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Old 01-23-2009, 06:47 PM   #1
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Greetings,

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.

Home:
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
1-Door

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
1-Door

Specs:
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*.

Furnace:
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.

Reasoning:
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.


*Edit - 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.

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?

I also found this:
8 inch is about 300 cfm good for about 2000 cu ft of room.
7 inch is about 210 cfm good for about 1200 cu ft of room.
6 inch is about 140 cfm good for about 800 cu ft of room.

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

Thanks in advance.


Last edited by Tech08; 01-23-2009 at 08:55 PM.
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Old 01-24-2009, 06:46 AM   #2
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those returns sound like they are useless,how is the return right at the filter section is it negative bigtime at any speed.heating is always lo speed because you want to have the slowest air across the heat exchanger so the air can pick the temperature and send it up.the reutrn duct should rise out of the basement with a maximum of 2 grilled taps to pull each floor..........might be toooo free.unless somebody else kicks in here i would say the fan should be low always in the heating modes hi/lo heating call,and always hi for cooling.the main supply and reutrn should be as tight with the connections as possible...especially that supply trunk.cut down on those returns if it is more then 2 and get back on that filter negative on the side of the unit.have you ever froze up in cooling season or tripped hi limit with the heating?how is the flame on that burner hi and or lo running.

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Old 01-24-2009, 07:00 AM   #3
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Well, your CFM for the 8,6, and 7" you listed is a wives tale.
And if you put that much air through them, you have loud supplies.

Either your furnace is not getting enough gas supply. And not burning at rated capacity.
Or, your return duct leaks too much.

Check your return duct for leaks.
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Old 01-24-2009, 10:30 AM   #4
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Quote:
Originally Posted by biggles View Post
those returns sound like they are useless,how is the return right at the filter section is it negative bigtime at any speed.heating is always lo speed because you want to have the slowest air across the heat exchanger so the air can pick the temperature and send it up.the reutrn duct should rise out of the basement with a maximum of 2 grilled taps to pull each floor..........might be toooo free.unless somebody else kicks in here i would say the fan should be low always in the heating modes hi/lo heating call,and always hi for cooling.the main supply and reutrn should be as tight with the connections as possible...especially that supply trunk.cut down on those returns if it is more then 2 and get back on that filter negative on the side of the unit.have you ever froze up in cooling season or tripped hi limit with the heating?how is the flame on that burner hi and or lo running.
Thanks for the reply biggles. As I mentioned in the original post, I don't have an existing trunk. The current supply lines come directly out of the plenum. That was also a question. If I need to make a new supply trunk, how big does it need to be?

Never froze up with A/C as it was such a mess of gigantic ductwork the airflow during cooling season was less than during heating, so all A/C mess has been removed.

The return duct:
The only return that is currently connected is a 12 x 12 grille with a large duct going straight into the return drop. I have no return trunk either, only the drop. Unfortunately I have no photos of the original trunk lines to offer. Also, if i need to make a new return trunk, how big should this be?

I have not tried placing the fan speed on low. Originally it was on Med/Hi and then changed to high. If I change it to low speed, how will I know if the safety cutoff gets tripped, and how is it reset?

Thanks again.
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Old 01-24-2009, 10:39 AM   #5
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Quote:
Originally Posted by beenthere View Post
Well, your CFM for the 8,6, and 7" you listed is a wives tale.
And if you put that much air through them, you have loud supplies.

Either your furnace is not getting enough gas supply. And not burning at rated capacity.
Or, your return duct leaks too much.

Check your return duct for leaks.
Thanks for the reply BeenThere. I was poing around the forums and can't be sure, but I thought I saw the reference to the pipes on this site. I have made updated notes refelcting your response. I appreciate it, I have been chasing myths on HVAC for far to long and really need to get the truth on matters to get things resolved.

How can I check the gas supply and or burn capacity? Since I am an obvious newb in HVAC, I have no special tools or money to purchase them due to joining the unemployed ranks recently. The HVAC expert that I recently had here stated that my flames looked fine, but he did not go further.

As far as the return leaking I am certain there are no leaks. The pipe (at least 12" perhaps 14" around) leading to the drop is sealed quite well. Also tight where it connects to drop.

As I asked biggles, if I need new supply and return trunks, what size should they be? The 4 supplies currently come directly out of the plenum...no other supply trunk. I saved all of the original ductwork, so if needed I would have it.

Thank you for your time BeenThere.
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Old 01-24-2009, 11:09 AM   #6
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Many people still think that a ductulator tells then the static pressure of the duct.
It doesn't, it tells you how much pressure it takes to over come the resistance of the duct.

To get 300CFM from an 8" round duct, your supply static would need to be close to .4" wc at the inlet of the duct(unless its exceptionally short).
Which is too high.

You would need a manometer, weather digital, or a u tube, wouldn't matter. To check the manifold gas pressure.
Plus a small adapter to connect it to the manifold side of the gas valve.

Where is your air filter.
Is it inside the furnace, or mounted on the outside of the furnace.
Is it sealed, if its mounted outside the furnace.

You can take an incense stick, light it, and run it near the return duct while the blower is on, to see if it draws the incense in, to check for return leaks.

Low temp rise on a furnace, is usually an indication of too much air flow. But your duct description, fits that of a undersized duct system.

So your furnace doesn't have an A/C coil on it?
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Old 01-24-2009, 12:37 PM   #7
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that 12" X 12" return....is it holding the sheet of paper up.if its not ....then its not going back to the furnace.you need to work your duct problem with the fan in the low setting....and shouldn't trip on hi heat limit due to lack of air.i have to ask this question ......down on the furnace with the fan running is it easy or hard to take the access door off to view the fan.it should be sucking the panel.all these duct connections are they all flex on the supply into the rooms.
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Old 01-25-2009, 10:56 AM   #8
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Quote:
Originally Posted by beenthere View Post
Many people still think that a ductulator tells then the static pressure of the duct.
It doesn't, it tells you how much pressure it takes to over come the resistance of the duct.

To get 300CFM from an 8" round duct, your supply static would need to be close to .4" wc at the inlet of the duct(unless its exceptionally short).
Which is too high.

You would need a manometer, weather digital, or a u tube, wouldn't matter. To check the manifold gas pressure.
Plus a small adapter to connect it to the manifold side of the gas valve.

Where is your air filter.
Is it inside the furnace, or mounted on the outside of the furnace.
Is it sealed, if its mounted outside the furnace.

You can take an incense stick, light it, and run it near the return duct while the blower is on, to see if it draws the incense in, to check for return leaks.

Low temp rise on a furnace, is usually an indication of too much air flow. But your duct description, fits that of a undersized duct system.

So your furnace doesn't have an A/C coil on it?
The filter is mounted on the outside of the furnace, then the drop is connected right after that. I may try to get some images up if I can provide decent lighting.

Thanks for the tip regarding checking for leaks. Lastly, there is no A/C coil in the furnace that I am aware of. You would not have believed how they had the mega mess a/c connected to begin with.

So at this point I don't need to be concerned with building a new square box trunk line?
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Old 01-25-2009, 10:58 AM   #9
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Quote:
Originally Posted by biggles View Post
that 12" X 12" return....is it holding the sheet of paper up.if its not ....then its not going back to the furnace.you need to work your duct problem with the fan in the low setting....and shouldn't trip on hi heat limit due to lack of air.i have to ask this question ......down on the furnace with the fan running is it easy or hard to take the access door off to view the fan.it should be sucking the panel.all these duct connections are they all flex on the supply into the rooms.
In regards to the 12" return holding the paper up? I don't understand. When I place a piece of paper over this return, the paper is drawn down to the grille surface from 1" above it.

I will get back with you on the door cover.

No flex at all.

Thank you both for your responses.
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Old 01-25-2009, 12:47 PM   #10
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Post some pics.

Then we can see better what your working with.

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