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Armstrong 80 Issues


I have been having problems with my furnace since we bought our home (2 story 105 years old) in Michigan.

We purchased the home in 2006 and found out the furnace was installed "Brand New" in 2005. While it may in fact be new, it certainly does not heat very well. (ie. Luke-warm air).

I called a furnace expert to obtain a free quote. While here he said that the burners looked fine, recommended changing the blower to high speed rather than Med/High where it was.

He also said we were restricting airflow due to having a couple of returns disconnected. I explained that with the original returns and nothing removed, the heat was no better than it was now.

He provided me with a quote and went on his way.

Wood floors
Blown in insulation (2005)
Michigan basement (dirt floor) nightmare for filters
Main Room - 4 Windows 6'tall X 2' wide. We would like to remove 2 of the windows at some point. Many projects on the list though, and now unemployed as well.

Main Room Length - 11W X 21L X8H (technically 9' ceilings, but drop ceiling in place at 7'8").

3 - Exterior Walls
1- Window facing east
2- Windows facing South
1- Window Facing West

Dining Room - 6'tall x 2' wide
2 - Exterior Walls
1- Window Facing East
1- Window Facing North
1- Door

Kitchen - 30"tall X 36" wide
1- Exterior Wall
1- Window Facing east

Bath - 36" wide x 2' tall
1 - Exterior Wall
1- Window facing east

Laundry - 6' wide x 3' tall
2 - Exterior Walls
1- Window facing east

white Rodgers Thermostat - Gas / Elec (no other settings). Can be set to slow cycle or fast cycle. No change to amount of heat when changed. Currently on fast.
Setting: has always been 68-69*.

Armstrong Ultra V Tech 80 Upflow 75K BTU Gas Furnace
Motor - 1/3 HP
Speed - High (was running on Med/High)
Max CFM - 1271
Original Returns - 3
1 - 12 X 12 in main room
1 - around corner next to stairs
1 - in back of home near laundry room / bath room
Current Returns - 1 12 X 12 in main room
Current Supplies (Up) - 4

Original Supplies (Down) - 7
Current Supplies (Down) - 6
4 - Main living space (now 3)
1 - Kitchen
1 - Dining Room
1 - Bath

The original supply that was disconected downstairs was 5-6 feet from the 12 X 12 return and it appeared that this would be drawing heat right back into return, rather than heating the room.

The other returns that was disconnected (1 in walkway in laundry room, 5 feet from the only supply in that room). The bathroom is next to laundry room and has 1 supply.

The remaining return that was disconnected is 6 feet from 12 X 12 return, around the corner next to stairs.

The main reason the returns were disconnected was based on a paper being held over them. You could not tell there was any significant draw.

We knew the previous home owner and had been in the home both during summer months and winter months. The home was never appropriately cooled, nor did it heat well. After buying the home and consulting with people that said they knew a little about HVAC we have changed the original ductwork that was in place.

The original AC has been disconnected as it was simply a mess of ductwork. Unbelieveable actually. This was connected to a monstrosity of ductwork that was original, also removed.

I was hoping to gain better heating after removing the original supplies and returns, replacing supply lines in basement with 6" round.

The furnace did not work well (very little heat from supplies) when everything was original...and it still does not heat well to be honest. The air coming out was and is luke-warm. I suppose there is no answer other than it being an 80% EFF. model.

Should I change the fan speed from High down to Med-Low or Low?

Initially it was on Med-High and never seems to provide enough heat. If I were to change the fan speed to Low, how can I be certain to avoid the
cut-off switch temperature?

Nothing in the manaul concerning this, or any other speed adjustment.
Lastly, I found a BTU calculator (per room, accounting for windows doors, etc.) and used that to determine what our requirements are.

Total calculated / required BTU for our 1,046 Sq. foot home is 39,843. Is 75,000 BTU to much, or is something else the root cause?

The basement area was not figured into calculation. It is roughly 21 X 21, if that and there is no supply nor has there ever been.

No insulation around any exposed ductwork.

Since what I have now is obviously incorrect, I would really appreciate some direction. I currently have a total of 4 6" round coming directly from the plenum. At the rear of the plenum there is a square supply line that has 2 8" original supplies coming off of it. 1 feeds the laundry room, 1 feeds the bath room.

There is no other supply trunk currently. The 3 supply lines that feed the main 12 X 21 room are 6" round and go directly into the plenum. What size do I need to have the supply trunk (to living room) for starters...if I even need one?

So it looks as though the ductwork is undersized as well.

Thanks in advance.

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