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Typical Dimensions of a Gas furnance

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  • Typical Dimensions of a Gas furnance

    I am planning on replacing my electrical heating with a gas furnace that would be installed in my crawlspace which is 4 feet high. The opening to the crawlspace is 40 inches by 28 inches. The crawlspace is part of the warm zone of the house and has a concrete floor. Also, I plan on installing the duct work myself. It is a one story home and all the ductwork will go in the basement. If anyone can point me to a source of information for self installing ductwork that would be appreciated.
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  • #2

    Re: Typical Dimensions of a Gas furnance

    Have you installed ductwork?
    Its not really that easy.
    It needs to be designed but someone that knows what they are doing, not just thrown up.

    The local college will design duct runs (for a fee) that you can them diy.

    I would not recommend proceeding with a professionals designed plan.

    Furnaces have clearances & I honestly don’t know what they are off the top of my head.

    Whos installing the furnace?
    Who ran the gas lines?

    Your furnace guy would be able to to answer these questions better then me.
    Im a carpenter not a furnace guy.

    Duct work is a separate ticket above and beyond furnace/ gas work FYI

    Nathan

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    • #3

      Re: Typical Dimensions of a Gas furnance

      Nathan is right about the duct work. Mass amounts of efficiency depends on the ductwork design. Also I do not believe your furnace will work in the crawlspace. I installed my own furnace and duct work and one thing I learned during research is that a furnace needs a few feet of ductwork going straight up off the furnace before it does a 90* turn into the main trunk.

      I wasn't too worried about perfect efficiency out of my duct work as my house is 700sqft on the outside. Basement is even less. I did save about 80 per month getting rid of the baseboard heaters. If I was to do my own furnace again I would do what Nathan said and have someone design the duct work for me, lots of math that you need to know ductwork well to do. I've also bent a fair bit of metal so the duct work wasn't too hard and I have all the tools... it also wasn't easy dealing with 4ft pieces of tin.

      Answer to your main question, there is no typical size for a furnace. It depends on how big and what age and blah blah. But yes you could shove one through that hole (with a friend and cursing).

      I learned all my codes and regulations from friends and people I met on job sites. You could look it up on your municipal website I'm sure though. Even though I did everything myself with help from a friend, I had a 30+ year pro for every field I worked on on the other end of a phone.

      Installing a furnace is really easy. Designing duct work is NOT. A natural gas line isn't anything to mess with. Also intake and exhaust need to be done well for effiency and safety, can't have many fittings or length.

      Not trying to sound 'smart' here, good source for DIY duct work would be Google, try searching for 'duct work calculator'. Good luck!

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      • #4

        Re: Typical Dimensions of a Gas furnance

        I watched the men replace my electric forced-air with a gas furnace and was surprised at how many things they mentioned were required by code - things that I thought weren't really that important.
        billh

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        • #5

          Re: Typical Dimensions of a Gas furnance

          We are not trying to come across as super negative but furnace/duct working is not a diy project.

          Im good friends with a furnace guy, I can ask him some questions for you.
          But he’s not going to talk you through the entire process or design a duct system for you.

          Nathan

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          • #6

            Re: Typical Dimensions of a Gas furnance

            Some forced air furnaces can be installed horizontally or vertically to accommodate situations like low head-room so you will have options and choices to make.
            On forced air systems ductwork is an important part of the heating system so it needs to be right... ie, design and installation. and compatibility with the furnace.
            If I understand it correctly, natural gas-fired forced air furnaces and water heaters must be installed and vented correctly based on current rules ( no exceptions) so they are inspected and tagged at time of installation by a licensed gas fitter having that authority.
            Having just completed replacement of these systems in an older house my advice is work with an experienced heating contractor, and if your concern is $ , ask what you can do to help reduce your cost. In our case we provided labour to cut holes for floor registers and create paths for cold air returns, pick up materials from suppliers, run electrical wiring and cut floor drains for condensate and vent pipes etc.

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            • #7

              Re: Typical Dimensions of a Gas furnance

              One thing I remember about duct work code is that in Ontario, all heating duct must be 1" away from all combustible materials as in your floor joists. While searching for info I found that in new York, only the duct work within 3ft of the combustion needed this spacing. What I did was mount cement board all around the furnace and had my 1 inch gap to that and then just 1" gap to the joists every where else. Cold air can be right against wood.

              You'll need to know what furnace you have to know what cfm it puts out to start to figure out your duct work.

              Yes we are not trying to be negative. If you could provide an idea of where you live someone could probably give you more accurate advice. I don't know that much about a furnace but when I did mine I knew the codes for my area.

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              • #8

                Re: Typical Dimensions of a Gas furnance

                A tip I can give you for duct work is, it's a pain trying to get your next piece to go into the first piece. The joints connect with a 'z' shaped strip providing a female opening for the ends of the duct work to slide into. I always put the z strip on in a way that the next piece would be sliding over the first. Also cut the corners of the duct at 22.5* angle so it doesn't snag.

                Also I'm sure you'll want to keep the duct up as high as you can so it'll be a pain to get to that top seam. I ran mine beside the beam in my basement so I could tack a board across the bottom to hold the duct at one end while I messed with the other. I would have the duct sitting high at the one end so the top seam went in first. I also made a jig out of two boards and a scrap wire as rope. The jig held the next piece of duct square at both ends while I installed it and then could pull it out afterwards.

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                • #9

                  Re: Typical Dimensions of a Gas furnance

                  Lots of things to consider depending on where you live. Getting a furnace that will work is the easy part. Some furnaces even duct out the bottom. Gas line size, BTU's, efficiency, exhaust, Duct sizing and layout, Round versus square ducting, return air venting, fresh and combustion air intake. Fresh air into the crawl space, vertical or horizontal discharge, clearance under windows, future A/C. Gas meter????
                  "Do it Right!"

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                  • #10

                    Re: Typical Dimensions of a Gas furnance

                    This is only a DIY project for someone with lots of experience, and no to offend, but your questions indicate that you have neither the knowledge or experience to take this on. What are the permit requirements in your area? Will they even issue homeowner permits needed for this work? This is one project where it's very important that you have permits & inspections for the gas work & furnace/duct installations. There are many, many details that need to be dealt with properly in order to have a safe system.

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                    • #11

                      Re: Typical Dimensions of a Gas furnance

                      As an old heating contractor I will make a couple of comments. First I’m assuming that this is a renovation to your heating system and not a part of a building renovation that required a building permit.

                      A gas furnace will easily fit into your crawl space. It should be installed horizontally which will take up a lot of space and will require a good amount of thought and good design to accomplish a satisfactory result. A satisfactory result includes proper air flow and quiet operation while allowing for proper furnace venting, gas piping and condensate draining.

                      The gas piping and venting require licensed trade installation. The ductwork installation if done in your own home as a renovation should not require a licensed trade.

                      It is usual in a new installation to have a heat loss calculation completed, but no one is likely to require one from you. The same is true of a calculated duct design. Both are really helpful in having a safe, comfortable system. Around the Ottawa area there are accredited folks who charge about $800.00 to produce both calculations. Common sense allows most of these installations to proceed without the above designs, but there are lots and lots of really poor installations that are done not only by homeowners but by contractor/installers who should know better.

                      Trouble usually crops up due to over sizing the heating unit and/or under sizing the air delivery system. This can lead to discomfort and possibly cycling of the furnace on the safety devices.

                      Of course you can save a good amount of money doing the sheet metal install yourself. If you are a caring person and take your time, and have researched and designed properly you will end up with a comfortable, good looking system. But most people will screw it up!

                      Jim


                      Sent from my iPad using Tapatalk

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                      • #12

                        Re: Typical Dimensions of a Gas furnance

                        Thanks for all your feedback. I don't think I was clear in my original post. I'm not installing the furnace my self. I am just doing the ductwork. The house is 1000sqft and mainly open concept except for 3 small bedrooms and 1 bathroom. This was a cottage that was lifted and installed on a foundation with a 4 foot crawl space. Nothing too complicated on the heating runs. Straight trunk from end to end with straight branch lines likely 5 to each side. 10 in total.

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                        • #13

                          Re: Typical Dimensions of a Gas furnance

                          Well if this is part of a job that is under a building permit then the building inspector will almost certainly require the heat loss calculation and the duct design.

                          Jim


                          Sent from my iPad using Tapatalk

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                          • #14

                            Re: Typical Dimensions of a Gas furnance

                            To do your own ductwork you need a proper drawing and a duct shop that can make the ductwork. It's a bit tricky at first, but I did my house, to me that means almost anyone can do it.

                            Make sure to have lots of bandaids handy lol.

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                            • #15

                              Re: Typical Dimensions of a Gas furnance

                              You can buy all the duct work at a place like Rona except for the plenum that connects to the furnace or transitions if you need them.

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