HVAC Quandry

[woods]

Currently sleep on the first floor, but in the process of moving the bedrooms upstairs. Scratching my head on what to do about the cooling. Just spent our first night upstairs and it has to be 10 or 15 degrees warmer up there at least. We have 2T central air unit and it keeps the downstairs cool just fine, but upstairs is still hot.

There are two (I think) issues with the current system.

First, there are four 8" vents leading from the basement to the attic, that then feeds the two rooms. And one of those 8" vents splits into a T in the attic. We have dampers in the basement and I shut the one off leading to the upstairs bathroom. So ultimately there are three 8" vents, followed by a T in the attic. I'm thinking this is far too much ducting. By the time it reaches the attic, it barely eeks out. I was planning on removing the four 8" ducts and replace with just one duct. In the attic, run a hard duct (not the flex stuff I have now) the entire length with tapered ends. Then tie the single duct from the basement to the attic duct. Should give me more thrust from the furnace. Having four ducts, then splitting into five I think is spreading it too thin.

Second is we have three returns on the first floor, but not a single one on the second. Something tells me I need a return upstairs. We had the doors open last night to the downstairs though, but not sure if that does the same thing as a return.

I'm almost at the point of closing the dampers to the upstairs, leave them all open downstairs, and run a window fan in the upstairs bedroom pulling the air out to draw in the cooler air from downstairs.

Thoughts or suggestions?

 

[Lawless]

I have the same problem in the house we just bought. I haven't bothered tracing the ducting but have made an improvement none the less. I closed off half of the registers on the main floor and it increased the air flow on the second floor. I have given some thought to the return air but am going to leave it alone for a few days and see what happens.

I am working with the principal that hot air rises cool air falls so with that being said I've kept the second floor windows shut during the heat of the day.

One thing that just crossed my mind is perhaps installing booster fans to provide more flow to the second floor.

I might just head off to youtube and see if there is anything there for pointers.

 

[woods]

I have the same problem in the house we just bought. I haven't bothered tracing the ducting but have made an improvement none the less. I closed off half of the registers on the main floor and it increased the air flow on the second floor. I have given some thought to the return air but am going to leave it alone for a few days and see what happens.

I am working with the principal that hot air rises cool air falls so with that being said I've kept the second floor windows shut during the heat of the day.

One thing that just crossed my mind is perhaps installing booster fans to provide more flow to the second floor.

I might just head off to youtube and see if there is anything there for pointers.

See, I was thinking that the hot air needed a place to escape out of. It just kind of dams up on the 2nd floor and has nowhere to go.

I dug a little bit on this over the winter time, and it seems the final conclusion on the booster fans was that they are somewhat of a gimmick.

 

[scooter2374]

If it is anything like my moms old 3 level condo, you would be doing yourself a favor by adding a second unit dedicated to the top floor.

 

[Bowe]

Lots of options to choose from, if possible adding high wall returns upstairs should make a big difference. The hot air is stratified up there with nowhere to go. Throttling the dampers for downstairs to achieve a better balance could also help.

We've done alot of work trying to get one system to cool multiple levels, but if the house and HVAC system wasn't built with that in mind the gains are minimal compared to the effort. The go to seems to be adding a single or multi head mini-split to the second floor, every customer I've talked to afterwards is thrilled with the comfort they now have.

 

[Mac5005]

Add return upstairs, throttle the downstairs dampers maximize upstairs comfort,

or

ductless mini split upstairs.

 

[Ted_Kaczynski]

Or
burn house down
Collect insurance
Party your ass off like it's 1999


I vote move a return upstairs and throttle the feeds down stairs. Also make sure your attic is well insulated and vented, and if any ducting is in it make sure it is fucking coated in insulation.

 

[woods]

Yea, we have all the dampers closed downstairs.

We do have a window a/c I can put in the window upstairs, but we have central air so I sort of wanted to leave that as a final option.

But yea, I'm thinking the lack of returns upstairs isn't letting the hot air escape anywhere.

 

[rugger]

Yea, we have all the dampers closed downstairs.

We do have a window a/c I can put in the window upstairs, but we have central air so I sort of wanted to leave that as a final option.

But yea, I'm thinking the lack of returns upstairs isn't letting the hot air escape anywhere.

It’s not about air “escaping”. It’s about having a delta (difference) in pressure. You are attempting to pump higher pressure air in the space. It’s like watching the weather. Weather always flows from an area of high pressure to low. The air return is your low pressure. You need it for the air to move.

 

[woods]

It’s not about air “escaping”. It’s about having a delta (difference) in pressure. You are attempting to pump higher pressure air in the space. It’s like watching the weather. Weather always flows from an area of high pressure to low. The air return is your low pressure. You need it for the air to move.

I gotcha.

I'll have to see how bad it is to install a couple returns upstairs. We have three downstairs. Be nice if they align somewhere upstairs that I can install one. Dad's a master carpenter, so next time he's over we'll see what we can do. Think installing returns is going to be the biggest improvement.

 

[MurderYota]

Install a mini split upstairs. Everything else is a waste of time. 2 tons is most likely too small anyway

 

[woods]

We slept upstairs last night. Placed a beefy fan at the top of the stairs to push the stagnant air downstairs. Huge difference. It was still cooler downstairs, but it was nicer. We'll stick with that for now, and when things get back to "normal", I think I'm going to grab a few doorframe fans to help circulate the air out of the rooms and into the downstairs. Start there and see what happens.

 

[scooter2374]

Glad you got some relief, I fucking hate sleeping in a warm or hot room.

 

[IEATRKS84]

how about closing all the vents in the basement and most in the first floor while opening the ones upstairs???

Wild theory i know, but it might just work :/

 

[NOTHINGWILLCHANGELANCE]

put a multi head mini split system into every bedroom. way way better life comfort that way. you can get cassettes for in ceiling units and send the linesets out via the attic.

short of that its all about return air. you need to get bigger/more returns in the bedrooms.

 

[Tmackcj5]

I'm in a similar boat.

We bought a 2 story 1 AC house last year. My kid's rooms are on the 2nd level. I expected it to be warmer up there, but it seems like the upstairs has very poor air flow. One of the rooms seems like it has almost no air coming out of the register. The strange part is that the AC unit is in the attic and the closest room is the warmest room. There are several returns on the second floor. I haven't been able to figure out why the cool air flow is so bad to a couple of the rooms. I need to look better to see if there are some inline dampers or something choking air to those rooms.

 

[woods]

how about closing all the vents in the basement and most in the first floor while opening the ones upstairs???

Wild theory i know, but it might just work :/

We have dampers in the basement that I can control to the 2nd floor. I leave three of the open since one is for the upstairs bathroom. We also close all the floor vents on the 2st floor. It helps, but the air coming out of the ceiling vents jest barely eeks in.

short of that its all about return air. you need to get bigger/more returns in the bedrooms.

This is the problem we've run into. Getting the hot air out of the upstairs. We'll try the door frame fans for now since the big honkin' fan at the top of the stairs did a good job. Want to try some of the simpler options before I start cracking holes into walls and floors building returns.

 

[NOTHINGWILLCHANGELANCE]

We have dampers in the basement that I can control to the 2nd floor. I leave three of the open since one is for the upstairs bathroom. We also close all the floor vents on the 2st floor. It helps, but the air coming out of the ceiling vents jest barely eeks in.



This is the problem we've run into. Getting the hot air out of the upstairs. We'll try the door frame fans for now since the big honkin' fan at the top of the stairs did a good job. Want to try some of the simpler options before I start cracking holes into walls and floors building returns.

do the bedrooms have returns in them? thats critical. it stinks having to get it back if they dont have it. might be cheaper to go to a multi head miniplit.

 

[woods]

do the bedrooms have returns in them? thats critical. it stinks having to get it back if they dont have it. might be cheaper to go to a multi head miniplit.

No returns upstairs.

I hear yea on the minisplits, but if he had the returns the current central air unit should be sufficient. Kind of sucks having to have two separate a/c units. I'd want to connect to the returns somehow if I could.

 

[NOTHINGWILLCHANGELANCE]

No returns upstairs.

I hear yea on the minisplits, but if he had the returns the current central air unit should be sufficient. Kind of sucks having to have two separate a/c units. I'd want to connect to the returns somehow if I could.

no return is 100% the issue. he might be able to do a main trunk back to the air handler.

I personally like 2 units. one for main area, one for bedrooms. then each bedroom can set to their comfort without freezing out the main floor space. In my house we pick the main floor up to 76 at night while the bedrooms are 68.

 

[woods]

I personally like 2 units. one for main area, one for bedrooms. then each bedroom can set to their comfort without freezing out the main floor space. In my house we pick the main floor up to 76 at night while the bedrooms are 68.

That's a fair point too. hm.

Everything is at a standstill for the moment until we figure out what is happening with wife's employer. If I can get out of this with a few fans I'd rather do that for now. But yea, setting the two temps would be a nice feature.

 

[NOTHINGWILLCHANGELANCE]

That's a fair point too. hm.

Everything is at a standstill for the moment until we figure out what is happening with wife's employer. If I can get out of this with a few fans I'd rather do that for now. But yea, setting the two temps would be a nice feature.

if you're all about being cheap then its not the way to go. if you're about life comfort then my god, its worth every penny.

I hear ya on waiting and seeing. a basic 3 room, 9000 btu per room setup is right around 2-2,500 in unit cost. dont forget any electrical work it takes to get there. older homes with 100a service may need a big boy panel to make it work.

 

[NOTHINGWILLCHANGELANCE]

also hope your wife's employer does the right thing for you guys.

 

[SomeGuy]

No returns? How do you expect any air flow upstairs? Needs returns.

Once that's done, run the blower on the furnace to circulate the air through the house continually so you don't have heat build up. We have a DC variable speed blower in our furnace, so leave it on low in the summer...uses hardly any energy but keeps the temperature even throughout the house, we're within 1-2 degrees between all the floors (basement, main, upstairs).

No need whatsoever for a mini split to get an upstairs cool.

 

[Roc Doc]

It’s not about air “escaping”. It’s about having a delta (difference) in pressure. You are attempting to pump higher pressure air in the space. It’s like watching the weather. Weather always flows from an area of high pressure to low. The air return is your low pressure. You need it for the air to move.

I got into an argument with a medic about that a couple years ago. Technically air "falls" into the lungs, it's not sucked in, when your lungs expand it creates a lower pressure zone and ambient air pressure rushes in to the low pressure. He wouldn't back down so I let it go.

 

[woods]

No returns? How do you expect any air flow upstairs? Needs returns.

Once that's done, run the blower on the furnace to circulate the air through the house continually so you don't have heat build up. We have a DC variable speed blower in our furnace, so leave it on low in the summer...uses hardly any energy but keeps the temperature even throughout the house, we're within 1-2 degrees between all the floors (basement, main, upstairs).

No need whatsoever for a mini split to get an upstairs cool.

Ehhhh, I moved in here like this. The place has a few things that are questionable. I honestly think the second floor was an afterthought. The entire garage is wire with 14G that I have to tear out and redo. My compressor throws the breaker if I have any lights on. That sort of thing.

I know the returns are the big issue here. Just need to figure something out. May end up calling a HVAC guy to see if they could somehow connect the upstairs to the downstairs.

 

[SomeGuy]

Ehhhh, I moved in here like this. The place has a few things that are questionable. I honestly think the second floor was an afterthought. The entire garage is wire with 14G that I have to tear out and redo. My compressor throws the breaker if I have any lights on. That sort of thing.

I know the returns are the big issue here. Just need to figure something out. May end up calling a HVAC guy to see if they could somehow connect the upstairs to the downstairs.

What's wrong with 14/2 wire? It's the rated size for 15 amp circuits. Most of my garage is wired with 14/2 for lights and the regular outlets.

Your compressor should just have a dedicated circuit, they will pull a full 15 amps on their own, especially at startup and with a couple hundred watt light bulbs it's no wonder it trips.

 

[woods]

What's wrong with 14/2 wire? It's the rated size for 15 amp circuits. Most of my garage is wired with 14/2 for lights and the regular outlets.

Your compressor should just have a dedicated circuit, they will pull a full 15 amps on their own, especially at startup and with a couple hundred watt light bulbs it's no wonder it trips.

Entire garage is wired into one circuit. What's the recommended gauge? I thought it was 12/2? Its a gauge up from the recommended rating.

 

[Chevy_man]

Entire garage is wired into one circuit. What's the recommended gauge? I thought it was 12/2? Its a gauge up from the recommended rating.

You need 12/2 to the compressor. Dedicated circuit. 14/2 is fine for lights and receps.




Get a pro to come out and design the ideal system for you. There is a great amount of magic in duct sizing the average "installer" doesn't know dick about.

Lack of airflow is almost always duct sized too small. You don't want velocity with the low pressure furnace fan, you need volume. Small duct increases velocity for a short run, but overworks the fan and the air can't move through the duct while it's still cool.

 

[Ransil]

You need 12/2 to the compressor. Dedicated circuit. 14/2 is fine for lights and receps.




Get a pro to come out and design the ideal system for you. There is a great amount of magic in duct sizing the average "installer" doesn't know dick about.

Lack of airflow is almost always duct sized too small. You don't want velocity with the low pressure furnace fan, you need volume. Small duct increases velocity for a short run, but overworks the fan and the air can't move through the duct while it's still cool.

Seem the pro is the reason there is an issue