[Bklotz]

We bought as 2003 built two story in MN 1.5 yrs ago. It had the original undersized furnace and ac. The winter was cold and the summer hot. We bought/had installed a new furnace and ac (3 ton). So far this summer our top floor is even warmer than last year. Thermostat on the main floor set to, and holding, 73. The top level with all the bedrooms will be 83. I can feel a little air coming out upstairs but not enough to cool. The backside of the house faces west with no tree cover. We have, I believe, 2 feet of blown insulation in the attic and snow doesnt melt off the roof in winter. So I dont believe its lack of insulation.

Any recommendations to get more air moving in the top level?

Thanks

 

[Bud9051]

Hi Bk and welcome to the forum. Do those upstairs rooms each have a return for your system? How many returns and where are they?

Bud

 

[SPS-1]

Your thermostat should have a switch or setting - FAN AUTO or FAN ON.
Have you tried running the fan furnace fan continuously ? That should better distribute the air.
Possibly close the dampers a little on the main floor registers.

 

[pumpkin11]

Get your ducts professionally cleaned,

You would be surprised at how much more effective and efficient your heat and A/C are with clean ducts

 

[roughneck]

What size was your old unit prior to the new 3 ton system?
What duct modifications were made to accommodate the larger unit?
What was used to determine the old unit was too small?
Your original issue was likely duct related, not unit capacity. Now with a system that may be oversized for the load, your short cycling and have further decreased the second floors delivered cooling capacity.

 

[SPS-1]

Get your ducts professionally cleaned,
You would be surprised at how much more effective and efficient your heat and A/C are with clean ducts

Oh please.

Are you the guy who calls me twice a week trying to sell me Air Duct Cleaning ?

 

[pumpkin11]

Oh please.

Are you the guy who calls me twice a week trying to sell me Air Duct Cleaning ?

I'm just speaking by personal experience, I had the same problem, getting my ducts cleaned instantly corrected the problem, night and day difference, no need for petty comments

 

[diyorpay]

SPS is likely correct about your issue.
Your new higher efficiency unit may not be efficient because of fast cycling. (Thermostat on main floor says 'shut down, desired temp reached'.)
I would close downstairs registers to almost fully closed and see if upstairs cools better. Then gradually open downstairs registers in small increments.
Once accomplished, consider changing AC fan speed from HI to next lower setting. That will cause unit to stay on longer to satisfy thermostat and provide higher efficiency, better comfort, more humidity removal. Heavier drapes upstairs might work. Don't close bedroom doors at night. Use the cheap filters but change every month.

 

[beenthere]

If the old unit was 2 tons. And you increased to 3 tons. You increased the air flow requirement by 50%. Did you have larger duct work installed to move the extra amount of air the new equipment needs to move?

 

[argile_tile]

from when your AC turns on until it turns off the whole volum of air (WxLxH) of all rooms should be circulated by the central fan

it only does this if you have your room's vents set properly

top causes of bad airflow: vents closed, return blocked, after-market/after-build basement taps into the air ducts, WARPED IMPELLER. cleaning your vents: likely not your problem.

if your furnace wobbles even a little the ENERGY LOSS on the fan is way more than you think: like 50% of all your fan is going into wobbling the furnace

CAUSES OF WOBBLE / RATTLE of furnace box:

1) warped or ding'ed impeller fan blade

2) fan not firmly seated or screwed, or screwed into cheap sheet metal (put a brick under that bad boy, see if it starts up smoother, runs smoother: and air starts flowing 2x as fast, meaning - the fan housing resting on a brick wedged under it so it can't "bob" up and down easily, is firmly seated can't move around)

 

[argile_tile]

so obviously if you close all vents in basement (assuming those are after-market add-ons, but some air is needed to prevent musty smells), partly close vents on main floor, then 2nd floor up should blow fine

but that may not be your problem - your reduced air flow is likely from fan wobble assuming you already did the simple vent thing, nothing else

I DID FORGET ONE THING. If your fan capacitor is failing it will cause the fan to "have hard starts, perhaps stop running before it should". sometimes bad caps (depending on how they fail) could cause poor performance before causing the more noticeable symptoms of "early stops and hard starts".

so if your furnace doesn't wobble or "vibrate" at all, seems smooth to tactile touch, then perhaps you have bad capacitors

very rare would be a motor which had good caps but not spinning at the target RPM, they don't usually fail that way if they ever fail at all

 

[argile_tile]

I forgot to mention. ALL YOUR DOORS NEED TO BE AJAR for the upstairs to be cooled. The air must flow to the return vent un-restricted or you won't get cooling upstairs. This sometimes confuse people who like to keep bedroom doors closed for privacy. A mitigation is to install a vent (above) the door. The door opening or vent must the the same size as the supply vent in the room. It must be done for every room not just 1.