Hello All,
I have a Ruud Achiever 90+ condensing furnace. I know that it was not installed by a ‘real’ HVAC person and I think the ducting is done really poorly and I think that I want to redo it myself hopefully intelligently.
Now before y’all say hire a pro let me relate a little story about why I want to do it myself. It was winter and COLD here (30degF at night cold for Oakland CA) and our furnace quite working. I was away at work and in a panic SWMBO called the first four guys out of the phonebook with the fanciest ads that said they work on RUUDs-a lot of them didn’t. They all came out and poked around for a bit and proclaimed that the most expensive repair possible was needed-replacing the ‘motherboard’. To a tune of like $600-$800 bucks! Yikes! She was not willing to authorize that without having me look at it. I get home from work and take out my volt meter, look at the diagram-flowchart on the inside of the furnace and start checking things. After about ten minutes I have it narrowed down to either the motherboard or this pressure sensor. I take a closer look at the pressure sensor and one of the connections is not on. It looks like its on, its pushed into place like its on-like someone wanted me to think it was connected but it wasn’t. After reconnecting the pressure switch bam it fired right up and I’m a hero!!! I surmised that maybe by vibration the connection worked its way loose over time originally and that stopped the furnace from firing. The connection did not reconnect itself just so though. So either the first guy was a crook or incompetent and all the rest of them were just plain ole incompetent and or they were crooks also. That’s why I don’t want to use a pro on the ducting as I am sour on the lot of them.
I have searched the forums and I think I know that the ducting is bassakward. The house is ~1200 sq ft being a two story with the heater on the ground floor and the ducting running in the ceiling of the first floor. The house is only finished on the second level so all the ducting is pretty much exposed and easy to get to. Heres what seems screwy to me; All the ducting is run in the flex stuff from the heater all the way to the rooms. There really are no main lines its run home-run style. The diameter of the ducting is the same no matter what the size of the room its going to. Our little master bath gets just as much air as our master bedroom.
What I want to do is rip out all the flex stuff and install a rigid system with intelligently designed lines. We are hoping to finish in a ~300 sq ft room with bath on the ground floor this summer and I am hoping that by redesigning the ducting that I should be able to heat this additional space with the same furnace.
The RUUD did not come with any doc-specs and I am tracking down its capabilities on the web-its serial number should tell me all I need to know. Once I get the specs I believe that with this computer program someone talked about in an earlier thread HVAC-Calc I should be able to design the ductwork correctly.
Am I way off base here with trying to do this myself? Does the ducting sound like its done really badly? Why are there no HVAC books for the diyer?
Daniel Neuman
Oakland CA
Crazy Home Owner
Replies
You do not give any info as to; What sizes are the runs?
What is the input/output Btu rating of the unit?
What distance is the furthest run from the unit?
Size of plenums (return and supply)
Proper sizing should be done via manual J, which takes into consideration of the amount of windows, insulation, delta T,etc.
Post back with some added info and we might just be able to advise you somewhat in order for you to eliminate taking a 1 year course on duct sizing and design.
Hi Hube,
I'm working on getting y'all some more details. There is this little thing I forgot about this year called....taxes...yep I have been scrambling to do those but this weekend I should have time to measure the ducts and such maybe even make a sketch of the system to show you.
thanks for the reply
Daniel Neuman
Oakland CA
Crazy Home Owner
Okay I did my measuring and checking. The furnance is a Ruud achiever 90 Plus with a heating cap of 56,000 BTU/Hr. I will explain the ducting next but this isnt going to be easy.
Intake: this is easy. Single intake of 16" diameter flex duct thats 22 feet long has 2 right angles its intake reg is 24"by14"
Blower side: Starts with a 12" dia flex duct 4' long to a 12"by10"by10" T. One branch of this T head towards the back of the house and the other towards the front.
Back T: 21' of 10" flex 3 right angles to a 10"by6"by6" Wye. One branch of the wye is 8' of 6" to a 4"by10" reg into bath of 45 sq ft. 2nd branch is 11' of 6" flex to a 4by14" reg into a 280 sq ft room
Front T: after about 2' there is a 10"by6"by10" Wye. This 6" branch runs 10' into a 4by12" reg into a 250 sq ft room. From wye the 10" branch runs another 8' to another 10"by6"by10" Wye. This 6" flex line runs 12' to a 4by12"reg in a 180 sq ft room. There is 8' more of this 10" flex line that ends in a 10by6by6" wye. One of these 6" flex lines runs 5' to a 6by12" reg in a 161 sq ft room. The other 6" branch line runs 14' into a 4by10" reg in a 180 sq ft room. All ceiling heights in above are 10'.
Crud that was a lot. I want to add another 250 sq ft bedroom and 60 sq ft bath that I would like to heat with this same unit.
How's that for info overload?
Daniel Neuman
Oakland CA
Crazy Home Owner
Finding a good HVAC contractor on short notice is tough. I've had similar experiences with incompetent techs who only know enough to replace parts. One guy replaced a relay board on a heat pump control four times (under warranty) until I finally got angry and told his boss to send out somebody who knew what the hell they were doing. They sent an older, experienced tech and he found the real problem, a shorted cable, in less than half an hour.
If you haven't already been there, take a look at this site:
http://hvac-talk.com/vbb/index.php
The regulars there tend to be "industry focused" so as a DIY, you are better off keeping a low profile unless you like being flamed, tared, and feathered ;-)
This software will allow you to run a load analysis on your house and size ducts. For $50, you can use it up to 60 days:
http://www.hvaccomputer.com/
It's no substitute for experience, but it can point you in the right direction and show where the previous "experts" may have missed the ball. Good luck on your project.
Edited 4/14/2005 11:02 pm ET by TJK
almost all of the new homes here run flex duct, i'm not crazy about it but it's much better than it used to be.you might look at putting dampers at the furnace takeoff and balancing the air that way.on my house i did hard duct,not rocket science, we have a supplier here called lockes supply and i could go in and browse there inventory and find things i didn't even no existed. larry
hand me the chainsaw, i need to trim the casing just a hair.
Here's my experience - don't know if helps you. I added about 650 Sq Ft
addition to a 1,200 Sq Ft house. I was told existing gas furn. had enough btu's left to heat new area. The way it was original was about 15 ' of 8x22 rectangular duct in crawl space that ended with a flat rectangular end cap. They just cut about 5 holes near the end and cramed 6" round duct to form an "octopus" of round arms supplying 3 bedrooms & bath. The 6" round weren't even attached with anything other than craming them into the holes. We ended up taking all sheet metal outside spliting seems open with chissels & pliers. Cleaned 50 years of filth out with Ajax and green sponge pads. Hammerd it back together and re-installed with good tape. I had a fittimg made to cap rect. duct and convert to 12" round metal. Ran about 5-10' of that and then stepped down to 10" round metal and then went about 5-10' before converting that into 8" flex wich then split into 4 supply for newly added construction.
Cleaning old duct was a lot of work but the old metal wasn't rusty and was higher quality than new metal. Total cost of new ductwork maybe $500. + lots of time in crawl space.
Is it the Ideal situation? Probably far from it. Is it 1000% better than what was there before? Absolutely.
Can't imagine what would have cost to hire it out. On my own similar size house I got estimates on gas furn. and ductwork install from low of $3,500 to as high as $8,000.
Who's to say they'll do any better job than you can do yourself? My guess is probably 1/2 know what they're doing??? I've always been told that most installs put in larger than needed units because people complain if thay put in "correct" size efficiant units. I think the deal is that it takes forever for house to heat up and runs all time at lower temp. and people percieve it not to be working right?
If you contact 2 or 3 hvac 'specialists and get some proper input on a well designed duct system you can then rest assured it will be installed to obtain the best results possible.
Many,many homeowners (diyers) create their own problems by 'monkeying' with technical issues that they know very little about. And then complain ever after.
This is why most building trades have 4 or 5 year apprenticeships and several schooling courses. This can be in the range of 10,000 hours of training.
Hi Hube,
I agree that this would be the best way to go but do you know any real knoweldgeable HVAC specialists in my area? I sure don't and I don't even have any leads on one.
What I don't mind doing is paying someone who does know their job to come out do all the figuring and planning then handing me the plan and I do the dirty work. I use a pro they get paid they don't have to do any of the crappy work and I save some money, should work out great for both of us right?....just gotta find that pro.
Actually I feel that I should be completely capable of designing my own ductwork given the right references. I understand the physics behind it all I believe (I am a madscientist after all).Daniel Neuman
Oakland CA
Crazy Home Owner
I think that most HVAC shops have office personnel figure out the trunk and branch sizes for ductwork installations.A lot of the tinners that I work with on commercial jobs can use a ductalator,but figuring out the needed cfms for a given space and determining blower sizes is beyond them.
I sized my equipment and ductwork using the software for sale at the HVAC Talk site.You pay them $50 and download the program which enables you to do a load calculation for your house.It also gives you a CFM report for each room,and then you can use the duct sizing portion of the program to establish trunk and branch sizes.It isn't perfect because it can't anticipate the lengths of runs and number of fittings for a particular installation.It also doesn't take into consideration what kind of duct parts are actually available.A small bathroom might call for a 3" branch duct,but nobody sells a 2 1/4" x 12" x 3" boot.I actually found another article on the net that has rules of thumb for duct sizing which was just as close.
It's ironic that the HVAC-Talk site owners sell this software and then crucify anyone they deem to be a DIY'er.
"It also doesn't take into consideration what kind of duct parts are actually available.A small bathroom might call for a 3" branch duct,but nobody sells a 2 1/4" x 12" x 3" boot."
I know from reading your posts over the last few years (and the brotherhood handle) that you have a practical working (or greater) knowledge of the electrical trade. The sparky equivalent of a 3" supply duct would be a 5A branch circuit. I have never seen a 5 amp breaker. A 10a is the equiv of a 4" duct (i.e. almost useless as a supply) but does have its application. You can, BTW buy a 2-1/4"x10"x4" boot. A 2 1/4" x 12" floor register should to be used for 50 to 70 cfm supply, which would require a minimum 5" or better yet, a 6" branch duct.
This is why I suggested the HO/DIY look at a catalog of standard fittings and use that info as a starting point when determing the layout.
"Am I way off base here with trying to do this myself? Does the ducting sound like its done really badly? Why are there no HVAC books for the diyer?"
You are not way off base, an all flex system is done poorly. Why are there no DIY manuals? I don't know. I think I might write one!
With a little reasearch, you can do a lot better. Find a supply house or manufacturers' rep or somehow get a hold of a "ductulator". Try finding an "Air Cold Supply" in your area.
Look at a duct supplier like http://www.southwarkmetal.com/pdfs/wc_sw.pdf to see what commonly available pieces and parts are out there. Google and see what esle you can find.
Although not the most scientific or complete way to do this, a STARTING place for ducting your house is to the following; determine the cooling air flow of the system. The cooling airflow is the nominal tonnage of the air conditioning unit x 400 or the btu rating of the AC / 30. Size the duct(s) going to each room to account for 0.5 to 1.0 cfm/ft2 or the ratio the room/house x cfm for the system.
Draw a diagram of how you plan to run the duct showing truns and offsets, branches and registers, etc. Label it with air flows and then determine the sizes of duct that you need. One hint is to plan on using 6" branches going to most registes to keep the takeoffs, elbows and boots consistent. You can approximate the need by assumng 100 cfm, per 6" branch and fro each 4x12 register. Use standard trunk sizes which are 5 FT long x 8" deep and come in widths of 24, 22, 20, 18, 16, 14, 12, 10 & 8". Buy 30 GA or STD GA, when you have a choice.
Get some good tools, Wiss snips in a couple different varieties, a good magnetic 1/4 nut driver attachment for the cordless drill and some #7 x1/2 sabre point screws. Get some good fitting leather gloves and use the religiously or you will bleed. Some good foil tape is recommended, though not necessary.
Sheet metal work is tedious and takes some getting used to, to get a system down. DO NOT SKIMP ON THE TOOLS OR SCREWS. Plan it out right and take your time. It's as easy as sweating copper pipe.
Can I ask some CAC questions:- So if you had your house retrofitted with CAC, not realizing they were going to put in flex everywhere, is there anything wrong with replacing flex where I can with solid (for the higher efficiency of air transmission), replacing X" flex with X" solid?- I had them put ducts in the attic under the floorboards instead of overhead, figuring I'd dump insulation on top of them when I got around to this (again, not realizing I was going to have flex ducts). Is it a bad idea to dump SPF and say 1' of cells on flex ducts? The original idea was not to have R49 attic insulation and then R6 ducts carrying house air through the attic....- Installers will have to come back and rerun flex to kitchen, since I moved a plumbing wall in the bathroom that it went through. They will probably squeeze 8" flex through 3" gap between top plates and down the stud bay to a similar gap between bottom plates. How much efficiency am I losing by having them doing this? They clearly think there is nothing wrong with squeezing the flex duct through tight corners. And is there any kind of solid ducting I could put in there myself, to regain some efficiency? It's going to be a long run because I'm going to ask them to then run the duct to the other end of a kitchen soffit so the vent isn't right over the stove (fire worries).This does make me wonder if I should have opted for Spacepak or Unico, but every installer I spoke to told me it was unnecessary.
"...is there anything wrong with replacing flex where I can with solid (for the higher efficiency of air transmission), replacing X" flex with X" solid?"
No, there is absolutely nothing wrong with replace flex with gavanized duct. It would be very hard (though possible) to create more resistance to flow. However, this may or may not improve the overall operation of the system.
"Is it a bad idea to dump SPF and say 1' of cells on flex ducts? " No, not a bad idea at all.
"They will probably squeeze 8" flex through 3" gap between top plates and down the stud bay to a similar gap between bottom plates. How much efficiency am I losing by having them doing this? An 8" round duct is good for 160 - 200 cfm, a 2x4 stud bay w/ a 3-1/4x14 wall stack is good for 120 - 150 cfm.
A hack could have installed the Unico/Spacepak, but these systems are designed for hacks. Unnecessarily expensive, but almost hack proof.