HVAC Flow Problems

Can you reduce the air flow to the other rooms to get the desired flow rate to the MB?

Buy a cheap air flow meter and balance the system. This could take some time to do properly.

I assume you have checked the duct work for obstructions?

I'm no expert but it seems simplest to install in the duct, just before the vents into your bedroom, a fan with the pressure side facing toward the bedroom vents.

j.

I think your problem is air balancing and adjustment of air flows. I recommend to let the entire ducting system be check by a Commissioning Contractor who is specialized in air testing and balancing. They will do everything and solve your problem. okay.

graysurpa

That is one thing that I have not; checking for obstructions in the duct. As the ductwork is not easily accessible how would I do that?

Thanks

Sounds like it's time to call the man.

There might be a blockage? Look at the size of the piping or ducts. If the duct he used to the new room is smaller then the others you will have to adjust all others to try and force more air to the master badroom lines. Start with all others closed and the master bedroom full open. If that doesn't work then you have open lines in the walls.

Mr. Stick Stuff

stickstuffgrip.com

How old your HVAC system?? If you have any as built drawings or commissioning report check the supply air quantity and verify it with actual air supply with the help of anemometer.

Once air balancing is disturbed to restore it we have to check all the previous calculations and verify it. There is no short cut way for this.

You can refer NADCA documents for understanding the duct cleaning requirements.

Good answer, the only thing I would add to it is that it might be possible to increase the blower speed, this would do nothing to increase the available capacity as far as heating and cooling, but it might be beneficial in air balancing the system.

The other thing I would add is to make sure that there is a return path. If the bedroom door is closed and is not sufficiently undercut or some other method used for return air, the room could be pressurizing which would reduce the airflow.

I think your original assessment is probably correct, the ducting going to the room and or the register is too restrictive.

PS: if the register in the bedroom is one of the cheap stamped registers, you could replace it with one of the less restrictive bar registers, this would definitely increase the airflow if this is a situation, although I'm doubtful that it would be sufficient to completely solve the problem.

Thanks for your commendation. Yes, it may be possible to increase blower speed and/or upsize the motor. Some units can be switched if direct drive, or if belt drive (more commercial style) then new sheaves and belts can be installed.

I did consider the stamped grilles as you mentioned, but if the grilles are the problem then the increase in airflow should be readily noticeable once removed. You might even be able to reasonably estimate the airflow with a very large plastic garbage bag, a stopwatch and some quick arithmetic.

Finally, yes, the return air path is very important. I have found lack of return air or relief venting in commercial/institutional retro-fits to be a major problem, where the building owner added some ESL classrooms for a new tenant. They added supply air ductwork, but there was no door grille or transfer ducting to allow supplied air to return to the main corridor. The classrooms suffered from poor AC due to no return path and they had to keep the doors propped open to get the system to work.

The Owner of the building cheaped out and hired his favourite contractor to do a design/build without a engineer or good mechanical designer involved. Of course in single family housing, there is rarely any "real" HVAC design done unless the house is high end, architecturally designed.

Residential ductwork is never done very well. There are usually a lot of leaks and it is never designed. They just throw some duct in and hope the air gets where it needs to go. It is also not unusual for them to cap a joist space and use that as your ductwork, as well as tapping into hollow spaces in the walls. You may also find that they have used flexible ductwork for the run outs, and that restricts the airflow by a lot. If you if that you have a lot of flex then you might want to replace that with round pipe, you can get it at the hardware stores. I would suggest that you try and plug up any leaks that you find and replace any flex duct. If that doesn't help you may have to add a new duct run back to the furnace. You never know maybe who ever added the master bedroom might not have made that final connection and the air is just blowing into the wall or something like that. Oh and if you just can't find it yourself and hire someone. My best advice is that you research your duct system as best you can and that why someone can't flim flam you with a lot of bull and sell you more then you really need. The more you know about what you have the better service you will get. Oh and it is also possible that you furnace is just not big enough. Post how many Square feet your house is and all information you can find on your furnace / condensing unit and I can tell you if you have enough capacity.

Good luck,

hi there,,,

not sure where your at on this problem,, but didn't see any suggestions to push a camera in the duct,, they have units you can rent,, small camera on the end of a flex hose,,, and has a video on the handle end to "see" as you push it in the duct,,, can go from both ends if a long run,,

I have ran into this problem several times,, what most installers don't think of (esp home do-it-'rs) each corner you install will add a resistance to the flow,, along with a straight pipe,, there is a chart that will tell you ,, each fitting corner,, etc,, is equal to 'X' feet,, so when your run was installed to the new room,, and use'd 5- 90's and 30 ft of pipe,, even if you shut all the other damper sown,, you still wont get as good of flow as a shot simple run,, looking in the camera will tell you if there is something stuck in duct,,( toys,, shirt,, etc) and/or if it has came apart,, and also how it was installed,, 1- 90,, or 5- 90's,, with this info,, you can make a better decision of how to fix,, like remove the toy,, shirt,, thats a cheap fix,,, (use a fish tape with a hook on it)

or if you have to do the --reinstall correctly--- fix,,

well there is my 2 cents worth,, good luck!

if you have only one system and it is a 2 story house the temperature will never be constant. even with good flow it is very hard to get even temperature. the only place that is the right temperature is in the hall at the thermostat. I suggest installing a mini split system, cost about $1500 and you can control the temp in that room

But what about HVAC for large buildings if we face flow problems in any zone?