Stupid question regarding furnace air flow

MaxMercy

My brother has a two story Colonial about 3200 sq feet. He's lived in this house for over 30 years and has always used a professional HVAC company to service it (he hates to bother family members). Yesterday, his wife called me to check on an electronic thermostat that had battery corrosion. I replaced the battery contacts, repaired the board, and reinstalled. That part is good, and I got to do a favor for a brother who does everyone else favors.

But, their airflow on the second floor registers is very weak, and almost non-existent in a room added over their garage as an art studio. My sister in law says it takes forever for the heat or AC to get to temp in the studio, and it's very slow in the upper floor of the main house.

Every house I have ever lived in or rental I've owned has either been hydronic or hydro-air, so I don't know what's going on. I wasn't able to see in the attic as they only have a small scuttle in a closet that would need to be emptied, so I don't know if there's any kind of air handler in the attic at this point or if there would even be another air filter cut in somewhere for the second floor.

The first floor airflow is fine, but not particularly fast - it's adequate at best I would say. I don't know if the furnace has a multi speed blower, but I do know the two second floor thermostats are three wire (red-white-yellow for heat and AC) and the first floor thermo has maybe 6 wires connected.

In the basement there are three zone valves which seem to operate correctly, but I'll double check to see if they're making a full turn when I go back.

Any thoughts on this system or what I can do to troubleshoot why there's so little air flow on the second floor?

GGross

Silly question but when was the last time the filter was changed?

JUGHNE

Where is the air filter?

MaxMercy

GGross said:

Silly question but when was the last time the filter was changed?

A few weeks ago the furnace was fully serviced.

More info - I just talked to my brother and he says that when the studio was added over the garage, the airflow on the second floor was reduced at that time.

As far as I know, the studio is not tapped from the second floor but ductwork was added back to the basement.

MaxMercy

JUGHNE said:

Where is the air filter?

I assume it's right at the furnace and was replaced very recently. I'll double check when I stop back over the weekend.

Jamie Hall

There are no stupid questions -- only stupid answers. I hope this isn't one, but... how does the air get back from the second floor and especially the studio to the furnace? To paraphrase a steam axiom -- if the air can't get out, the air can't get in.

EdTheHeaterMan

There are no stupid questions. Just stupid people that don't ask questions.
I can say this about air flow. If you want an inexpensive system you can design a system that will have the proper air flow thru the smallest duct that will allow a specific amount of air to move to the rooms. This system will be noisy and you will definitely feel the temperature difference and force of the air coming from the registers. I would call this a poorly designed system that you might find in “Spec Home” buildings

In a custom home you can find installed the same size (BTU Capacity) system, with larger ducts with more outlets per room and the static pressure will be much less resulting in a much quieter system. The same amount of air flow with less noise. This also lends itself to better balancing with partially closing down dampers to some rooms that are unoccupied (or perhaps get too much air flow), without causing more air flow noise to the other rooms in the home. So that being said, I would not jump to conclusions on the lack of airflow. It may just be a well designed system.

That said, if this is a two story home with only one system, and the second floor is harder to cool and the first floor is harder to heat, then you have a balancing problem that must be addressed each change of season.

And finally in my mind's eye, I see a two zone system where the basement ductwork is easily accessible and the attic has an air handler that is only accessible from that closet opening. That Air handler may have an air filter located in the cabinet. Even if there is a filter grill(s) in the ceiling somewhere, the original installer may not have removed the air filter that came with the system. That may be the reason that the second floor system is having so much trouble. If that filter has never been cleaned (or removed is the best idea if there are filter grills elsewhere) then you can have an air flow problem as suggested above.

EBEBRATT-Ed

The ductwork going to the studio from the basement is likely sized too small. Typically going from the basement to the 2d floor provides poor air flow and balancing will not fix it.

The duct is to small it's a long run and probably more elbows.

Perhaps a booster fan wired with the blower motor will help.

This is a very common problem when extending ducts to the second floow. Air like water takes the path of least resistance. Return is probably undersized as well if one exists.

EdTheHeaterMan

I remember a particular duct system that I installed “by the book”. It was probably a 3.5 Ton cooling system with a horizontal gas furnace in the crawlspace. (I was young and stupid then). As it was, this home had a garage next to the home with a utility room that was converted to an office. The foundation was such that there was no crawl space access from the main home duct system to the office. However, customers do not understand the fine points of static pressure and equivalent length and all that other stuff you need to know, to design a balanced system. All he wanted was a duct in the office.

After trying to explain to him that the duct will probably not work, he decided to pay extra for that duct anyway. I then connected a 7” takeoff off of the last section of trunk in the crawl space and attached about 12 feet of 7” flex duct to reach the garage wall. From there is installed a 7” round metal duct thru the box plate into the garage and a 90° elbow with 7” metal duct to the attic. From there I then added another 12 feet of flex duct to reach a ceiling register in the office. At that point the additional duct was completed and I got paid for the job.



Two weeks went by and I called my customer to see if everything was working, and guess what? The office was not getting enough heat. I told him that "I would stop by and check it out to see if there was anything that could be done. However, if you remember, I told you that it probably would not work." The next day I went to look at the job and no one was home. So I went into the crawlspace and adjusted the volume damper I installed on each takeoff to about a 45° angle. This substantially increased the amount of air flow to the only 7” takeoff at the end of the system, while reducing the flow to each room in the main home just a little. Since all the main ducts were reduced equally, the balance in the main home was not affected.

Another two weeks went by with no information, so I called the client and asked if there was any difference? His reply was “I don't know if you were here or not but all of a sudden the office duct is working great now.” I explained that I was there the day after we talked and made a major adjustment and wanted to be sure that the rest of the home did not suffer any problems with that change.

This example illustrates that even without a great design, Your sister's addition may have a chance to work fine with some adjustments. But check the air filters to see if there is a forgotten one inside the air handler or worse yet… the intake side of the AC coil does not have a layer of household duct accumulation. It is not always the easiest place to look depending on the way the system is built. Substantial disassembly may be required to view that side of the coil.

HVACNUT

With only 3 wires on the 2 second floor thermostats, it seems like it might be an old Trol-A-Temp Master/Slave zoned system. (Only the first floor thermostat can switch between heat and cool.)
Look around the furnace for a zone panel and zone dampers in branch ducts. Possibly a Summer/Winter switch.
If that's the setup, it could be a bad damper.

There is AC, so High speed fan is probably connected here. Most furnaces using PSC motors offer multiple speeds. If the heat speed is on Low (usually Red wire), then you can increase it to Medium.
There is a rating listed on heat rise for the furnace, so just make sure it's not out of range if you make a motor speed change.