diy furnace install - a/c question

darrenwOctober 1, 2006

(apologies if this was posted twice..was having some posting problems).

First off, If I was able to find an installer that gave me a reasonable price AND could fit me in, I wouldn't be doing this myself (the one guy I found that gave me a reasonable price was too busy..go figure).

I plan on have a technician come and service the unit and check my work before I turn the gas on....

My 20 year old Rheem has given out, and I'm replacing it with a Goodman upflow. Trouble is, my York A/C Case dimensions are 20" x 21.5", but the top of the furnace, measuring from tab to tab, is 23" by 20.25" The furnace will extend out about 3" in one dimension...this seems excessive to me.

My question is: What is the "right" thing to do in this situation? I pulled a permit and want to be sure I do this right.

Thanks in advance.

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Hope you had a heat gain/loss calculation done on your home first. Reason a newer furnace puts more heat (btus) into the ductwork than older furnaces with draft diverters. The furnace may be oversized and will burn more fuel than a properly sized one. The same with the air conditioning. Don't go by some BIG BOX square footage recommendations for sizing as they can be way off as well. Two homes side by side with the eact same square footage will have different heat loss/gain depending upon roof color amount of insulation in walls and ceiling. Types windows and doors.

    Bookmark   October 1, 2006 at 7:53AM
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Many manufacturers have an overhang on the coil. Usually it is to the rear of the furnace. Do not be overly concerned with this. Make sure the air path is smooth and does not have a sharp change in direction.(No stair steps)

Other than this problem, is everything installing similar to the previous unit?

When connecting the gas, use a thread dope or tape to seal the threads. Most units are so simple to fireup. The tech does very little. The problems are usually on the AC side. If the Gas is real yellow, it needs adjustment. Otherwise the most important issue is gas leaks. Sometimes The gas has too much pressure and this causes

Set the fan speed correctly for AC.

    Bookmark   October 1, 2006 at 11:19AM
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mechacc1 and bob_brown,
Thanks for the responses.
Mechacc1: Heat/Gain loss calcuation came out to 90,000. I went with a two-stage, variable speed, 80,000/115,000. The house is three levels with varying temperature differences on each level, and lots of windows...came to this decision on my own, as well as what was recommended by the estimates I got from installers. I figured for Colorado climate, this made sense.

Bob: Not sure I totally understand your response: The furnace is overhanging the AC, not the other way around. my concern is the right way to seal that off so the upward flow isn't getting turgid right out the box...if it was the other way around, I wouldn't be as concerned. Since the AC coil has to sit directly on top of the furnace (right?), there would be up to 3" where the air is pushing up outside the AC box....I could just cover that with sheet metal and foil tape, but is that the right thing to do? This might seem really obvious, but since I'm a novice, don't want to do anything stoopid.

Thanks for the suggestions on the the AC. I will get help with that.

Otherwise, I need a new return air duct, and need to carefully figure out my vent hole(it's a 95% AFUE..old was an inefficient 125k BTU unit) so I don't screw up the slope, and probably will need to drop a flue liner in my old a litte bit of work, but everything else makes complete sense ( far).


    Bookmark   October 1, 2006 at 12:16PM
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daren you do know that has to be vented outside........

and on a pitch.

insead of covering it with sheet metal could you make a small transition. (maybe you can't but a loval sheetmetal place can) make it look professional. then get duct cauck and that should do the trick as far as leaks, also make sure you leak test the gas pipe with soap and water.

    Bookmark   October 1, 2006 at 3:04PM
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Yes..1/4" per foot. Just punched the hole through the outside of my house. The instructions say 2" or 3"..does it matter, or can I step down from the 3" out of the furnace to make the hole that much smaller?

The transition makes sense, but if I do the transition, what is going to support the AC Coil? When you say loval sheetmetal, do you mean foldover the sheetmetal, or stack it somehow? I know this is basic, but still not picturing how the AC is going to be supported.

Will be definitely testing for bubbles... No interest in blowing up my house.


    Bookmark   October 1, 2006 at 3:13PM
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sheet metal should be made by a sheet metal fabrication place, spend the 50 bucks to make it look good. bring them the measuremeats and if there good people they will show you an example that might be in the shop. i am thinking of maybe using a 20 guage steal. they know what there doing and it will be rather solid to hold the weight of the coil no problem......... but defintly go to a fabrication place and have them fabricate the sheetmetal for ya. while your at it ask them what a flex connector is so you don't ask later if you have a tight spot.......... maybe 18 guage too. it been a while since i hade to do that.

    Bookmark   October 1, 2006 at 5:19PM
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Thanks much..that's a great suggestion. Will see who I can find in the area.

    Bookmark   October 1, 2006 at 6:59PM
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I am in upstate NY. Installing goodman 2 stage, variable speed GVS 70K unit ($1k delivered). Contractors wants total $3800 for a one day labor. I am an elect engineer and looks poor ($40/hr) in front of this tech ($250/hr)! I know electronics, motor drives and gas fire controls. I may need help for the old gas pipe removal (hard to disconnect old rusted pipes. That is the real challenge). sheet metal work will be done by the pro.
I would keep informed as I progress and my learning experience.
Please let us know your experience and advice on your DIY furnace installation project.

    Bookmark   October 19, 2006 at 11:39PM
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Ummmm...where in upstate Buffalo the job could have been completed for about $2,500 - $2,800. I'm wondering if there wasn't far more involved as far materials (new drop, chimney liner, gassing, hardwired smoke detection, thermostat, etc.). Did you get more than one quote? Keep in mind the tech isn't making that money...there is work comp, permits, insurance, van payments, etc. At the end of the day they will be getting less that your $40 an hour! Good luck and good health.

    Bookmark   October 23, 2006 at 12:25AM
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Finally done -
Installed 70K two stage, variable speed Goodman furnace!
Cost: $1070 delivered + $65 plenum sheet metal shop + @100 extra. +$200 plumber + My time.
This plumber help was arranged by my friend. He installs furnace for Sears and other big business. Now I learned the inside story of the furnace business. He gets about $500 to $700 from Furnace Dealers to install furnace. Dealers salesman gets about $200 plus other kickback from the dealer. Company get remaining cream. But in return, company pays for the liability insurance plus warranty handling expenses! Parts warranties are covered by manufacturer but processing and handling can be a cost but not much.
Now my installation experience:
Plumber was a strong guy. He removed old GE furnace quickly and put in his truck for scrap dealer!
We both place new furnace like a gas dryer! Plumbing went smooth. Installed black pipe and union to the gas valve and install new semi flexible stainless steel pipe to main via gas valve and dirt trap T.
I had finished all electrical connections and we both fired furnace. Came up fine, let it run about 30 sec interval at a time (without blower kick in) to let burn oil deposits. Tested all joints for leaks.
There after we started furnace and let it run for 5 min. I turned down Low and Hi adjustment screw (on gas valve) to half turn down to reduce pressure.
Now furnace is working fine, kicks in second stage after 10 min only in real cold weather or when I boost my thermostat two degree up.
Main installation time about 3 hrs. My pre and post prep time about 8 to 10 hrs which includes my exhaust and inlet pipes installations.
I know electrical, controls and thermal engineering. Even plumber enjoyed my technical knowledge. We both exchanged our technical know how. He had his experience and I had my theories!
Warranty Issue: If you ask HVAC dealer then they will tell you all horror stories! This is normal scam because this is brings a fat profit on fear! HVAC equipments Manufacturers are legally bind "not to tell" or promote DYI with their regional distributors! I think recently Goodman has open up that channel and may take advantage! I do not think furnace installation is too complex but need technical aptitude and some help from plumbing or HVAC tech.
By my recent experience and electrical engineering know-how I would recomend to buy Goodman GMH series (simpler and cheaper). it has multi-speed motor in place of variable speed motor (GMV motor has a complex design and expensive to replace).

    Bookmark   December 6, 2006 at 1:33PM
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I bought a used gas furnace and airconditioning system from a guy at work for $500 and installed them myself including building a new plenum and replacing about half the ductwork. I also installed a new gas furnace in a rental house I own. I had never done any of this work before. They are both working fine. The trick to saving money is to trick the wholesale suppliers into selling you the furnace and parts at the contractors price. I paid a contractor $50 to call in the order for the new furnace and say he would send someone down to pick it up will call (that was me). That saved me several hundered dollars. The only thing I had to hire a pro for was to vacuum pump the airconditioner and then charge it with freon, which some moonlighter did for $50 plus cost of the freon. The markup between contractor prices and retail is unbelievable. But now some of the big box building supply stores are selling stuff like flex ducting so now there are alternate sources for the DIY. I ran all the copper lines myself and also did the elecrical work myself, including running conduit.

    Bookmark   December 24, 2006 at 2:53AM
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The biggest difference between the word profwessional and amature is money. One gets paid, and the other pays the money. At full dollar, you are still saving a lot of money.

In the N. Texas area, I know of one licensed HVAC installer that works for multiple companies installing HVAC. He perfers to only do condensers. A typical job costs about $150, including parts labor and taxes. I did not use the guy, but a guy I worked for did. He used my license to buy gas. He sold replacement hvac systems, without a license. He was a hack that had customers. A typical contractor spends about $500 per year for insurance, and another $600 for city/state licenses. If he contracts in one city the cost can be less than $100 for licenses. If he does as few as 20 units the cost is defrayed to $55 per unit. But he has to have the insurance to be legal and do service, so the cost of installing a system is not so expensive.

As a contractor, he knows where to buy materials, and what to do, so he should always spend less money than a consumer.

    Bookmark   December 24, 2006 at 4:10PM
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I agree with you. Licensing, insurance and permits are the major cost for the professionals. But on other hand these professionals love such govt rules! On many cases, these professional organizations bribe local politicians and promotes such licensing process to develop monopoly in that area. Particularly, plumbing, electrical and home building organizations are the major contributors! I know in my nearest town limit, home owner can not replace simple electric switch without licensed electrician or solder copper pipe even though home owner is an experienced engineer!
I am not against unions or business organizations but I think some time they abuse their powers to rip-off naive customers.
In many part of the NJ, home owner needs permit to replace their heating furnace and they have made the process so complex that most of the time home owner prefers to hire contractors! Even local utility company provides that service with hefty charges! Last summer, my friend in NJ paid more than $8K to replace his 60K BTU furnace and AC unit for 1600Sf home! He told me that was the best deal he got! Actually many contractors asked for more than $10K and more than month of time to finish simple job!

    Bookmark   January 26, 2007 at 5:44PM
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Wow, you turned back the Low and High adjustment screws one-half turn after the furnace ran for 5 minutes.

I'll bet you had your finger on the gas line going to the burners so you could get an exact measurement on the supply pressure to the burners.

My fingers aren't that sensitive, probably because I am not in touch with my feminine side and therefore not as sensitive to gas pressure outputs as you seem to be.

I always have to use a manometer to set the gas pressure.

Would you be so kind as to supply me with your legal name, address, and heirs names?

I get the distinct feeling that it would pay me great dividends to buy life insurance policies on you and yours and I won't have to wait long to collect on those policies.

Ah, Darwinism can pay better returns than the race tracks.

Hiya Baymee, MrHvac, and Rabadger.

Fairy Princess

    Bookmark   January 27, 2007 at 3:24AM
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Last year with the new 13 SEER regulations, many contractors raped the consumer. Jobs that previously cost $3500, were quoted for $12,000. It didn't make sense, but with the confusion of the new regulations (new rating methods delineated the actual cooling capacity but allowed the maximum theoretical rating to remain) the typical contractor made up his own rules. Many stories of $500-700 condenser fan motors. A motor that cost less than $75 and takes about 30 minutes to replace. Even the honest guys were overcharging the customers.

This forum and other forums attitudes towards new equipment started with stupid beliefs. It took most of the year to change opinions. Trying to explain SEER and what it means is impossible. Just smoke a few more cigerettes to reduce cancer odds. OR smoke dope and forget everything.

    Bookmark   January 27, 2007 at 12:33PM
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Good post fairy princess, hey can I get in on that insurance benefactor thing too? :-)

    Bookmark   January 27, 2007 at 3:44PM
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fairyprincess -
Man, are you sane? This is a DIY forum to share technical information, not to criticize anyone! If you have manometer then it is good but it is not required if I know what I am doing! I was not raising gas pressure and I am an experienced engineer and I know what I can and can not do!

    Bookmark   January 28, 2007 at 8:55PM
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First off, you DO NOT know what you are doing as far as setting gas pressure to the burners goes.

Secondly, you are so full of yourself which makes me suspect your engineering degree is very old and you are living on a false undeserved ego, or you are an engineering student who just got into the classes and feel you have earned the right to the title.

Instead of a rebuttal telling me what the gas pressure is coming in to the gas valve and the pressure that is supposed to be coming out of it to the burners (It's in the installers manual that should have come with your new furnace.), you throw around your sheepskin like so much toilet paper.

I am not critizing you as I sincerely would like your and your families legal names and particulars so that I can make some insurance money on your respective demises.

Sounds more to me that you are doing deep knee bends in a cucumber patch while completely naked to make yourself feel good about a degree which you have shown is completely worthless in this particular DIY procedure with the furnace install.

I have no objection to you hurting or killing yourself with your misplaced, undeserved, overblown ego, but think of the family and friends you may end up taking with you when the excrement hits the oscillating blade.

Open your bulging wallet (If you really are a degreed engineer, it will have money in it.) and hire someone who has the equipment and the knowledge to set the furnace up correctly.

You guys who think you can figure out, or know it all really irritate those of us who do know proper procedure.

Fairy Princess

    Bookmark   January 28, 2007 at 9:33PM
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Whoa fairy princess! I thought I was venomous! My hat is off to you and you have my utmost respect. If this BK(which I think stands for Burger King)is really an engineer then he has an excuse for being such a dang fool. You know those engineer types, everything always fits in the space and works IN THEIR DRAWINGS!

    Bookmark   January 28, 2007 at 10:06PM
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Hey Mr. Hvac:

I'm not going to let you off so easy just because of this simple compliment.

I'm still a little upset with your "rude" remark because you think I'm living off the dole with my bad knees.

Thanks for the compliment anyway, but Bk2000ext sounds like he needs a serious reality check in this particular instance.

Fairy Princess

    Bookmark   January 28, 2007 at 10:42PM
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OK..Pal.. Now I have about 4 months with new furnace.
According to my one winter experience I would recommend GOODMAN variable speed, 2 stage furnace. Last NE winter month (Feb), outside temperature stayed about 10-15F day and below zero at night with wind-chill close to -20F to -30F. I hardly felt winter inside my home. I set my thermostat close to 67F, furnace kicked every 20 to 30Min for 8Min, and we were comfortable. My gas usage went down 25 to 28%.
Furnace is running fine and did not cause any trouble.

If you buy this furnace then do not forget to buy or build an external filter side rack (unless you setup bottom air intake).

    Bookmark   March 8, 2007 at 7:47PM
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If you need a manometer, You can improvise with a 5 ft length of tyvex clear hose. Make a 12-20 inch loop and fill with water. Tape it to the side of the furnace. Use a marker and draw a line where the 2 collums meet. Connect it to a straw and insert into the air flow for static pressure. Use a hose barb and connect the hose to the test port on the valve for gas pressure, measure the difference between the 2 collums of water and divide by 2. This is inches of water collum. Home Depot sells a kit that does the same thing. It is called a water level. Most gas valves can be adjusted to water. Some are rated in mercury. There is a math conversion. I used a 4-collum mercury manometer that I had for adjusting multiple carbs, in the beginning.

I used the same principal to level a house. I used a 50 ft tube. After 2 years, 2 of 18 piers were off by 1/4 inch. Typical leveling is done to 1/2 inch accuracy.

    Bookmark   March 9, 2007 at 12:30AM
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"If you need a manometer, You can improvise with a 5 ft length of tyvex clear hose. Make a 12-20 inch loop and fill with water."

That is the hard way for small pressures.
Just submerge the end of the hose in a bucket of water til the bubbling barely stops, then measure how deep the hose is from the surface of the water.

    Bookmark   March 9, 2007 at 9:40PM
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Bob Brown and Brickeye:

Come on now, if he listens to you guys they might throw his prissy butt out of NOW and cancel his subscription to Cosmopolitan.

He probably has much more faith in letting it run for five minutes and then backing off the the Low and High adjustment, whatever that means.

Bk2000ext is so off his game that he has to come back on here a little more than one month later thinking he is going to get a little more respect for his insane installation just by showing us he is still alive and the install is supposedly working the way he thinks is right.

Bk2000ext; get a grip and hire someone to set the furnace up correctly before people close to you die.

My insurance agent tells me I can buy a life insurance policy on you if I use part of the proceeds to advertise and advise on the unsafe practices used by some DIY types like yourself regarding furnace installs.


    Bookmark   March 12, 2007 at 1:04AM
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Wow, Fairy princess,

You are disrespectful and, as my southern friends would say, hateful. C'mon guys, you have got so wound up about this guy being an engineer you are forgetting that you use a similar lame tactic when you are selling your own services. `Licensed technician' ... Oh, please. It takes TONS more perseverance and dedication to get even the most basic engineering degree than to get, say `EPA certified' (which can be done without preparation with just a solid knowledge of high-school physics). And yes, your darn unions do skew the odds in your favor (I am yet to see an `engineering union', oh yeah, because they teach you in college that it is unethical) and you do use scare tactics on customers (most of you any way). Have some respect for this guy's expertise, as well. If his engineering degree is old, even more so---it used to matter more those days. And what, you, licensed professionals, never do a shoddy, dangerous job? Sure you do, with all the bs you poor on us. If you want to give a technical answer, or simply say, `You have to use a manometer for that', then do so, but do not hide under your `technician's license' or 30 yrs of experience (which under different circumstances would be a reason to listen) to obscure things even more. Because of contractors' attitude, there is hardly any information on the net about HVAC installation but fortunately, it is still legal to read library books. Want to keep this knowledge to yourself---do not post but if you want to help---answer the question that was asked. After all, he did not ask you any electrical questions, probably because he knows far more about it then you average hvac tech. Cheers.

    Bookmark   July 10, 2007 at 3:52PM
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I did a DIY install on my 60K/90K Goodman last fall and used it all through the winter - I had to convert mine from natural gas to propane as well, but that didn't seem too difficult to me. It worked just fine all winter - Nice looking flame tips in both first and second stage operation. Carefully checked every joint for leaks. Hope my house doesn't burn down or blow up . . . . this is really technical stuff here and I guess I should have had a degreed engineer looking over my shoulder

My background is also in electronics and I don't have a manometer either . . . . maybe I better get more insurance. I WAS prepared to have my local HVAC guy come by with his and make the final adjustments, but when he came to charge my A/C system this spring (also a DIY install) he checked my furnace (visually) and said everything looked fine, so he didn't bother getting the manometer out of the truck

If/when I do get more insurance, I'll look for a more civil, friendly type to leave it to than some of you guys!

There is an unusual group who hang out in this forum. About 75% of us are amateurs, seeking advice on how to do a proper job doing things ourselves. You would think the remaining 25% who do profess to be 'professionals' would be a great asset to us all, but all most of them seem able to post is that the rest of us are idiots for wanting to do it ourselves as opposed to paying the $100 to $150 per hour they think we should pay them. Sad part is, many times when you do pay that kind of money you still get a piss poor installation and you would have been better off and safer too if you had just done it yourself


    Bookmark   July 10, 2007 at 4:23PM
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I hate to be trolling in this forum but while I was trying to gather bits and pieces of information on diy AC installation I came across an interesting thread in this very forum:

`Mr. HAVAC - one for the books'

Very enlightening to see what the self-professed `true-tech' or `professional' attitude amounts to. One guy almost burns down a customer's house and is proud to have kept him looking the other way while his assistant was frantically putting out a fire (resulted from heating the liquid coolant line with a torch---a procedure explicitly prohibited by EPA, OSHA and a dozen of other agencies; comes up on 608 certification test, as well). Nice way to instill confidence in us, amateurs.

And thanks a lot for the post, Don. At least I know it can be done, maybe someday someone will post pictures of the whole process, as well. Cheers

    Bookmark   July 12, 2007 at 3:54PM
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We had a home warranty policy that replaced an old Lenox pulse furnace. (we have 2 and only 1 needed replacing). The problem was the "professional" installer the insurance company had install the new unit. The installer used the old PVC muffler from the pulse and rigged up to the new unit (for the out take air only) the intake air pvc vent was cut and left touching the unit. They did a total bogus job and to boot they didn't even pull a permit. Now we are looking to have this unit installed properly and the other replaced along with the ac unit. The cost $13,000. for everything. We are just sick. (we live in colorado)

    Bookmark   July 21, 2007 at 12:47PM
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What does your post have to do with the original title post of "DIY furnace install"?

    Bookmark   July 21, 2007 at 10:01PM
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Mr. HAVAC - one for the books'
tl nix, hey pal if you don't like my attitude keep this in mind, its a free forum, you get what you pay for. If you or anybody else would like me to share the knowledge and experience I've acquired in the last 30 years I'll sugar coat it as much as you like. But be prepared to shell out some bucks because I won't give it out for free. I won't mind calling myself a consultant and get paid accordingly. Have you noticed most knowledgeable professional contributors don't stick around here that long. I has alot to do with what some of you posters expect. Who needs that crap?!!! I'm just about done in here myself. If I want to perform a service I'll do it on the local level face to face. At least the people around here don't whine when they are getting a valuable service free of charge.

    Bookmark   July 22, 2007 at 12:07AM
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After wandering onto this site by accident, I have become more than a little amused. In particular, concerning the supposed low cost of operating a professional heating and air-conditioning company. I have firsthand knowledge of those costs.

My small business has 5 employees. In FY06, our cost of doing business was over $340,000.00. That includes wages, office and shop costs, insurance (liability, theft, workmans comp, health and auto), automotive maintenance and repair, employee retirement, tools, licensing and permits, etc. That does not include the actual cost of goods sold. Any profit that is earned beyond that amount is at least deserved.

Most companies extend a one year labor warranty on the equipment they install. If there is a warranty repair, they are not compensated by the manufacturer for their time. This is a cost of doing business that most people do not consider. If a thunderstorm comes by tonight, and knocks out a compressor, we will replace it tomorrow if the year warranty is still in effect. No, that shouldnÂt be covered but we are noted for going above and beyond. It has built an incredibly loyal customer base.

Three of our six vehicles are specialty utility vehicles. These are not inexpensive to purchase, operate, maintain or repair. Operation of these vehicles with gas prices at $2.50 a gallon average $.79 per mile.

I am certainly not complaining about my job or my business. I make a good living and very much enjoy what I do. However, since shots have been fired, I feel compelled to fire back.

Though we purposefully avoid dealing in equipment as low in quality as the unit described, I have read through a GMC 90+ Installation manual before. Reading the manufacturerÂs written instructions are not an option for this engineer. Whoever heard of an engineer that did not read the instructions? All furnace manufacturers are very specific about the installation of the exhaust vent. Regarding length, size, termination and even number of 90 and 45 degree turns allowed. Additionally on the vent, I have only seen long sweep elbows specified. The point of the exhaust vent termination is critical as are the instructions for preparing the termination area. If the directions are not followed regarding termination, you have a high probability of damaging your home.

As mentioned before, we do not install GMC equipment. However, I cannot remember reading any furnace installation instructions that did not specify using a manometer for checking and setting proper gas pressure/flow. The equipment we install is very specific about transitioning mismatched sizes of furnace and indoor coil.

It is obvious sir; you either did not understand or did not thoroughly read the instructions. My impression of an engineer that is earning in the mid 80Âs is they must be an underachieving, 9-5 cubicle dweller. I have been a registered PE since 1989. I think you must drive the choo choo. We are definitely not the same kind of engineer.

To my knowledge, all HVAC equipment manufacturers warranties are void if the equipment is not installed by a qualified, trained HVAC professional. Your plumber looking at it after the fact does not qualify. However, manufacturers are too lenient about warranties. They will probably give you the parts that might be destroyed due to improper gas flow or improper exhaust venting. However, if something serious happens, like burning down your home or soot damage, your insurance company will want a licensed insured company to sue. Since there is not one, they just will deny the claim.

My free advice here is to find an exceptionally qualified company to double check your installation. I am sure they will charge beyond what you think is "reasonable". However, you have stepped into an abyss that is beyond your comprehension.

    Bookmark   September 18, 2007 at 11:52AM
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I have a Goodman 2 stage furnace replacing an 20 year old unit. The old unit is 55" tall with the return duct entering the bottom left side, (14" X 20"). The new unit is 40" tall with a bottom knock out for return air. Does anyone know where I could get a kit for a plenum 15" high X 20"X 28" to attach to the bottom of the furnace?

    Bookmark   September 22, 2007 at 7:15PM
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Find a local duct fabricating shop. More then likely they will make up the fitting you need.

    Bookmark   September 22, 2007 at 9:05PM
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I had a furnace, 55" tall with a A frame coiling coil mounted on it. My new Goodman is 40" tall. Should I raise the furnace 15" and then raise the return by cutting off the 15" excess length or lower the cooling coil 15" and add a transition to the supply plenum? I would like to have the return enter from the bottom of the furnace, as the cutout is located there. How would I get the return to bend 90 degree and go under the furnace?

    Bookmark   September 27, 2007 at 9:52PM
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Just send one of the 'experts' here a couple hundred dollars and I'm sure they will help you out - They hate to see you doing anything without them getting paid . . . . the only reason they hang out here is to belittle the efforts of all the DIYers

All you're likely to get in the meantime is their assurance that you're screwing up and going to burn your house down


    Bookmark   September 28, 2007 at 11:21PM
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LOL you dont have to send the so called experts nothing. I wrote a guide for DIYers to help with installing a furnace (contractor for 20 years installed thousands of furnaces)

Its pretty simple. The guide can be found at

PS two more months and there will be a guide for installing boilers and AC's.

There is also free repair guides on the site. The best one being for boilers, and there is a how to solder pipe tutorial there.

    Bookmark   December 9, 2008 at 9:47AM
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This is for englewood1 ,, you dont have to return in the bottom . You can simply cut a hole in the side of the furnace and use that for a return, and leave the plate in place on the bottom of the furnace.

cheers tony

    Bookmark   December 9, 2008 at 10:07AM
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Call TDH Mechanical tomorrow and I will help you get through this. Ask for Tim

    Bookmark   July 20, 2011 at 1:43AM
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Just for all you wanting to do it yourselfers out there...
I installed two months ago a Goodman high efficiency furnace in my home by myself...and it was easier than I thought it would be. Goodman provides great detailed instructions, and lucky for me, there is a Goodman dealer about two blocks from my house. I pulled a permit and then ordered it online (way way cheaper) and it took about two days of work (for the furnace, no a/c) and some time researching and rounding up parts. I started by determining what size heater to buy, and my small energy efficient house needed less than the 46,000 btu Goodman offers, but that's as low as they go. I plan to heat my basement in the future so some extra capacity is ok. The existing cold air return was too small according to my math, so I ran flex duct, framed in, and sheetrocked a new return, which took about a day and a half. The rest of the duct work was sufficient. The flue and air inlet went together quickly aside from cutting the holes in the side of the house. I recently replumbed the house for natural gas, so hooking it up was quick. The duct work had to be custom made, so I had the local shop cut and bend flanges on a series of sheets. These I cut further, bent with a homemade brake, riveted and taped to create the inlet and outlet plenums. I added an outlet to my electrical box to run the condensate pump since I don't have a floor drain. Once the electrical and drain was hooked up, I tested the gas pressures with a homemade manometer as well as the static pressure of the unit. I also sampled the temperature rise as specified. Lastly, I called the local hvac shop to come service my furnace. They checked the gas pressures and confirmed they were within limits as well as the static pressure and duct sizing. The burners did not require adjustment. I had them check over the fresh air inlet and flue plumbing. They complimented the professional appearance of the plenums.
It can be done, and if you are capable of pvc plumbing, gas plumbing, basic 110v wiring, and very basic sheet metal forming, I would recommend you give it a try and have a professional check it out.It is important to take a methodical approach to get everything right...
quoted: $2500
actual cost: $1300 (including cold air return, framing, drywall, etc)
Good Luck!

    Bookmark   November 1, 2011 at 2:56AM
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