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I’m building a place in the sticks and I’m doing everything myself. I plan on using a direct vent hot air system. I was wondering if anyone knew of a good site for info on furnace installation and duct sizing and installation. I’ve installed furnaces before but the requirements were very simple. I’m building a split level with a complex plenum. I also want to make sure the ducts are the right size to balance air flow and keep air velocity high without causing to much back pressure. No I am not going to hire a contractor. I can buy a top of the line Lennox with plenum and all duct work, filter and air make-up unit for three grand. Where the house is they want eight grand for a Ruud and installation. I don’t know about you but I don’t get paid 5 grand a week and I’m a Network Engineer.
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Replies
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Jerry,
Post your question on http://www.hvac-talk.com. They have a residential HVAC section. You'll get lots of feedback.
David
*And not much of it will be very respectful or supportive of DIY. HVAC is a mighty good area to spend a little money for someone else's expertise.
*Best site for DIY furnace installation is http:www.ISureHopeMyLifeAndHealthInsurancePoliciesArePaidUpAndTheWillIsInTheSafe DepositBox,Honey.com
*Jerry,Try http://www.darwinawards.com/KK
*Jerry: I'm not going to flame you for wanting to do it yourself. Jeez guys, he said he has installed some furnaces before and he is clearly trying to learn and gather information before starting. Does anyone ever know everything before sailing around the world, building an airplane, or the perfect house? Fortunately Magellan, the Wrights, Rutan, and I decided to go for it anyway. In my case I opted to do all my plumbing and heating mostly because I wanted to and it's fun. Had experience on a few hundred paid jobs but tackled things I'd done before. And in my area, I'd seen so many crappy, $9,000 installations that didn't work when the first "professional" plumber left.Jerry: Duct sizing is ideally done by calculating pressure drop for each leg and balancing the flows while staying under the pressure limits of the furnace's blower. email and I can USMail you the appropriate charts. The fine little lines don't fax well. Most of the pressure drop is in the fittings, a point that eludes some people.Do the guys who install most furnaces do that? No. If 6"x10" rectangular comes out of the furnace, you continue that or transition to 8" round to maintain the cross-sectional area. Then at each split, you maintain total cross-sectional area while balancing the size of each branch to the area of house it serves. (e.g. a split going to 1000 sq ft and 2000 sq ft could go from 8" to 5" and 7" - a perfect 1:2 between the branches and more than maintaining cross-sectional area.) In practice this is modified greatly by what will fit within the bays and what sizes are on the truck.Do that and put in some accessible balancing valves and you'll be fine. Adjust the balancing valves after a week based on your experience. Then fine tune the system again after a year using what you've learned through the seasons. I've got "summer" and winter" marked on my system because 5 versus 20 hours of solar input makes a difference. -David
*"Jeez guys, he said he has installed some furnaces before and he is clearly trying to learn and gather information before starting. Does anyone ever know everything before sailing around the world, building an airplane, or the perfect house? Fortunately Magellan, the Wrights, Rutan, and I decided to go for it anyway."There are so many non-obvious ways to screw up a furnace installation that, IMO, one should be well up a formal learning curve before trying this at home, kids.How many people died before Magellan? Before the Wright Bros?I think designing the plenum and duct system is a great idea. With some work and study I'll bet he'll be miles ahead of a great many HVAC types!Plus the duct system is not likely going to be deadly (unless he puts a return too close to the furnace in a retsricted area) but there's other stuff that can be deadly.The fact that he's installed some furnaces before doesn't mean anything. BTW, I noticed you didn't include brain surgery in your list of DIY fields
*Bob...I can do brain surgery....Come on by some time...near the stream,aj
*Bob: Only two died that I am aware of before the Wright Bros and Magellan himself died on the voyage, but some of the party made it whole way.Will someone installing their fourth furnace do as well as someone who has done hundreds, been back to see old installations, attended manufacturer's trainings on a regular basis, and studied a bit of engineering, toxicology, and climatology? And of course, understands all the other aspects of house construction thoroughly (like some of FHB's consultants.) Probably not. Does someone like that do the work when you call "Double-A Dan's Heating and Cooling"? Probably not.
*Jerry:I have seen many DIY installs that worked out just fine. Have also seen a bunch of "Professional" installs that were pathetic to say the least. So do your homework and you will work out just fine.Like David says the two biggest decisions are duct sizing and sizing the furnace. The manufacturer can help with the furnace so you get one that is right for your size house. The biggest sin of most contractors is to install too big a furnace. Lots of duct sizing helps around. Get the one's Dave has and work from there. Also check with your local building department; many communities have energy standards that you must meet.The flames you've got from some people makes me think they are scared you might find out just how easy designing and installing a furnace system is. The key to this is just like the rest of the house: Pay attention to details.
*I've got to second Fred's thought about many furnaces being oversized (since I forgot to mention it). A HVAC guy doesn't get called back if the furnace turns on and off every 5 minutes even through it is an annoyance and shortens the life of several components. An HVAC guy only gets called back if there is not enough heat. So it behooves them for both PR and financial reasons to round up at a minimum and to more commonly, oversize the heating system.It is worth the minimal time and expense to do a rough energy audit (+/- 20% is fine). And buy a unit that will run 80-100% of the time on your design temperature coldest day (-40F for me). Worst case, if your estimate is a bit off and it actually gets down to -45F one week in the next decade, you'll have to wear a sweater or plug in an electric heater or two for a few days. BFD.But you will have a system that produces much more even temperatures and is, to a greater extent, either running or not. As opposed to turning on and off continually which is more noticeable and annoying. The furnace will also be a bit smaller and cheaper. Something I never see discussed is the space that the utility room takes up. If houses cost $100-200/square foot and you can save 20 square feet (such as combining water and space heating in one unit), isn't that $3,000 in your pocket? In addition to the details, as Fred said, another key is RTFB ("Read The Fricking Book"). That installation manual isn't just to tape on the side of the unit. Lots of good info in there. If it's been a few years since I last read one for a pump, heater, or whatever, I always learn (remember?) something by rereading it. -David
*Thanks for the help. I know there are a lot of people out there that do stuff themselves because they don't care to have it right. My problem is I have a budget and I want it perfect. I've had several different professionals on this project all of which I would never hire again and some I had to fire before they were done, and then I had to go back and tear out what they did and do it right myself (Including ripping out the entire basement and garage foundation). I have paid very close attention to what the code is for different things and the reason for the code. If anything I'm a safety freak. I have recieved factory training on installation of furnaces and AC units for large travel trailers and mobile homes so I'm not ignorant of how these systems work. Rest assured you won't be reading about me in the papers. I'm actually going to check out the local colleges to see if they have courses on HVAC that I can take. What I'm really looking for are the tips and tricks, the things you don't learn in a book. The time savers, like whats the best way to cut into a plenum to attach a branch, that type of thing. The place I'm building is 2300 sq. ft. in northern Michigan, I've talked to several contractors and they all agree that the furnace should be 125,000 BTU. Because I may be shutting the place down in the winter and coming up for weekends, I will need a little more capacity then you would typically size for. Hey guys not everyone who posts here who wants to do it themselves is an idiot. I was a certified auto mechainic at age 17, certified RV mechainic at 18, high pressure hydraulic and pnuematic pipefitter at 19, machine tool electrician at 21, Electrical Engineer at 25, besides being a welder, machine repairman, carpenter, computer technician and computer systems engineer.So far the local inspectors have said this is the best work they've seen around here, so I must be doing something right.
*Hey, don't sweat the flamers, Jerry.Most of the people here are helpful and thoughtful. Just some of them are touchy (and some are both, on alternate days).Keep us posted on your project (and the rest of us can learn from you!).
*David and Fred are right on. As to duct size, one DIY solution is to use the biggest that will fit consistent with what you can get free or at the scrap yard, which are my preferred sources/method (e.g 22" dia 14ga steel ducts for $10 for 20 feet, etc.). There are easy use ducting charts in "Std. Hndbk of Eng Calc", T.G. Hicks, McGraw Hill that library should be able to locate for you. Have you considered a heat pump? Packaged units are precharged. Cost comparison chart attached that I used to choose heat pump over other options last year, Seattle area, chart based on 4800 sq ft heated, 5500 deg-days - (wife said 57+ was getting too old to cut/split her share of firewood). Even a split system HP is easy DIY with your abilities, you can get freon license by taking a simple test on the net for $25, but you would need to make/buy vacuum pump, etc.
*Jerry, a P.S. - found best HVAC non-surplus DIY prices were thru Grainger (some net sites close in price, but shipping a killer), none of local Carrier/Trane, etc. distributors would even talk to me (other than trying to refer to contractor. Paid $2100 for 4ton Rheem last year.
*I did consider a heat pump but there were a couple of things I had to consider, If I close the place for the winter and decide to come up for a weekend, I have to get the house from -20 to 70 in reasonable amount of time (with the help of a wood stove), also a heat pump requires more electricity then gas. Power tends to go out often and usually for a couple of days so I need to be able to run off of a generator for a while. I have a source for everything thing I need, I was planning on using a Lennox direct vent so I don't have to run a chimney for the furnace. By the way I was quoted $2950 for 125,000 BTU furnace, Air Bear filter, Scuttle air make up and all duct work. I'll send a picture when I'm done.
*You might consider powering the furnace and blower through a receptacle rather than hardwiring it in. (If okay with your inspector). Then is it much easier to power with a generator. Just throw an extension cord out the window. I went that route.Because my only electrical demand for heating is a few 1/40 and 1/25 hp circulator pumps. So I can run them off an inverter and either a storage battery or the car. Haven't had to. But at -30F, it's nice to have options.The totally spiffy thing would be a proper electrical disconnect and subpanel for the generator. FHB featured a year ago? If not, at least make it easy to run the heat. Move the ice cream onto the porch and the milk to a ice chest on the porch. -David
*"Hey guys not everyone who posts here who wants to do it themselves is an idiot."Now that you've posted your qualifications, I say go for it.I still stick to my original response, however, for "just anyone" who asks that sort of question.I do home inspections. I see a lot of amateur work on furnaces, and the more I see, the more scared I get. (Of course, I've seen some "professional" work that leaves a bit to be desired, so I suppose to be perfectly consistent, I should advise chopping a hole in your roof and floors and using an open fire )"I have recieved factory training on installation of furnaces and AC units for large travel trailers and mobile homes so I'm not ignorant of how these systems work. "Be aware that the mobile home and manufacturered homes (at least the ones I've seen) use a very different type of furnace that "regular" homes. I don't know why.
*Bob: Perhaps mobile home heaters are different because they have the option to use propane? And propane is a scary thing due to it's ability to collect in low spots. Or maybe just because mobile and manufactured homes cut every corner, financially tha they can. -David
*David,I don't know why, but every time I see one (only a couple of times a year) I feel like I'm out on one of my early inspections: ("Hmmm, what the hell is this?")I see propane fairly regularly; "standard" furnaces but with different burners.
*Jerry,I don't know where to go to find information on learning to install furnaces and to size ductwork. I know how to do these things, but learned from an "old hand" and experience.The steps are:-determine the building construction and run heating loads (you mentioned nothing about cooling) for each room you plan to heat.-pick minimum sized the unit based on design conditions, and the loads. If the load fall between available sizes, pick the next larger size for heating (next smaller for cooling).-determine the air flow required for each room (ratio the room load/total to the unit total air flow).-size ducts to provide the max flow at 0.05" to 0.08"/100 ft of pressure drop. You'll need to find a "ductulator" or duct sizing calculator for this, find a wholesaler in your area, they'll probably give you one.-size supply and return registers, supply at no more than 700 fpm face velocity, and 500 for returns. Again, you'll have check vendor data to find velocities for their products at given flows.-locate supply and returns to get the best cross flow that you can, for heating best to have supplies at cold spots (i.e. doors, windows, exterior walls...) and returns on the opposite side of the room.As far as installation of the furnace, follow the manufacturer's recommendations for venting and you should be OK, check out the applicable Mechanical Code, to be sure. If you go with the direct vent furnace, glue all pvc joints and be sure not to restrict the exhaust with something like a bird screen.Final considerations that make a difference is seal duct joints with tape (real duct tape) and take-offs with polyeurethane, wrap and tape ducts in unconditioned spaces and install volume dampers in all branches. Use supply and return registers not grills.
*Jerry....I totally agree that you are fully capable of building out a super HVAC system...I also think most mechanically inclined can...My point on this board often is that Main panel electric work is just not the best thing for most people to play with just to save money on a one time expense. But even main panels can be tackled by most if they have enough desire and learn enough about the basic dangers.Good luck...post pics of your work when complete.near the stream about to upgrade my own heat source,aj
*I downloaded HVAC-Calc and will put the numbers in and see what it comes up with as far as heat loads. I din't mention cooling because I'm on Lake Huron and an attic fan will more then do the job in the summer. By the way any favorites on what furnace to get. I got a good price on a Lennox, but I'm seeing a lot of mention of Carrier on this board. Someone mentioned staying away from main electrical panels, where I'm at I even had to run the service on the pole myself.
*Every major manufacturer that I am familiar with has a range of products, from low budget crap to higher budget crap. Nobody in the residential market is exceptional. Features are more important than name plate. Shop and compare. Proper unit sizing and good ductwork, is more important in a good system that the burner/blower unit.BTW, I beleive a knowledgeable homeowner will always do a better job than a contractor trying to make a profit. The key is knowledge and ability. 50/50 chance a contractor will have either and he always looking after his bottom line, not yours. However, bending sheetmetal is a specialty.
*What I'm really concerned with is the reliability of the electronics. When I first started working on furnaces, electronic ignitions just started coming out. I was replacing ignition modules like crazy and they weren't cheap.
*Electronic ingintion is pretty much the standard these days and reliability is no longer an issue. I have a middle quality, 7 year old Bryant, never had a problem.
*
I'm building a place in the sticks and I'm doing everything myself. I plan on using a direct vent hot air system. I was wondering if anyone knew of a good site for info on furnace installation and duct sizing and installation. I've installed furnaces before but the requirements were very simple. I'm building a split level with a complex plenum. I also want to make sure the ducts are the right size to balance air flow and keep air velocity high without causing to much back pressure. No I am not going to hire a contractor. I can buy a top of the line Lennox with plenum and all duct work, filter and air make-up unit for three grand. Where the house is they want eight grand for a Ruud and installation. I don't know about you but I don't get paid 5 grand a week and I'm a Network Engineer.