Would appreciate some help and advice. I live in Iowa (cold winters, hot humid summers and everything in between) and just bought a new house. Itís a ranch with a walkout basement. There are 1980 sq. ft. on the main level and the same below. Nothing is finished yet in the basement. House itself is built wellógood insulation and though I think the windows are not real great, a blower door test indicated .12 air infiltration. I guess that means their ok? Back on point.
Iím not real happy with the heating system. Iíve got a single-stage WeatherKing 92 AFUE 105k output Btuh model 90RJ10EGS01. Iíve got a WeatherKing 12 Seer AC with an Aspen coil. Itís a 4 ton and the model is 12AJA4801. The builder went with a 4 ton because he said that will be necessary if the basement is finished off someday.
The problems that I currently have are noise and the house feels cool at times. Iíve called a couple of places to get some advice and opinions, but none of them seem to have the knowledge that some of you folks have.
The general consensus is that my noise problem is ducting. I thought it was the unit itself and still think that might be part of the problem. The blower sounds loud when I compare it to my parentís lennox which is also single-stage 100k output. Iíve been told my trunk ducts are two small. The furnace is centrally located in the basement and has two trunk supply ducts running in each direction. The one duct measures 8 x 14 and the other is 8 x16 for about 5 feet and then reduces down to 8 x 14 for the remaining run. The cold air return is all 8 x 14.
On another board, I was told the unit is oversized and that is part of the problem. I did a load calc using heatpro and it said I should be more in the 75k output range with a finished basement. The person who said it was oversized also said thereís no way my duct system will handle the 4 ton a/c. The heatpro calc suggested trunks sized 8 x 18. I should mention that all of my supply runs are the rigid 5Ē pipe.
The real issue is that Iím planning on finishing the basement soon. Unlike Jeff, however, Iím lucky in that itís wide open and I can basically change anything I want. Of course it all costs, but I have access to everything. I want to balance comfort and noise and right now both seem a little out of whack. Iím planning on adding five more supply runs in the basement. The only part that seems ok are my cold air returns. Thereís one in each bedroom near the ceiling, one in the living room near the ceiling, and a spot for one in the basement at ground level.
Will adding the five additional runs in the basement help or hurt my situation? Is my ducting really not going to be able to handle the 4 tons of cooling? Are my furnace and AC way oversized? How can I reduce the noise and increase comfort?
I realize this is a short novel, but Iím not touching anything in the basement until I get some good advice. Iím not that confident in the local contractors. Iím looking to you good folks for some advice. I appreciate any constructive feedback you give.
If anyone would like a photo of my layout, Posting your email address is against the Forum Rules Sometimes a picture is worth a thousand words.
[Edited by Lusker on 02-03-2006 at 06:27 PM]
14x8 return for a four ton unit is way to small
it is about 500cfms off the top of my head and you need 1600 min. your supply is small also and imo all the ducts need to be replace with the proper sized
have some do man-d to size the system ducts properly
Airspeed limits per Manual D
The ACCA Manual D method is the most proper way I think, to size your duct system. A really good HVAC technician ought to be able to apply this (though by this definition such techs are hard to find where I live). This book states clearly that using hard pipe, you are best to limit airspeed to 700 feet/min for supply ducts and 600 feet/min for returns. It also states the maximum airspeed approved is 900 for supply and 700 for returns.
If this limit is exceeded, you can expect excessive duct noise. This is not merely academic, I can testify that my own supply ducts are very noisy when my air handler pushes 1400 cfm -- I estimate this makes for 860 feet/min in some of my ducts (flex, which has 600 recommended and 700 max). In my case choosing 1200 cfm gets down to about 750 feet/min, still exceeding the limit and slightly noisy.
As has been said before, your 4.0 ton AC air handler will need to supply about 1600 cfm. If you do some arithmetic you can easily calculate the airspeed necessary to push that 1600 cfm through your ducts. I think you will find some numbers which definitely exceed what Manual D approves.
This is only one part of Manual D, there are other parts which I have far from mastered. But I do believe there is nothing misleading in what I have stated. If any of our professionals care to point out any errors here, we all will benefit.
Best wishes -- Pstu
more help please
Thanks for the responses thus far. However, I really am a novice. I really don't understand all the cfm talk. Are you saying I can adjust the air handler to lower the cfm? Is this advisable?
Also, just so I am clear (my terminology may not be correct), I have 5" snap together supply run pipes. My supply trunks that feed those pipes are roughly 8x14, but the plenum is much larger than that. The cold air return run is the same size 8x14. However, when it gets back to the furnace, before shooting downward, it widens out dramatically. The vertical part that then runs down almost to the floor and then over to the furnace is 10 x 25.5. That part is about 8 ft. tall and runs down then kind of elbows over and once it actually poors air into the furnace it's 16 x 25.5. That's roughly the size of my filter. I didn't want to paint a picture of the cold air return only being 8x14 when it feeds back into the side of the furnace. That isn't the case.
Does that make a difference with respect to some of the previous comments? Sorry to sound naive, but I am. Is the manual D something that a complete novice could attempt to get through?
What has been stated is you need a HVAC Professional/Contractor!!
You need to have them do a detailed room by room load calculation(Manual J)...
You need to have them do a detailed duct layout based on manual D..
They can point you in the direction on if anything you currently have can be salvaged or if all is mis-sized..
PSTU is great guy but not your average homeowner..
I vote that PSTU become a homeowner Pro!! He is more knowledgeable than some techs that have been in the field many yrs.. Great posts Student..
i hear you
I would love to hire a professional HVAC Contractor. Unfortunately, around here there are a ton of contractors but none that I would call professional based on your standards. The places that I have called (three in total) all just spout off old rules of thumb and I'm talking about Lennox, Trane, and Carrier dealers/techs. Now, I'm not saying they don't know their stuff, but none seem interested in doing a load calc for each room and a duct design based on Manual J and Manual D, so maybe they are just lazy.
I think I'll probably just read what I can in these forums and take a crack at it myself. I can't do any worse than the random rules of thumb that I'm being quoted and it'll probably be a step up from every other new const. home around here who uses these guys. At least the HeatPro calc gives me a rough estimate of output I need.
I'd hire a good one if I could find one. There aren't any ACCA contractors within 50 miles of my zip.
I did mispeak earlier. My supply runs are 6" not 5".
There might be a contractor on this site that is near you..
You might want to start a thread asking if any contrators from this site service your area....
Also check the NCI website and see if there are any trained pros from your area..
A proper ductsystem design is tough to do.. I made some major mistakes when I first started doing them and it took me a while before I found out some steps I was not doing correctly.. These mistakes were costly.. Also proper installation of ductwork is not an easy chore.. Metal is sharp and cuts deep.. I know first hand(lucky I still have both my hand left)..
I would not recommend trying to do your own design and install... Will not save you any money and will cost you many times over, untill it is totally done right..
Also, this site will not allow step by step directions over the internet and any that will may not give you the correct advice for your situation as they have not seen the job and may not know how to do it correctly but think they do..!!
DIY in this project is a disaster waiting to happen.. I am sure there is atleast one true hvac contractor in your area,, probably more than one..
Your duct work sounds like a beginners first atempt at design.
With out any trainning.
Tear out and start over.
Get out the phone book and start calling contractors, ask them if they use manual D, keep calling until you find one that does.
Yes, you can buy the books and study them, and might be able to do a better job then what you have now. But a quality contractor will check the sizing of both your furnace and A/C and be able to advise you if its worth while just redoing the duct work.
If your furnace is over sized that much, wonder how far off the A/C sizing is.
That's what's funny about it. They weren't beginners. The company has been in business for over 35 years under the same family ownership.
I don't know much about HVAC, but I know a little more than the average homeowner. I think most folks out there don't know anything about it.
No luck on the NCI website. Thanks for mentioning it though.
So with that said, are there any professionals out there who serve the Cedar Rapids, Iowa area?
Any by pro, I mean someone that will do a manual J and D.
What's your zipcode and city/state?
you really need a Pro,to resolve the issues.
Ther is Profesional Design available on the web,might try to google it,not sure where but I've seen it.
I think there is some confusion about who is considerd a "pro" and who is not.
HVAC installer - A green rookie that is just starting out and does hard hot work that old fat guys can't do anymore. Some are stuck in this position due to their criminal background and/or drug & alcohol addictions.
HVAC Technician - An employee; a person that can accurately diagnose hvac failures and repair them correctly (within reason).
HVAC Design professional - A real book smart dude that can work up numbers on paper and tell someone else how to build a hvac system. In some extreme cases they even have college degrees in Engineering.
HVAC Guru - A guy that uses the correct formal calculations to aid him in prescribing a comfort solution based mainly on his years of experience and competence proven through examination.
Homeowners seem to think just because they called a "company" they should be getting the guru. Guess what cheapskates you get what you pay for and good design work isn't cheap. Now start asking for credentials of a person and not a company and be willing to PAY for their hours of design work and experience, more than just a standard service call. I am talking about severl hunderd dollars for a good road map to guide most anyone through the installation process. I mean why would a guru want to spend hours telling you how to install your own system or let some other company use your design for free. Now get off the bucks and quit whinning about not being able to find a guru. They are out there I promise.
"And remember my sentimental friend......that a heart is not judged by how much you love, but by how much you are loved by others" - Wizard of Oz.
You probably mean "get out the bucks"--I don't ride too many bucks.
I'm willing to pay for quality. The problem is, with all these guys undercutting each other, the quality guys are hard to find. As I said, I don't think most people even think much about their HVAC. Most people probably wouldn't even complain about the things I'm complaining about, but I'm a bit of a perfectionist.
I'm willing to pay a couple hundred bucks to have a good system mapped out for me, but whose to say they won't just b/s me anyway? They could tell me that they performed the load calcs according to Manual J and the duct design according to Manual D, but how would I know they really did?
You see what I'm getting at? Any schlop can put together some papers and show them to someone and say here are the results of your calc. I've said before, I'm uneducated in this area, so I'm trying to pick a few things up so that I can tell if the wool is being pulled over my eyes.
Until that time, I'll keep my "bucks" in my pocket and hope for some more constructive feedback.
Oh, my zip is 52401. Thanks.