[Greg_63]

Be very careful about the modifications that you make to your HVAC system if you don't understand airflow and how your HVAC system works. You can reduce it's efficiency, reduce it's life, damage it and even kill your system.


There is one phrase that he used in that article that has me concerned. He said that there was a sucking sound when he closed his new door. This suggests to me that there was a problem with his system and he has made it worse. I think he has caused a situation that WILL damage his HVAC system and cause premature failure.


It appears that he has a heat pump. If this is the case then he hasn't created a dangerous condition that could put his life in danger. If he used gas for heat then he probably would have created a dangerous condition if what he did wasn't done properly.


Of coarse if his noise is only the noise that the unit makes under normal conditions when installed properly then the mods he did are perfectly fine. The sucking sound he hears when closing the door suggests that the unit has bad airflow and he made it worse. Insufficient airflow will damage an HVAC system.


Most noise from your HVAC system is usually due to poor airflow. Poor airflow is typically due to improper installation of the ducts. Many HVAC installers install ducts that are too small according to manual D. Manual D is the bible for residential duct design. It has standards for allowable air velocity for the different duct materials. I rarely go into a house and find that those standards have been followed. If followed the air noise coming from the HVAC system is substantially less.


I get comments all the time about how much quieter my installs are compared to what they had. They also find that they are more comfortable through out the house.


DO NOT make any modifications to your HVAC system unless you run it by a qualified (licensed) person that can look at your system. There are many things that have to be considered that you don't know about. Even small mods that you might think are insignificant can cause problems. NEVER enclose your indoor unit unless you know that it is safe to do so.

 

[ChrisWiggles]

Can you link the article so we know what you're talking about? I'd like to take a gander myself.

 

[Greg_63]



Quote:
Originally Posted by ChrisWiggles /forum/post/0


Can you link the article so we know what you're talking about? I'd like to take a gander myself.

http://www.avsforum.com/avs-vb/showthread.php?t=845733

 

[ChrisWiggles]

Thanks!


YEah, that caught me as strange too, I have my furnace in a room adjacent to my HT, and it annoys me because I have a large slotted vented door which is needed. Having a solid door would cut the furnace noise a ton, but you apparently have to have airflow into the furnace room. I don't know anything about HVAC, but my understanding is that you can cause serious problems if you seal things up like that, but it was not clear what his situation was in the article. I know the furnace has to vent to the outside as well, but I was pretty sure that it needed to have fresh air into it as well or you can end up with CO going places it's not supposed to, threatening your life.

 

[BIGmouthinDC]

I looked real hard at the picture and it doesn't look like any combustion is going on in that room so the solution is a lot easier than those of use with gas burning anything.


The exception would be those water heaters and very high efficiency furnaces which bring in their own air supplies by separate venting to the outdoors.

 

[usualsuspects]

My utility room has a solid door and no vents between it and other rooms. I have an electric water heater and a gas furnace. The furnace has two 3 inch PVC pipes - intake and exhaust. My contractor pulled all the needed permits when he finished the space, and the final inspection was good - no problem with how it was done as far as the inspector, but I wonder if it is really OK to do it this way?

 

[Greg_63]



Quote:
Originally Posted by usualsuspects /forum/post/0


My utility room has a solid door and no vents between it and other rooms. I have an electric water heater and a gas furnace. The furnace has two 3 inch PVC pipes - intake and exhaust. My contractor pulled all the needed permits when he finished the space, and the final inspection was good - no problem with how it was done as far as the inspector, but I wonder if it is really OK to do it this way?

It sounds like your furnace is a 90% furnace. Those can be set up as direct vent. Depending on the length of the intake you can run it all the way in 3". If the run passes a certain length then you have to increase the size of the intake. You don't have to worry about combustion air coming from inside the house so you can place the furnace in a confined area.

 

[Greg_63]



Quote:
Originally Posted by ChrisWiggles /forum/post/0


Thanks!


YEah, that caught me as strange too, I have my furnace in a room adjacent to my HT, and it annoys me because I have a large slotted vented door which is needed. Having a solid door would cut the furnace noise a ton, but you apparently have to have airflow into the furnace room. I don't know anything about HVAC, but my understanding is that you can cause serious problems if you seal things up like that, but it was not clear what his situation was in the article. I know the furnace has to vent to the outside as well, but I was pretty sure that it needed to have fresh air into it as well or you can end up with CO going places it's not supposed to, threatening your life.

You do have to supply a sufficient amount of combustion air to avoid creating a dangerous situation. It sounds like your combustion air is designed to come from inside the house. However, you can bring in outside air and then you won't need to have your combustion air come from inside the house. That would allow you to seal the room.


I can't tell you how to do it because I can't come look at your set-up and I'm not licensed in your state. I would contact a local HVAC company and see if they can help you supply outside air to your unit. It's not that hard, depending on where your unit is located, and most of the time it's not that expensive. It's definitely worth the cost if the noise is troublesome. Also pay the extra money to have it inspected to ensure that it was done properly.

 

[Milt99]

Chris,

If you need a good HVAC guy in the Seattle area, pm me.

Right now would be a good time to contact one as the "slow" time for HVAC guys is soon coming to an end and you might have a tough time getting one to do a small job such as yours.


As Greg said without seeing your room it's impossible to state specifics but more than likely it involves cutting a hole through the exterior wall and running a duct to the furnace enclosure. The furnace guy would know the proper duct sizing, material, etc.

The only issue might be if your house is brick, then you'd likely need a access to a chimney.

Greg can correct me if I'm wrong, but installing an outside air input can actually improve the performance of your furnace and heat circulation.

FWIW, I'm not an HVAC guy but I've dealt with these exact issues in 2 houses.

Not really difficult but as always there are rules that can't be fudged if you want a properly functioning system.

 

[hevac]

The unit in the picture looks to be an American Standard or Trane a/c air handler ( same manufacturer) and does not require any air from the surrounding area for combustion to work - it is not a furnace so you can totally enclose it. Just leave enough room to pull the blower out when it breaks or you need to maintenance it like changing the setting for blower speeds. I would advise putting in filtered return grills to help with noise. You must have the ductwork sized correctly.


If you have a furnace that uses air from the space for combustion I suggest you change it. It is probably only 70 - 80% efficient and loud. If you do not want to change it call a heating tech he should be able to install a small blower to the out side that will turn off and on with your furnace to supply the air required for combustion and also not let the furnace start if the blower does not start. DO NOT TRY THIS YOUR SELF. A furnace needs a certain amount of air for combustion and it is different for every furnace. If the furnace cannot get the required air from the space it will pull the air back out of the flue. Most system returns or supplies are not air tight so the air from the flue will leak into your system and we may not hear from you again.


The new 90+ furnaces are of course more efficient requiring less space, it gets combustion air from the outside. They are also insulated better and quieter.



I have been in the HVAC trade for over 25 years and am still learning. I have made similar suggestions in other threads and will probably get **** for these but here go's anyway.

Make as many 90's as possible, 4 minimum in both return and supply main trunk lines. All ducts must be interally insulated. Use flex for supplies. You can shape them in s shapes to stop noise travel. If you need 2 8" ducts to cool or heat the room double it to keep air velocity down. Keep supplies high on the wall or in the ceiling. direct all supply air across the ceiling to eliminate the feel of drafts when the system is running. Put returns Low and near the front. Put balancing damper on the supply at every take off run, again to balance the system. You would not believe how many systems do not have these cause the installer thinks he's so good they are not necessary, Bull ****. They cost a lot less at the time of install then later. Put a damper in the return at the unit. T his is in case you cannot get enough static and or restriction on the supply side of the system. You are trying to make a HT system quiet. vAlong with static, high CFM & FPM comes noise. vMost of the duct sizes you will be using to keep these issues under control and are made to handle 2 to 3 time the air flow to work correctly and cause the static required for the system. vThe return damper can be used in the same manner as the supply dampers to restric air flow and cause resistace that the unit needs to run properly. vIn a perfect world we would not need resistance or static for a unit to operate correctly but it is not a perfect world.

These are only suggestions and not carved in stone, every system is different.

 

[hevac]

Usualsuspect

It does sound like you have a 90+ direct vented unit. The heat exchanger where the flame is, is a sealed chamber and there is a very little chance if any for the flue gas to enter your house from that system, unless worse case you crack or get a hole in your heat exchanger. I would still install a carbon monoxide detector as I would for any furnace area as well as one on every floor at least. Every house should have CARBON MONOXIDE detectors and in some states like MASS. they are required. You can not even buy or sell a house here without them.

 

[ifeliciano]



Quote:
Originally Posted by hevac /forum/post/0



I have been in the HVAC trade for over 25 years and am still learning. I have made similar suggestions in other threads and will probably get **** for these but here go's anyway.

Make as many 90's as possible, 4 minimum in both return and supply main trunk lines. All ducts must be interally insulated. Use flex for supplies. You can shape them in s shapes to stop noise travel. If you need 2 8" ducts to cool or heat the room double it to keep air velocity down. Keep supplies high on the wall or in the ceiling. direct all supply air across the ceiling to eliminate the feel of drafts when the system is running. Put returns Low and near the front. Put balancing damper on the supply at every take off run, again to balance the system. You would not believe how many systems do not have these cause the installer thinks he's so good they are not necessary, Bull ****. They cost a lot less at the time of install then later. Put a damper in the return at the unit. T his is in case you cannot get enough static and or restriction on the supply side of the system. You are trying to make a HT system quiet. vAlong with static, high CFM & FPM comes noise. vMost of the duct sizes you will be using to keep these issues under control and are made to handle 2 to 3 time the air flow to work correctly and cause the static required for the system. vThe return damper can be used in the same manner as the supply dampers to restric air flow and cause resistace that the unit needs to run properly. vIn a perfect world we would not need resistance or static for a unit to operate correctly but it is not a perfect world.

These are only suggestions and not carved in stone, every system is different.

If we place dampers in all the takeoff in the blower's plenum, what CFM of FPM do you recommend at each supply register ? How much do we open or close the dampers to make the system efficient. ?


I'd like to install dampers in all my system's takeoffs, but don't want to tax the system in anyway.


Ivan

 

[hevac]

ifeliciano

No more than 200 fpm or 100 - 150 cfm from an 8" round flex duct. This is why you need dampers on the main trunk where the supply take off starts. If you try to control the airflow at the register you will probably get the register to whistle and that worse than air noise.

If you here noise from the supply register adjust the damper till you do not but must still have air coming out of course. Like I said earlier you must run more ducts so you do not limit air flow down to a level that could damage the unit.

FPM stands for feet per minute, which is easier for DIYers to measure. A meter to measure FPM is not as expensive as the next item. CFM is much more complicated to measurement and usually requires a qualified balancer or much more expensive measuring equipment. Duct work is usually sized by CFM. But low to moderate noise is not usually a problem under normal conditions

 

[Greg_63]

I'm not going to debate all of the advice given here today but I will make a couple of comments.


Never put any more bends in your supply duct then you have to. Both the main trunk and the branch lines should be run as straight as possible. Bends in the supply greatly reduce the efficiency of your airflow. The way to reduce noise on the supply side is to use larger supplies. Of coarse if you go too large then that isn't good either. A properly designed duct system (and most aren't) is based on the needed CFM for each room AND overall FPM based on the CFM being delivered by the unit.


As for FPM 200 is too low, way too low. You will not get enough airflow to cool or heat the room. You should have at least a little more than double that and it will still be fairly quiet. HOWEVER, if your whole duct system isn't designed for this then it won't work properly using dampers. What you can do is if you have a 6" duct that is too loud and you want to make it quieter then increase the size of the branch line after it comes off of the main trunk. Increase it to an 8" line and change out the boot and the supply grill. This will decrease the supply noise at that register with little to no effect on your over all system performance.


Almost all duct systems that I see have higher FPM then they are suppose too on both sides of the system, supply and return, according to manual D. Too high on the FPM and the system runs loud as well as putting more stain on the equipment. I usually rip out the old duct and after I install the new duct, main duct sized using FPM based on the CFM of the unit installed and branch lines installed based on needed CFM for each room at the FPM available, my customers are surprised by how much quieter the system is and how much more even the temp is throughout the house. You maintain the FPM throughout the system by using a reducing main supply.


BTW, an 8" supply will deliver 200 - 240 CFM at 600 - 700 FPM and still be fairly quiet. Remember that you still want to be comfortable.


As far as noise on the return side these are the factors that will cause a return to be quiet. The return grill must be large enough for the return duct size and the return duct must be large enough to keep the FPM less than 700. Using flex will help and putting bends in the return will help but if the return is sized for less noise to begin with then these aren't needed. The bends might be needed if the location of the return is close to the unit. Then bends will help reduce the noise coming from the unit through the return. However, most returns are noisy because they are too small and the noise you are hearing is from the air movement and not the unit.


In Mass returns low but in hotter climates returns high. It all depends on what your system needs to be optimized for, heating or cooling. Where your supplies and returns are has nothing to do with the noise level. The size of the overall duct system is what determines the noise level.


NEVER restrict your return. Your return is probably already too small. I have never gone into a house where the return was too large. The system will build the needed static if your supply side is sized properly. The larger the return, the quieter it will be. Restrict it and the noise level WILL rise. This is for most systems on the market. Some of these very high efficiency units only achieve those high ratings if the whole system is perfectly installed right down to the type of grills you use on both the supply and return sides. Those systems are sold through a lot of BS. The payback on them is not worth the extra expense but that's another discussion.


FYI, flue gasses from any unit that is getting enough oxygen for combustion will not contain carbon monoxide. This is why it's important to make sure that your unit is getting the required airflow for combustion.


The bottom line is that you need to know what you're doing before you make any modifications to your HVAC system.


BTW, I agree with a lot of what hevac has said.

 

[hevac]

Greg_63

I agree with most you have said also.

If you do not use 90's and you keep the duct straight how are you going to control the noise from moving from register to register through out the system especially in a zoned system? I have customers that are very sensitive to noise in general and that includes air flow noise. It is even worse when they are listening to their 2 channel systems. That is why I run 4 8" ducts instead of 2 if the load in the room requires that much air to cool the space.


I only suggest the return air damper if DIYers are doing the duct work and over size the supply thinking bigger is better and that is a big no no for a proper a/c system. You can only get out what air you put into the system. The damper in the return can help instead of redoing the duct work after everything is closed up. I know it is not perfect but I have seen a lot worse. Like cutting in a supply at the end cap of the supply duct & can't figure out why nothing or very little air comes out of their old registers any more.