# HVAC + HT= Noise?



## memarcus (Jan 28, 2010)

I will be installing some sort of HVAC in my theater next month or so and am concerned with the noise it produces. It has been bothersome since the house was built. The HVAC contractor installed a high static blower so when it reaches full speed on the ramp up, it's quite loud. Heaven forbid anyone does any proper Manual J and D calcs any more.

Anyway at night, when no creature is stirring, the noise floor in my house is about 48dBA on my uncalibrated, roughly handled CM-140 mic. When the HVAC comes to full speed is is 51dBA. I have read that 3dB is sometime considered barely noticeable although it's actually twice as loud, but that must be at 100dB. At this level my HVAC sounds like the shuttle taking off. It's also a very annoying hiss like an open airline. not sure what my vent velocities are though, prolly just shy of Mach 1.

since I can't have this in my HT I'm looking for proven solutions. I have looked into the duct mufflers and they post decreases of about 25dB in the midrange frequencies and a bit less down to 125Hz, but no info after that. Anyone has any experience with these? 

Since I'd like to isolate the best I can is there anyone out there that could post pics of their successful built dead vent? I have room to build fairly large boxes for supplies and returns if need be but not sure how to dimension and deaden. Was looking for how to info and if it's out there, plots showing effectiveness. Was thinking of building a box that increases area relative to the supply or return size, snaking it around like a rat maze, and having the walls out of parallel and lining it with 3" acoustic foam or similar. however I have concerns about home grown solutions what the inspector will allow based on fire code and such. I generally prefer DIY, but if doesn't work much better than off the shelf why bother (other than expense). does this sound like a recipe for wasted time and effort? What can I expect performance-wise?

As a fail safe, is a mini split the gravy train with really quiet biscuit wheels solution? not sure I have the funds for that but it never hurts to price one, just wondering if they're the best solution (money aside). the HT is underground on two sides with double walls and insulation on the other two and a fully floated ceiling with plenty of insulation. It really shouldn't require a whole lot of heating or cooling maybe like 1/2 ton or whatever the smallest unit they make is would suffice I'm sure.


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## Ted White (May 4, 2009)

If you or anyone else cares to send me a PM with your email address, I'll send over a few articles on the subject


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## sga2 (Nov 14, 2009)

Ted - I'm going to PM you my email for those articles. 

Marcus - Manual J? Manual D? What's that? Just kidding... Actually, the ductless splits are a good solution if you need capacity. But they can run upwards of $3k per ton depending on location, installation requirements (refrigerant pipe routing, circuiting for power, etc.). And they are indeed very quiet. However... if you have the capacity already there in the existing system (do you?) and just need to quiet it down, there are more effective (and cost effective) ways to achieve the desired results without breaking the bank or violating Code. Though much of this depends on where your unit is in relation to your HT (though, if it is so close that sound treatment in the duct will be tough then a ductless split is probably not going to help much anyway...). Read through Ted's articles and, when you have a chance, follow up with some info on your setup - room size, location/size of HVAC equipment, ductwork, air devices, etc.

Regards,
sga2


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## Ted White (May 4, 2009)

Groovy


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## memarcus (Jan 28, 2010)

Room is 14.5x21x7.5. Heavily insulated on 5 sides (2 sides also underground) and the floor is over dirt. Seems I wouldn't need but 1/4 or 1/2 ton of cooling but 3/4 is the smallest mini split they make and I believe I'll go that route. I have a friend who works at an HVAC supply house and he can get me an LG unit at cost. So I'll install and then call the hvac guy out to suction the lineset and release the refrigerant, about $1200 tops and about 6 hours. I read through the articles Ted sent and think for the money and mostly the time I'd rather go with the mini split. With materials I felt the dead vent would be at least $500 plus more time building, plus there needs to be two, so $1000 plus lots of time. Seems if you're willing to install, the minisplit wins hands down. I'm going with a more expensive model but there's generic ones available on amazon for about $600-700 which is cheaper than what I'm paying.

I have a closet on the north wall I could build a dead vent in but I don't really have a suitable location for a deadvent on the return. also I'm going to have two subs with 8" ports in them so I just can't be convinced how a couple of 6" holes can isolate low freq content no matter how much you line the things. No penetrations is better and that's what the mini split provides so I think that the way I'm gonna go.

I appreciate all of the help and advice. without this post the possibility of mini probably wouldn't have crossed my mind, but it seems the best solution to my situation.


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## Ted White (May 4, 2009)

I like mini-splits


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## memarcus (Jan 28, 2010)

I like that you like mini splits. Makes me feel good about my decision.


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## Ted White (May 4, 2009)

We recommend them all the time


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