating and cooling. It covers the entire master suite including a large bathroom and small utility room with washer and dryer. Our issue was the distance from the main unit to the master suite is over 50 feet of duct going over the top of a vaulted ceiling great room. The flex duct they ran could not deliver enough air and there was no air return on the master side of the house. A really poor duct design for a new house - built in 2023.

 

[danski0224]

Can you elaborate on your fancy ductwork statement the basement?

Correcting the fittings for airflow.

 

[Two Door]

Would it be possible to install dampers which would be used by a zoning system to restrict downstairs flow at night, forcing more to the upstairs?

 

[u3b3rg33k]

I believe that the root cause of poor cooling in my upstairs is that the ducts are too small and they used flexible ducts everywhere but the main supply and return ducts in the basement which are fiber board.

Can you explain how new equipment solved your problem? My heatpump with propane gas furnace backup keeps the downstairs comfortable and the upstairs too in heating season. In the summer the downstairs is comfortable but the upstairs is too hot. I believe that the existing equipment has the capacity, but is constrained by the ductwork. How did you add 11 zones?

Thanks

flex ducts and fiber board are "suboptimal" but that doesn't mean you can't build a system that performs with them. most of that is adequately sizing and installing them.

for example, maybe you need to step up from a 6" metal to an 8" flex to get the same airflow due to increased resistance. but if the air gets there, then you get the cooling.

on a greenfield install, (which is common in new homes around here) with a single stage furnace and AC, they'll do one damper and duct run for upstairs, and one for downstairs.
I didn't have the room or layout for that, so I had the main trunk put back in (the previous owners deleted it and duct-o-pus'd it), and then had takeoffs put in for each duct.
I did 4 zones (upstairs, downstairs, basement, bump-out dining/kitchen), with 11 dampers (one per duct), they're wired up into 4 groups.



the basement zone really serves to NOT heat/cool the basement but still allow air circulation in fan call (vs always going down to open/close a vent).

keeping the upstairs comfortable in the summer is a runtime issue with the system I have, not a system size issue.

once the downstairs satisfied with a single thermostat, the house was the temperature it was. having the fan set to "circulate" on the thermostat helps, but not enough. upstairs was regularly 80F into the wee hours of the morning unless you set it to "ice box" downstairs.

now, the system just keeps cooling the upstairs until the upstairs thermostat hits the setpoint and satisfies. it functions pretty much like any other separate system would.

on the extremely hot days (95+) occasionally the upstairs will get +2F from setpoint, but it comes back down in no time at all.

replacing the equipment was done for a handful of reasons - finishing a partially done remodel in the past left the chimney in the middle of a room, so to get rid of it, the 80% heating appliances had to go, and since they were aging out anyways, well this is GJ, might as well go overkill!


also it's important to note that because my cooling is single stage, each zone must be able to flow enough CFM to keep the system happy, without going over the TESP of the system. that got napkin mathed out, and verified with testing.

my heating is 2 stage with outdoor reset (air temp goes up as the outside temp goes down) - it's incredibly quiet and I can barely tell it's running, vs the roar of the old unit.

 

[PoorUB]

Bathroom A/C is a prime requirement from SWMBO.

Too much hassle for a room you use a few minutes a day, plus if the rest of the space is comfortable, the cool air will migrate into the bathroom. If nothing else, turn on the bathroom exhaust and it will expel the warm air and drag in cool air from the rest of the space.

It sounds to me like you need a four head mini split and cool the bedrooms, or two dual head units, depending on how the house is laid out. Cool the bedrooms, leave the doors open as much as reasonable and the bathroom will be fine. Try mount the heads so they blow out the door ways of the bedrooms if possible to improve circulation.

 

[theoldwizard1]

You can get up to 5 zones…

https://www.garagejournal.com/forum/attachments/img_0987-png.2368816/

You can, but the price goes up quickly ! Also, multi-zone mini-split are less efficient.

 

[AA/FC]

I believe that the root cause of poor cooling in my upstairs is that the ducts are too small and they used flexible ducts everywhere but the main supply and return ducts in the basement which are fiber board.

<snip>

What size are the flex ducts that feed the registers?

 

[u3b3rg33k]

Too much hassle for a room you use a few minutes a day, plus if the rest of the space is comfortable, the cool air will migrate into the bathroom. If nothing else, turn on the bathroom exhaust and it will expel the warm air and drag in cool air from the rest of the space.

It sounds to me like you need a four head mini split and cool the bedrooms, or two dual head units, depending on how the house is laid out. Cool the bedrooms, leave the doors open as much as reasonable and the bathroom will be fine. Try mount the heads so they blow out the door ways of the bedrooms if possible to improve circulation.

if OP goes "minisplit" i'd suggest something like a low static concealed ceiling duct unit:


they're low profile and could be put "inside" if you have enough space to soffit in the ducts. obviously depends on ceiling height etc.
plus you can fit a real filter to them.

 

[u3b3rg33k]

Would it be possible to install dampers which would be used by a zoning system to restrict downstairs flow at night, forcing more to the upstairs?

that's basically what I did. only it's automated.

closing vents can backfire though. if you lose airflow, you generally lose cooling output (or you ice up your coil). you have to remember to re-open them. it often makes noise, too.

OP might consider fan ON at night if not already doing so. that'll help continue to displace the warmer air upstairs. it's not magic but it can make a difference.

 

[Wiz02]

I do like mini splits. if the head can mount through an exterior wall and the line/wire/drain ducting is not too much of an eyesore the way to save money is to get all the physical heads mounted, linesets/wire/condensate line drilled through the wall and seems like two multizone condensers on the slabs or wall mount with power ran. The job would be easier if you rent an articulating lift. A 'cheat pass' around here is the real equipment rental places charge one day for a weekend rental - and also if its a 3 day weekend. I would leave flaring and completing the line set bends at the heads to a paid tradesperson and they can evacuate the lines properly. I am loyal to https://www.acwholesalers.com/ having done a handful of purchases from them issue free.



Not my work but these are external line covers - tacky but quickest retrofit:

I'm getting too old and creaky to DIY a second story install but I still have dreams of doing the minisplit install myself in the garage. There are many options and I want to be as well informed as possible before talking to some contractors.

I'm not sure how SWBO feels about external chases to hide linesets. Good idea to show her your pics.

 

[Wiz02]

What size are the flex ducts that feed the registers?

Sadly 4 inch in most cases

 

[Wiz02]

Would it be possible to install dampers which would be used by a zoning system to restrict downstairs flow at night, forcing more to the upstairs?

Interesting idea and coupled with a tstat in a room we actually use like the master bedroom would allow the upstairs to be comfortable without making the downstairs ridiculously cold.

 

[Wiz02]

flex ducts and fiber board are "suboptimal" but that doesn't mean you can't build a system that performs with them. most of that is adequately sizing and installing them.

for example, maybe you need to step up from a 6" metal to an 8" flex to get the same airflow due to increased resistance. but if the air gets there, then you get the cooling.

on a greenfield install, (which is common in new homes around here) with a single stage furnace and AC, they'll do one damper and duct run for upstairs, and one for downstairs.
I didn't have the room or layout for that, so I had the main trunk put back in (the previous owners deleted it and duct-o-pus'd it), and then had takeoffs put in for each duct.
I did 4 zones (upstairs, downstairs, basement, bump-out dining/kitchen), with 11 dampers (one per duct), they're wired up into 4 groups.



the basement zone really serves to NOT heat/cool the basement but still allow air circulation in fan call (vs always going down to open/close a vent).

keeping the upstairs comfortable in the summer is a runtime issue with the system I have, not a system size issue.

once the downstairs satisfied with a single thermostat, the house was the temperature it was. having the fan set to "circulate" on the thermostat helps, but not enough. upstairs was regularly 80F into the wee hours of the morning unless you set it to "ice box" downstairs.

now, the system just keeps cooling the upstairs until the upstairs thermostat hits the setpoint and satisfies. it functions pretty much like any other separate system would.

on the extremely hot days (95+) occasionally the upstairs will get +2F from setpoint, but it comes back down in no time at all.

replacing the equipment was done for a handful of reasons - finishing a partially done remodel in the past left the chimney in the middle of a room, so to get rid of it, the 80% heating appliances had to go, and since they were aging out anyways, well this is GJ, might as well go overkill!


also it's important to note that because my cooling is single stage, each zone must be able to flow enough CFM to keep the system happy, without going over the TESP of the system. that got napkin mathed out, and verified with testing.

my heating is 2 stage with outdoor reset (air temp goes up as the outside temp goes down) - it's incredibly quiet and I can barely tell it's running, vs the roar of the old unit.

You described my situation exactly, current equipment (single stage AC and heatpump with 2 stage hi efficiency furnace has the the capacity, you just have arctic temps downstairs in order to be comfortable upstairs.

While I don't want to gut the upstairs drywall, all the different options are giving me a lot to think about.

 

[Wiz02]

Too much hassle for a room you use a few minutes a day, plus if the rest of the space is comfortable, the cool air will migrate into the bathroom. If nothing else, turn on the bathroom exhaust and it will expel the warm air and drag in cool air from the rest of the space.

It sounds to me like you need a four head mini split and cool the bedrooms, or two dual head units, depending on how the house is laid out. Cool the bedrooms, leave the doors open as much as reasonable and the bathroom will be fine. Try mount the heads so they blow out the door ways of the bedrooms if possible to improve circulation.

If you spent some time in our bathroom to do business, let alone run a hair dryer after a shower (a hair dryer is not something that I need ) you might change your mind.

Even though the skylight has low e glass, I think that on a sunny day you can fry an egg on the counter. The current duct is positioned on the entry wall to the bathroom and cools the door instead of the room.

However, this whole thread is about getting opinions on different options and whether it's 4 or 5 head, mini splits are definitely an option.

 

[dcg9381]

However, this whole thread is about getting opinions on different options and whether it's 4 or 5 head, mini splits are definitely an option.

When I built a house, I ran this option through a few contractors. It was surprisingly (or maybe not so suprising) expensive, off cuff, $10k or so on a new build for multi-head. Traditional was less expensive.

What I love about it is individual (perhaps) thermostats.

What I hate about it, is these systems are much more "throw away" than traditional HVAC and they're harder for techs to work on.

For this sort of problem, I'm going to talk to a "real" residential HVAC guy that understands flow, what we can do within the bound of existing system - maybe put restrictions on downstairs flow and de-restrict upstairs. There are of course systems that do dual zone, but sometimes take a while to get right.

 

[Wiz02]

that's basically what I did. only it's automated.

closing vents can backfire though. if you lose airflow, you generally lose cooling output (or you ice up your coil). you have to remember to re-open them. it often makes noise, too.

OP might consider fan ON at night if not already doing so. that'll help continue to displace the warmer air upstairs. it's not magic but it can make a difference.

Good point about closing vents. The tstat is in the dining room, which is great for the half dozen times a year we entertain, but is worthless most of the time. I found that closing registers in the dining room has helped regulate temperature in the other rooms downstairs but the upstairs is about 5 degrees warmer than downstairs.

I wonder if a motorized damper that closes downstairs vents at night and an upstairs tstat is a viable option.

 

[Wiz02]

When I built a house, I ran this option through a few contractors. It was surprisingly (or maybe not so suprising) expensive, off cuff, $10k or so on a new build for multi-head. Traditional was less expensive.

What I love about it is individual (perhaps) thermostats.

What I hate about it, is these systems are much more "throw away" than traditional HVAC and they're harder for techs to work on.

For this sort of problem, I'm going to talk to a "real" residential HVAC guy that understands flow, what we can do within the bound of existing system - maybe put restrictions on downstairs flow and de-restrict upstairs. There are of course systems that do dual zone, but sometimes take a while to get right.

Where do I find this real residential HVAC guy?

 

[dcg9381]

Where do I find this real residential HVAC guy?

I can't tell you in your neighborhood... The "residential" guy I used only does "new builds". And he's got a ton of business... Well, he did, until interest rates hit 7%.

I think the idea of retro-fitting 4+ ductless heads into an existing structure may ellipse the cost of putting restrictors downstairs and pumping more air upstairs, but I'm guessing as an engineer who knows nothing about HVAC, other than how hard it is to install single head ductless systems.

 

[Two Door]

Where do I find this real residential HVAC guy?

Look for the guy that talks technical on his website - like "air quality", "manual J", "blower door test", "air sealing", etc. You don't want the company with ten trucks, also does plumbing and electrical, flashy website, offers financing, etc.