c4qeizlr

Hi there,


I had a contractor install a new set of HVAC 2 years back:

- replaced old 85% gas furnace w/ 95% efficiency 60K BTU variable speed 2-stage Heil furnace
- installed new Bryant 3 ton legacy single-stage air conditioner + AC coil


A few things I'm trying to tackle right now:


1. The blower from the furnace is two-stage. It is capable of handling two-stage air conditioner. The air conditioner however is a single-stage unit.


Problem: noisy cabinet.

Since the air conditioner is single-stage, the output from the thermostat is connected to the Y/Y2 (2nd stage high-speed fan) input on the furnace unit.

The furnace is installed around the corridor corner in a hallway. When the blower pulls air from the vents on both sides of the wall, it's very noisy.

I want to reduce fan noise.


Idea:

I wonder if I can connect the thermostat's cooling switch output to Y1 (1st stage low-fan speed) input on the furnace unit.

This way, the blower fan would always be at the lower-speed. This would significantly reduce the noise around the cabinet.


The only thing I wonder is whether this would reduce the efficiency of the air-conditioner, as the fan is blowing at low-speed while the air-conditioner compressor is working always at full capacity.

Or, it'd just be colder air blowing out slower?

Anyone would know?


PS: Someone suggested to make another opening in the living room area and lay out a pipe to that spot. The piping would drastically reduce the ventilation noise even at high speed.

However, I'd prefer not to make an opening on the floor.


2. There's a leak thru' from the exhaust pipe down to the furnace. In the installation, the HVAC installer used an existing roof vent (cone-shape) by sliding the exhaust pipe into that vent. On the top of the roof vent there is an L-shape PVC pipe he added to direct the exhaust air to point horizontally.

I wonder where the water leak is coming from? I never saw this leak from that vent for years--until after he installed the HVAC unit.



3. I am seeing a LOT of dust coming out when I turn on the HVAC unit (heat or AC). I never saw such an enormous amount of dust before with my older furnace.

The air ducts are in the attic. The installer did not replace any of the air ducts in the installation.

There is an air leak along the edge of the back of the AC coil where it meets the furnace unit. The HVAC installer did not put seal tape along that edge. Would that cause that much dust? The HVAC installer said he was not able to seal that edge up during the installation as it was in the back of the new furnace that he installed. The furnace/AC coil is in a cabinet in the corridor.


Thx.

paul52446m

I don't know what blower speeds you have, but if you are running 3 tons of cooling than you need to be moving 1200 CFM of air.
If you are getting more dust now than you use to it might be because you are moving more air than you was before, so you are cleaning out your ducts.
If you have air leaks than you should seal them up.
Most furnaces have about 4 speed so you can select the speeds you want for heating and cooling. If you run the cooling speed slower than 1200 than you can start freezing up the coil.
If you have noise problem than maybe someone did the return air wrong.
Do you know the blower speeds? Yi is for single stage cooling as long as you are running the right speed. Paul

c4qeizlr

Thx much for the ideas.


For CFM and Fan speed:
The Heil model # is H9MVX060F12.

You're right there are 4 fan speeds. I read the install manual and it stated that the 'speed taps are set based on a nominal 400CFM per ton cooling and the basic mid range on the temperature rise for heating.'

I looked further, and found the 'Circulation Air Blower Data' for the model.

http://icpindexing.toddsit.com/documents/086477/44071202403.pdf
(see page 3 for the *9MVX060 model Air Blower data)


I checked the DIP switch settings for the fan speed setting on the furnace circuit board, and it's currently set at the factory setting for High Speed (*00) for cooling, which means 1239 CFM for High-Cool and for Low-Cool it's 991 CFM (80% of high cool) if I'm reading right.

Are these the correct data I can use?

So if like I thought before, energizing only the 1st-stage Low-Cool setting always, the air-flow would be 991 CFM?


Would that have any undesirable effect when the 3-ton compressor is operating at full capacity (e.g. coil freeze)?



For cabinet noise:
I had this noise problem with the older furnace also. The old furnace was a Lennox 80% furnace.


The furnace sits vertically in a cabinet at the corner of a hallway corridor. There are two 26" x 12" size vent holes at the bottom of each wall corner that allow return air to be pulled into the bottom of the furnace where a filter is positioned to filter the incoming return air.


I wonder if these two 26"x12" vent holes for the return air are good enough for the 1239 CFM air flow when the fan is on high speed?
(these large vent holes on the two wall corners have lattice-like wood covers so the effective vent size would be smaller)

The noise issue was there with the older furnace as well. It just seems w/ the new furnace the noise is same.

I've talked to two HVAC contractors, and they both suggested to install a duct piping in the crawl space and then get return air from another opening (floor opening). The duct piping will eliminate the noise according to these two HVAC contractors.


*** BTW, two additional questions:

1. For heating:

If I set the thermostat to SS (single stage), it'd always only energize W1 (Low-Heat) setting regardless of how long it needs to heat the house to get to the desired temperature.

Would that be ok?

As this would mean having the low-heat secondary heat exchanger operate continuously for extended time (if I need to heat up the house in the morning the first time, it'd take about 45min to gain the needed 10F) -- would that be overburdening it?

Would that cause any undesirable side-effects? (overheating any other components when running the low-heat exchanger continuously for 45 mins)


2. I keep seeing aluminum foil-like pieces coming out of the air duct vents from time to time. I never saw these w/ my previous old furnace.

The air ducts in the attics are paper-like air ducts so I don't think these aluminum foil pieces are air duct materials.

Would these be from the new furnace?


Thx much for help.

paul52446m

Normally we do like to run 400 CFM per ton of cooling You could probably get by with the 991 CFM It will not hurt the compressor, In your indoor coil there are points that get down close to the freezing point, so if you have a lot of humidity in the house the slower you run the blower the more water you have running down the coil, and this restricts the air flow more yet, so the coil could start freezing. All i can say is try it and it may work out fine.
This furnace manufacture of your unit does not know how to rate CFM air flow. Your Cfm air flow that you get from a blower depends on the static pressure of the restriction of you hot air and return air ducts, size of the filter, and size of the indoor coil. How many turns in the main duct, how are those turns made. When we are done putting a system in we can take a pressure reading on the ducts and then then look at a blower performance chart to see how much air that blower will move if i was on the different speeds at a static pressure of maybe a .03 or what ever are reading was. Then you also have to figure out what the average humidity would be. The blower can't move as much heavy humid air as it can dry light air.
The two 26x12 return openings are big enough to let enough are go through the furnace. They make a lot of noise because they are just through the wall.
I call that cabin stile. The open size of the return for 1200 cfm should be at least 220 sq." That is not the size of the opening or grill. This would be a actual free opening of the grill.
(( I've talked to two HVAC contractors, and they both suggested to install a duct piping in the crawl space and then get return air from another opening (floor opening). The duct piping will eliminate the noise according to these two HVAC contractors.)) This is true
I don't know what the BTU heat loss of your home is. If you only lo heat you are getting 41,000 BTU out of furnace, and 58,000 on hi heat. It won't hurt the furnace if you get enough heat on the lo to take care care of your heat loss. Paul

c4qeizlr

Thank you so much for the help -- very helpful!


In changing to run the compressor at the lower 991 CFM fan flow rate on cooling, I'm in a relatively dry climate thru'out the year, so hopefully this won't pose a problem of freezed coil... .

I've just tried running on low-heat only today. So far the furnace seems to run ok. Only thing is that air comes out from the supply vents really hot after running for about 45 mins. Don't know if this should be of any concern?



For the return air noise problem around the return air vents,

You said that the two 26"x12" return air vent openings on the walls are big enough, and these cabinet vents are known to be noisy. I wonder if there's a way to reduce the noise w/o re-routing using the air duct in the crawl space?


The only thing between the incoming air and the return air opening on the bottom of the furnace are the lattice-like wooden vent covers (ignoring the filter). Perhaps if there is a different vent cover design so it could be less noise when air goes thru' the two openings?

This is the kind of wooden vent cover on the two wall corners now (sample): http://americanwoodvents.net/wp-content/uploads/2011/08/Grate-Style-Wall.jpg

Don't know what options are available -- perhaps use metal air grills instead of the wooden lattice vent covers (although might not look that elegant)? Would that reduce the noise in some significant way?


One note:
I'm not opening all the supply air vents in all the rooms in the house -- in order to save some energy in some non-occupied areas. Would that pose an imbalanced pressure problem and hence more noise unintentionally?


Also wonder if anyone would know about these aluminum foil pieces that are falling out thru' the air vents periodically -- just getting me a bit worried... .

paul52446m

I think we talked once about temp rise across the heat ex changer, so if you run low all the time and you are over heating your furnace, you will lose eff. and damage your furnace. The furnace is designed to run a short time on lo, then if temp doesn't come up it will kick into hi and bring it up.
You are trying to salve a noise problem, and you never will by changing a grill or something easy like that. Unless you have lots of room to put insulated baffles in, and maintain 200 sq" then you need to re duct.