Just wanted to bump this back to the front page. Anyone have an opinion on the contractor's idea of adjusting the dampers and trying an inline fan?

(If I need to add any info or pictures I'm happy to do it.)

 

I have a job next week where I'll be removing an inline fan because it did not improve air flow.

Your house has a duct deficiency, not a blower deficiency. Those ducts were designed to deliver heat to the second floor and very little air flow was needed. You'll never get as much air as you need for cooling to the second floor through those small ducts.
A small cooling system (of the proper size) in the attic with ceiling registers will make the second floor comfortable.

 

Thanks for the reply, kdean1.

I've started to think of the second cooling system in the attic as a last resort -- too many concerns about efficiency. Do you think I could fix this problem with better sealing / insulating in the attic AND by running two or three more 4x12 ducts to the upstairs? I have two, maybe three stud cavities in the walls where it would work nicely. I'm not sure if I should do all supplies, a supply and a return (there are no returns upstairs), or what.

But maybe even adding three of those would still leave me woefully under-ducted. I'll be curious to see what you and others think. Thanks for your time, though.

If anyone else has any experience with inline fans, good or bad, please chime in.

And if anyone knows how much is too much when it comes to damper balancing I'd love to hear it.

 

Part of the issue is that your house needs MORE air flow upstairs to cool what is a warmer level than the downstairs. I doubt you'll get enough volume with a few more 4x12 ducts.

A separate system upstairs will provide much better control for each level as well as the comfort you're hoping to achieve.

Tightening the house in never a bad idea but it won't change it to the extent that your current duct system will be adequate.

As for damper balancing, use caution. Closing too many dampers will increase the pressure on the duct system to the point that the blower can't move enough air for the air conditioner to properly cool.

 

That makes sense about the airflow. Thank you for your advice.

On the dampers, I've played around a little myself. There are five supplies downstairs and I left two completely open and half closed the other three. (I didn't fully close any of them.) Is that too aggressive?

 

If I understand your sketch, I see 8 ducts total for the house. Two are closed and three half closed.
Based on my experience, most houses have undersized duct systems and oversized equipment. The effect of closing too many dampers is a reduction in total air volume with an accompanying reduction in cooling. A tipping point will be reached which will cause the indoor coil to frost, then freeze and stop all air flow. A dirty air filter or a 1" pleated filter (even when clean) reduces air flow still further and makes it all worse.
I don't mean to be all doom and gloom but I think closing dampers may be inadvisable. Of course if all the ducts are 10" diameter or larger they might be okay. But that is seldom the case.

 

Please don't apologize. I've read about the coils freezing -- hence my nervousness about this contractor's proposal to balance them.

There are eight supply runs in the house. The three upstairs I left open. Of the five downstairs, I left two open and half-closed three. But it sounds like even that may be impeding air flow too much? I'll go back to opening them all if that's the case.

Just a standard one inch filter -- I change it pretty frequently.

 

Sounds like your duct system is already too small. If that's the case Closing off dampers will only make the unit have less capacity overall.

I would agree that a seperate system for the upstairs and duct modifications downstairs or complete reduct with zoning and giving up a little space to get adequate ductwork upstairs is what it'll take to make it right.

My experience with inline fans is that they actually reduce airflow by causing restriction in the duct and they are noisy.

 

OK -- no more messing with the dampers and no inline fan. Thank you both for your advice.

 

You can't beat science. Hot air rises, cold air falls. With a forced air system you are basically removing air from the space, adding or removing heat, and then returning it to the space. In a single story home this is done by even the simplest of systems and usually performs ok. In your case you have a second floor. You're trying to "push" cold air UP to that second floor. You are not returning any of the heated air from that second floor back to the equipment to be cooled. Until you get a decent sized return on the second floor (suggest ceiling) the problem is going to persist with you existing system. The amount of comfort all depends on whether or not what you have now is actually sized to handle the entire home.

As someone else stated, in older homes the only concern was getting heat to the second floor which was in most cases bedrooms that most people like a little cooler anyhow. The installers relied on the fact cold air falls to get the air back to the furnace via stairs etc. to be reheated and returned to the living spaces.

You've already said that you have stud spaces you can get more ductwork to the second floor. I would suggest that you use that space, and maybe a little more to get at least one good sized return up there.

I've worked on a lot of old 2 story farm houses that originally were heated by very large gravity furnaces. If we were luck we were the ones upgrading them to high efficient equipment that usually meant the large chimney going from the basement through the attic was going to be abandon. We pulled many a large flexible liner through these exiting either in the attic and then ducting them to the ceiling upstairs or into a central hallway. We capped the top off and stuffed the top with insulation down to the liner. Was it a perfect solution, usually not "perfect", but it got the owners a good amount of comfort which could later be upgraded if they ever did extensive remodeling inside the home.

 

Thanks, firecontrol. I've thought about using our chimney, which has two 8" flues. One is currently used by the gas hot water heater; the other I'm saving for a wood-burning insert in the fireplace downstairs. But I could always give up on the insert, upgrade the water heater to a high efficiency, and use the chimney to run more ductwork. We'll have to see.

In the meantime, let's say I can run two 12x4 ducts to the upstairs. Both returns or one supply and one return?

Let's say I can run three. Two returns and one supply?

In the blueprint in my original post I marked the potential locations for returns in yellow. I'm thinking the ones at the east and west end of the hallway would make good wall returns, mounted up high. I'm thinking the one in the middle would make a good floor supply. But it's all flexible.

Again, thank you all for your advice.