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Need ammo for contractor - replacing furnace


We recently did a gravity replacement in Indian Village in a home of about 3200 sq/ft. Heat loss came out to 89,700 btu's we installed a 92% 100,000 btu furnace. Now this is not to say that your home has similar construction properties but if a heat loss is not done you will never know. You can always do have the heat loss done yourself and insist on the proper size.

Supply duct risers within the walls are typically re-used. They are most likely double wall so the interior area is smaller than the exterior and they may not be too large. That would have to be determined by each rooms airflow requirements. Sealing the old duct, or replacing them would most likely be impossible without opening the walls for access.

Returns are required by code in all conditioned spaces except the kitchen and bathrooms. Sometimes this could be as simple as a transfer grill, undesirable and possibly ineffective but maybe acceptable, it would depend on the attitude of your local inspector. You could call him/her and ask what would be required. If you would like to learn more the following is a good resource.


It seems to me that the low interest loan may cost you much more over the long run if you have to put up with a shoddy installation.

Hope this helps,

John T.


  • John Bonetti
    John Bonetti Member Posts: 5
    Need better advice than I'm getting...

    I'm getting a loan through the county to replace a gravity furnace with a 80% effic. gas furnace. I had a "should I replace" post previously in this forum.. Anyway, the lowest bidder bid $3000 less than the rest of the contractors and I have to use him. He didn't visit us until after the job was assigned to him and now I feel he is not qualified and is trying to cut corners. He bid on the job sight unseen.

    The bid states he must "remove existing furnace and all duct work. Furnace must be sufficient BTU to properly heat house and operate at a min. 80 efficiency after installation. Install new and all necessary components and connections, new diverter grills on hot air ducts.... and proper asbestos removal". He did not do a heat loss study and is guessing that we need a 90,000 btu unit (which seems right to me). He also stated that it would be vented with pvc through the side wall (which didn't seem right to me - I thought an 80% furnace vent was too hot for that and needed to be ducted out the chimney..). We asked how much more it would cost to ensure that the furnace was big enough to heat an additional 300 sq feet (we may add a family room later). We also mentioned that we might want to add a/c at a later date and would like 3 registers in the basement that aren't currently there. He said that would cost an additional $1200 since we'd need a 120,000 btu furnace and he'd need to prep for future duct work etc. That seems very steep to me and I think he's trying to recoup some of his losses for an improper bid - and yes, I opened myself up for that one.

    He didn't want to touch the existing ducts in the walls and said that they would be fine. I'm sure that there are leaks - and the ducts are about 15"x3" rect. throughout. My research showed that at the very least, they should be sealed with mastic. I am also concerned about no 2d story cold air returns - I have two large floor returns on the 1st floor. He said since we have an open staircase we should be ok. I think he's trying to get out of work that is called for in the bid.

    Info: 1300 sq ft. two story home in Southern Michigan + full basement and unheated attic used for storage. Currently have a gravity furnace rated with an input btu of 135,000 and an output of 100,000. The current furnace seems to be a good fit for the house (on the coldest days it runs most of the time).

    My questions:
    What size furnace do I need?
    Can I add basement registers myself in or from the existing duct runs without causing equalization problems with the system? (I sure don't think it's worth paying him $1200..)
    What should be done to the existing ductwork in the walls? My neighbor suggested a larger blower due to the larger than normal ducts. Please give me any info you can so I don't end up with a big waste of money in my basement.
  • Dave_4
    Dave_4 Member Posts: 1,405

    sounds like i 100% guarantee that you will not be happy with this person.

    if your not happy with him now just Waite till you pay him to start work :-)

    get a pro and pay what it cost to do it right or you wont be happy. have the ducts balanced for each room

    get detailed quotes of what will be done to the (t)

    also pay to have a heat loss done on the house by someone that will come to the house not one done over the phone

    you may pay for it but just think how much you will spend on heating bills if some clown over sizes the system for you.

    a heat loss could end up paying for itself

    good luck
  • Darin Cook_2
    Darin Cook_2 Member Posts: 205

    At 1300 sq ft with a 90,000 btu furnace, you are telling me the heat loss is over 69 btu sq ft??? That is HUGE! Are all the doors wide open? You might approach the county about a weatherization program. It sounds like the shell of your home needs alot more work than the heating system.
  • Mad Dog_2
    Mad Dog_2 Member Posts: 6,691
    This!!!!!!! WILL cost you much more in $$ and aggravation

    not to mention the added extra cost of fuel that will be like a never-ending student loan that you have to pay every month. Get a real pro in there. You'll find the money somewhere else. Mad Dog
  • Empire_2
    Empire_2 Member Posts: 2,343
    Do you have a choice?

    Do you have to go with the lowest bidder? I find it hard to believethat any county could award a final bid to a project that was never properly sized. Your right Matt, sounds like a headache waiting to happen.
    Mike T
  • Steamhead (in transit)
    Steamhead (in transit) Member Posts: 6,688
    John, in Michigan

    I'd think there wouldn't be much need for A/C. Why not ditch the ductwork entirely and go hydronic? It will be much more comfortable than scorched-air could ever be and would use less fuel to boot.

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  • Darin(in Michigan)
    Darin(in Michigan) Member Posts: 90

    Where are you? I did six years in lansing and know several contractors in that and the surrounding area. If you're near Detroit, go with God. I was kind of lewd to believe that most governmental agencies throw out low bids and high bids to sustain fair practices between contractors. Follow that up with your local government.
  • Mitch_6
    Mitch_6 Member Posts: 549
    Why is it you \"must take the lowest bid\"

    In your posting you have already put up enough red flags.

    Lowest bid, site unseen.

    You state "The Bid States Must" sounds like your proposal to him, did you give him specifications and what did he give to you.

    Most contracts from contractors say "We Will".

    If you are concerned enough to post here you must know better.

    "Want to buy a bridge" Sight unseen of course!
    Just a poor joke but I hope you get the idea.

    Good luck
    Mitch S.

  • Leo
    Leo Member Posts: 770
    Govt Loans

    If you are getting a county loan to me it means you either qualify because of income or it is to improve certain neighborhoods. Is it a low or no interest loan? Given this it is coming from tax dollars right. Call the county guy and see if they inspect the work they are authorizing with tax money. Ask him if he thinks such a difference in prices means anything, if a county contractor needs to meet certain criteria. Around here they keep a copy of our license on file and sometimes prescribe how they want a job done.

    Good Luck on the project,

  • John Bonetti
    John Bonetti Member Posts: 5
    Thanks - and more info

    Thanks for all the responses. To answer some of the questions posed - we live in a Detroit Suburb (northern). The items I had in quotes was from the requirements the county gave the contractors. I'm interpreting it as saying that all the ductwork (including in the walls) needs to be evaluated and either replaced or sealed. One response (JohnT) mentioned that the walls would have to be opened up - my main concern is a horizontal run in my son's bedroom that runs under a wood floor about 8 feet and I know is loose (it lays loosely on the lath below it and stops before the floor register - it basically fills the joist space with hot air!). The rest are all vertical runs directly from the basement.

    Thanks for the input on furnace size - I got a clue that something was fishy when I went to the Trane website and saw that 120,000 btu was one of the larger furnaces offered. It is an old drafty house, but not excessively so. We feel more air coming in around our doors which are new than from our windows (which are original on the 1st floor with storms and are Anderson double hungs on the second floor).

    We do qualify for a low interest loan. We live in a very affluent area and although I make more than median income in the US, in this area, we're considered a poor family of four. We definately do not have a ton of money though, and I was hoping that the savings in fuel would cancel out the loan amount. Unfortunately, I need a new roof also (this was the main purpose for getting the loan) and we thought replacing the furnace with the same loan would make sense. Now I'm contemplating cancelling altogether. I'm going to ask them for a week's extension on making a decision since we currently only have until 5pm tomorrow (Monday). In that time, I'll get a company out here to do an analysis on our system and also contact the other contractors that bid on it. I really liked one of the contractors and he did take measurements of the house and added up the windows, etc. so he may have already done the study to some degree. He quoted $6000 for the furnace and removal of the old one (which also includes asbestos removal, I might add). The winning bid was only $2000. There were 6 bids total, and 5 of them were around $11000 (for the roof and the furnace, humidifier and bath fan) and the winning bidder came in at under $8000.

    I'm going to research home equity loans but the nice feature of the county loan is that from 20-40% of the work is interest free and payable upon selling or refinancing of the house. We would have only $35/month payments for 20 years on a $8000 loan. That's going to be hard to totally walk away from without trying to make it right. At least now I have some knowledge. I'm so glad I didn't just do it and took the time to research. Thanks to all of you for chiming in.


  • leo g_13
    leo g_13 Member Posts: 435

    if it were me I would invite the contractor that you are comfortable with back, and explain the situation. Is it not possible that they can do the work for their price, and you should still be able to get 8 grand worth of loan from the county?

    We have a Native reserve just down the street from where I live, and for the past few years they have been building houses for their members. Every memeber gets a basic house, and anything extra they want, they pay for themselves.

    Leo G

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  • Leo
    Leo Member Posts: 770


    The biggest thing is to bring this to the attention of the guy/gal doing the loan. If it is govt backed they shouldn't be wasting tax dollars. If the contractor is fly by night then they shouldn't be allowing him to be doing work under their program. It is things like this that give govt programs a bad name.

  • Darin Cook_2
    Darin Cook_2 Member Posts: 205

    Does the state of Michigan have a Energy Star program? Or some other sort of energy savings program? Paying a couple of hundred bucks to have a full blown energy audit done is going to help you in many different ways. The first being you will find out how many air exchanges per hour are going on. Critical information on doing a accurate heat loss. You will also find out how the air is infiltrating your home and where to seal it up. Air sealing is cheap to do and you can do it. Big savings on your fuel bill and a big increase in you and your familys comfort. I see no one else questioned the sizing of your equipment. That is troubling because your furnace should be in the rough neighborhood of 40,000 btu's or as close as you can get to it. That is just using a 25 btu' per sq ft guesstimate heat loss. Do you know where all those extra btu's go to when they do not go up the plenum? They go up the CHIMNEY!!!! YOUR HARD EARNED DOLLARS WASTED!!!! DO NOT have a heating system installed without further SCIENTIFIC investigation of what your home is really doing. Then you can decide what it really needs based upon building sciences fact rather than OPINIONS or GUESSES!! Fuel is never going to get lower so make the most of YOUR dollars now. I do not want to sound like I am beating up on you. I only want to see a good job done for you.

  • Mitch_4
    Mitch_4 Member Posts: 955

    Good lord man...first thing is to fix the 4' hole in the wall.. your loss is something like 70 btu's / ft sq. and the addition he is adding 100, Tell the idot to find the door...you will get more headaches (see Mad Dog's post)

    I am north of you in Ont, and I have a 1800 sq ft, side split with original everything including windows and a 9' patio door, open fireplace, and my loss is only about 50,000 (or at 80% eff a 60,000 mid furnace, whic I will use because I am adding a 400 sq ft addition and improving the envellope.)

    Try this site, and enter a s student:


    at lewast give you a ball park of the heat loss, or use the free software here. that guy is a ripper (gets in on htese,mthen tells you about the "additional charges"
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