2-story HVAC Issues

[NinjaSalad]

We live in a 2 story home built in 1925. Central heat (natural gas) and AC were added to the home at some point - and it appears as though it was installed on the first floor many years prior to the second floor.

All of the duct work for the first floor (sheet metal) is in the basement and I noticed that when the AC is on, it is entirely too cold in the basement. A little poking around revealed many many air leaks in the duct joints so I spent most of the past weekend using aluminum duct tape to seal every single joint I could reach. I also found a lot of leaks around the vents/registers that I am in the process of sealing up as well.

I'm not an HVAC expert by any means but the second floor installation baffles me. Basically, a giant chase was built through the middle of the house that extends from the basement into the attic. One huge flex duct goes through the chase and then splits into 4 separate ducts to provide air to rooms on the second floor. It seems to be a fairly inefficient attempt at cooling the upstairs as there is very little air flow through these vents and it is sweltering hot upstairs in the summer - we are using window AC units at night to cool our bedroom and our sons bedroom.

We would like to eventually install a separate unit for the upstairs, but that's not in the budget at the moment so we are looking for little things we can do to improve the situation.

There are no returns on the second floor, but there are 3 small ones on the first floor. Could this be a contributing factor to our problem? It's probably not something we can fix at the moment but would need to consider when the time comes for the second unit.

I haven't yet checked for leaks in the attic, but it does look like we could use a bit more insulation up there.

Would there be any benefit to wrapping the sheet metal ducts in the basement with insulation? Is the bubble wrap type effective?

Anything else I haven't thought of yet?

[Milspecstache]

Have you looked at ductless?  I have it in my house as the only heating and cooling method and one unit upstairs can cool the entire house and in the winter, one unit downstairs can heat the entire house.

To run it you would need:
240v at outside pad (for my model)
run wiring up side of house as well as pex drainage line for condensate
hang the interior unit on an exterior wall, preferably to rear to hide wiring and drain line

Very efficient and easy to replace.  No more moldy ducts.  Doesn't look the best but we love the quietness and efficiency.

[sokoloff]

The poor ducting upstairs seems to be the root of your problem. Yes, you can seal the ducts in the basement (as you are) and can insulate them, but the root of the problem is that the poor ducting is causing the system to run too long, and the only place the excess cooling can go is into the basement. With proper returns from the second floor, your basement overcooling problem would go way down or away. IOW, stop hacking away at those leaves and work on the root.

If you can't improve the duct situation upstairs (meaning provide high volume returns), then you should definitely look at a mini-split like @Milspecstache suggests. (Even if you can do it, the expense and hassle of doing it might push you towards the ductless mini-splits.)

I'm pretty hardcore DIY, and I'd consider DIYing it, but the install is generally easy and not particularly time-consuming for an HVAC contractor to do (so might be cheap enough). The minisplit will be more efficient than the window rattlers, though probably equally ugly inside.

[Papa bear]

In general, you need the same size returns as the the amount of air supply going up.   So if you have 3 6" round ducts, you need 3 6" round ducts return (or the equivalent size of air, so a big 10x8 rectangle, or 2 3.5"x 13.5"). In theory, you want your supply to terminate on the exterior of the building (normally under a window) and the returns high up on the wall near the ceiling in the center of the home with equal supply and return in each room.  Optimally, you will have no ducting run along an exterior wall.

This may be very difficult for you to achieve. So, one big return in the hallway is ok, but you have to make sure you have an inch gap of space under each door to allow for air flow. 

For returns now, they want you to hard pipe the entire run, where previously you could use an open chase between studs and drywall to act as your return.  This may be easier for you to achieve especially if your home was balloon framed and does not have fire blocking.

Also, flex ducting doesn't allow for the same airflow as smooth pipe 


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[Fishindude]

I'm not an HVAC expert by any means but the second floor installation baffles me. Basically, a giant chase was built through the middle of the house that extends from the basement into the attic. One huge flex duct goes through the chase and then splits into 4 separate ducts to provide air to rooms on the second floor. It seems to be a fairly inefficient attempt at cooling the upstairs as there is very little air flow through these vents and it is sweltering hot upstairs in the summer - we are using window AC units at night to cool our bedroom and our sons bedroom.

We would like to eventually install a separate unit for the upstairs, but that's not in the budget at the moment so we are looking for little things we can do to improve the situation.

There are no returns on the second floor, but there are 3 small ones on the first floor. Could this be a contributing factor to our problem? It's probably not something we can fix at the moment but would need to consider when the time comes for the second unit.

I haven't yet checked for leaks in the attic, but it does look like we could use a bit more insulation up there.

Would there be any benefit to wrapping the sheet metal ducts in the basement with insulation? Is the bubble wrap type effective?

Anything else I haven't thought of yet?

Your gut instinct is likely correct.  Sounds like a pretty crummy installation from day one.  Flex duct gets used a lot because it is cheap and easy, but the air flow is terrible compared to smooth sheet metal.   I like to limit flex duct runs to no more than the final 6' to the diffuser outlet.

Fixing any leaks in the duct was a good move, and for now running some window units is probably your best solution.   Old homes were not built with AC systems, so there is often not any good places to run ductwork to a second floor.  I'd call in a trusted HVAC professional and have him look over what you have and offer suggestions.  Sounds to me like you are in need of pretty much a complete new system and possibly a second system for upstairs.

[CareCPA]

If you find room in the budget, I would think about something like this:
https://www.alpinehomeair.com/viewproduct.cfm?productID=453074777

It sounds like you have attic access (maybe I'm misreading) - this is essentially the ductless that you see on walls, but it mounts into the ceiling and looks much better (in my opinion).
Of course, this is not a recommendation on sizing or number of zones since I don't know the layout of your house.