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Old 06-22-2009, 08:37 PM   #1
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Sound Transfer Through Heating Ducts


I'm a homeowner looking to update our oil furnace to an air heat pump. Our 1950 house is a 1200 sq ft rancher style with an 800 sq ft suite in the basement. There are hardwood floors on the main floor and tenants up and down have complained about noise, and voices transferring through the floors. It's hard to say how much of the current sound transfer is coming through or between the joists and how much is coming through the vents. I will be living there one day so I take the sound problem seriously.

I'll be adding Roxul and sheetrock with resilient channels to the basement ceiling, but I hate to spend the estimated 10 K on the heat pump and 3 K on installing sound insulation only to discover that sound will pass along the heat ducts. My option is to not have any heat vents servicing the basement, and using baseboards for that level, but it defeats the purpose of getting an energy efficient heat pump if it's still going to cost us a fortune for electric heat downstair. (I'm paying the utilities).

I'm wondering, for example, if adding soundproofing within ducts or some kind of baffle would help.

Your thoughts are appreciated.

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Last edited by akimbo; 06-23-2009 at 12:41 AM.
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Old 06-23-2009, 12:25 PM   #2
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Sound Transfer Through Heating Ducts


http://en.wikipedia.org/wiki/Soundproofing
I guess you could put baffles in the ducts but then you'd have to readjust the pressure vs. flow rate for the ducts, maybe using a booster fan.
You could also mask voice frequencies with a white noise generator. Turbulence in the duct air flow might accomplish the same purpose. Most of the intelligibility in speech is above 1500 Hz.
If you have a phono cartridge w/amp. you might be able to find out how the sound is transmitted, whether structurally or through the air, by touching the needle to various surfaces. You could use a radio tuned to an all-talk station for the "test signal".

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Old 06-23-2009, 12:41 PM   #3
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Sound Transfer Through Heating Ducts


Have you listened at the ducts in the house to hear if the noise/voices are coming from them? The Roxul fiberglass insulation should cut down a lot of the noise and insulated ductwork should help also. One of the (few) benefits of insulated flexduct is that it absorbs noise (I'm guessing your new forced air heatpump system will have an insulated metal trunkline with insulated flexduct branchlines).
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Old 06-23-2009, 02:34 PM   #4
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Sound Transfer Through Heating Ducts


Thanks Yoyozit and sktn77a. I like your radio station idea as a test signal. Regarding baffles, I've had one quote with an actual visit to the house and two telephone quotes with other HVAC companies and, while they all agree that sound transference will be a problem, only one of them mentioned baffles, but didn't know anyone who does this. Furthermore he said that adding baffles would make tweeking the air pump flow much more complicated, so he discourage it. I find it hard to believe that, in a city of 350,000, I'm the first person ever to have this concern and that there is so little expertise.

My quote of 10K for a 2.5 T Lennox XP15 incorporates the old ductwork so I'm near the limits of my budget. I'm told that our local sheet metal fabricators earn more than brain surgeons so will only be getting only the absolute essential additional ducting.

We won't know the condition of the old ductwork until we tear open the basement ceilings (I have to do that anyway because the code is for drywall ceilings and currently there are ceiling tiles). But I expect to find some problems because there is currently little or no air reaching some of the rooms upstairs. I'm told that there is a lot more air flowing with a heat pump system so I hope that even with the old ducting we'll get air into the cold rooms. Regarding flexible ducting, I read that it is to be avoided because it doesn't carry air as well as the solid ducting, but if I can get a hold of the insulated flex ducting, that might solve our sound problem.
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Old 06-23-2009, 03:59 PM   #5
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Sound Transfer Through Heating Ducts


Well, flexduct is pretty much flexduct. If you can avoid it, do so. But if you have to use it, it should be a little quieter than sheet metal.

Your sheet metal worker story sounds like my plumber story - When I found out how mucbh my plumbing bill was, I said "Sheesh, I'm a doctor and I don't make that much". Plumber said "Neither did I when I was a doctor"!

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Old 06-23-2009, 05:38 PM   #6
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Does your code for multiple dwelling units allow for common ductwork? Seems like the answer is two systems - or don't they have multiple split systems (one outdoor unit feeding two or more air handlers inside)?.
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Old 06-23-2009, 07:08 PM   #7
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Hey sktn77, That's funny!! To 'jogr', no I don't need to have separate ducts to meet the code, just a common smoke alarm connection, but separate would be ideal, if I could afford the sheet metal work. I've ruled out the ductless split because it doesn't provide a backup for when temperatures dip below the heat pumps capabilities, plus they are much more expensive, by the time you route refrigerant and electrical through all the walls and the rooms--or so the company that sells them said, i.e. they discouraged it for my needs.
Well, I can always cap off the ducts going downstairs and they'll have to run electric baseboards, or else I'll try to get my hands on some insulated ducts. Thanks.
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Old 06-23-2009, 07:22 PM   #8
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Are you getting a new air handler with that heat pump? What is the model # of it, I sell Lennox. You won't get better air flow with a heat pump. Only a better furnace blower/air handler blower will help. I would get your ceiling tiles tested for asbestos B4 removing them. In those days that was common. Sound travels in straight lines so it won't travel like a snake thru your ducts. You can have them insulated externally with insulation with a foil backing which may help. Filling the joist spaces with insulation is the best bet.
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Old 06-23-2009, 07:51 PM   #9
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Hi Yuri, Here are the specs for the quote I got: Lennox 2.5 Ton XP15-030 heat pump, CBX32MV-030 fancoil with 10kww electric back-up heat, and a digital heat pump thermostat. They are going to remove my old oil furnace, but not the oil tank.

Yes, we are going to fill the joist space with Roxul 'Safe-n' Sound' and add at least one layer of drywall over resilient channels. Oh, I sure hope those ceiling tiles are not asbestos. Take a look at these pics.
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Old 06-23-2009, 08:41 PM   #10
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That is a very good package as the air handler has a variable speed ECM blower which can help improve your airflow. The only way to know about the tiles is to remove one and have it tested by a lab. Check "environmental testing labs" in the Yellow pages. No joke, flooring and other materials used asbestos as a cheap filler, you don't want to live with that dust so I would get it checked. Why would you want to leave an old oil tank, it is a environmental hazard and you may have a big problem later selling the house with it due to the environmental laws. I know it is expensive to remove but it should be done. If it is underground then you need to contact environment Canada or whoever makes the rules about how to deal with it. They keep records of who has/had them so it has to be dealt with. My relatives live in Abbotsford, I went on a kayaking trip in the Johnston Straight to see the Orcas, good times.
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Old 06-23-2009, 09:26 PM   #11
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Sound Transfer Through Heating Ducts


Hi Juri, I'm not planning to leave the oil tank. It's just not part of the furnace deal, probably because it will cost a bundle to get rid of, although it's above ground. But I sure won't be sad to see that oil-sucking furnace go. Glad you think our furnace bundle is a good one. What do you think of our sound dilemma?

We are in Vancouver, but the house is in Victoria. The guy renting our house takes people out sea kayaking if you're interested.
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Old 06-23-2009, 09:38 PM   #12
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I don't think you have a sound dilemma. The difference is that people got used to carpet muffling the sound and now that hardwoods are popular they have to tolerate some sound. Impossible to have total quiet. Or lay down some nice shag and problem solved. That is a very good quality package you have. I hope the contractor has a velometer and can balance the ductwork for you, the blower has lots of adjustment/fine tuning features. Make sure you get it cleaned and serviced once a year. I would buy the matching 10 yr labor warranty to go with the 10 yrs parts on the heatpump and get it for the airhandler. It is cheap insurance and unlike some sleazy competitors/operators, Lennox purchases it thru an insurance company (Equiguard or Complete Care) make sure you get a certificate from them. You may be eligible for the 15% home improvement rebate for purchasing a new furnace from the Federal Gov't. Check with BC Hydro for any rebates they have also. I may go kayaking again in a couple of years, got to get in shape for that.

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Old 06-23-2009, 11:52 PM   #13
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The quote included a 10-year parts and labour warranty, and yes we expect to get almost 2K back from the province and the feds (off the 10K, including taxes, price). Still, its a fair chunk of change. It's all hardwood upstairs so expect there will squabbles between upstairs and downstairs tenants unless we can try some of the above suggestions, but I guess we'll just have to see how it goes. Thanks.
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Old 06-23-2009, 11:54 PM   #14
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. . . however, having just read a lot of information about asbestos tiles, and being pretty sure now that we have asbestos ceiling tiles throughout our basement, my sound problem has just been eclipsed by this giant new headache.
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Old 06-24-2009, 02:53 PM   #15
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Quote:
Originally Posted by akimbo View Post
. . . however, having just read a lot of information about asbestos tiles, and being pretty sure now that we have asbestos ceiling tiles throughout our basement, my sound problem has just been eclipsed by this giant new headache.
Just have the HVAC company take them all out when they re-do the ductwork. It's probably not asbestos and you can spend a lot of money just finding out that they aren't. Not sure how it worked in Canada but there are next to none of those old asbestos containing tiles left here in the US.

Beware of what you read on the internet and, remember, the information is worth about as much as you are paying for it!

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