Furnace install Questions

Been doing some research and could use the help of the experts on a couple of things. I had 5 HVAC companies come to my house for estimates on replacing my 50 year old 90,000 btu furnace for my 1500 sq. ft. ranch in N.W. OH. The estimates where similar in terms of cost for most, so I am going with the installer that I trust the most and received good feedback on from references ( BTW - none of the installers did a manual J calc, most where just concerned with how to get the exhaust out). My questions for the group are these. 1) Do I go with a Trane or Armstrong, both are the 90 plus percent efficient, but the Trane cost an extra $425. What does an extra 425 get me? 2) The contractor I am going with recommended a flue liner for $210 for the hot water heater exhaust. Is that necessary/recommended, would it be better to skip the liner and route the water heater exhaust throught the same PVC that is being run out the roof for the furnace ( the furnace and water heater are next to one another) 3) Is it ok to run the PVC exhaust through an unheated garage to the roof. It will be hugging the wall, but do I need to insulate the pipe? 4) One installer recommended replacing the coil, while this guy said to wait. Why would I replace the coil, is it recommended? 5) As far as sizing, all the contractors quoted something different. The guy I trust the most said 60,000 btu but I had others that recommended 90,000. What are the implications of undersizing/ oversizing. Is a manual J calc absolutely necessary or is a trained eye who is familiar with the neighborhood construction able to tell from experience. Any feedback is appreciated.
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On Fri, 19 Oct 2007 05:02:02 -0700, Justintime

Look at the labels inside your current furnace. There should be a BTU rating somewhere. A close BTU match for your new furnace is what you atre looking for.
I just posted this in the follow up to a "no burner flame" problem in this newsgroup. Go to a major HVAC parts supplier in your city. Ask all the questions you have and also get a pricing for the equipment they charge everyone. Take a good look at their display model and get a good idea of the work involved. The dispaly model I inspected had an installation manual. Read that. That's all the required installation work the installer can do. Anything more or less can be a code violation.
I don't know enough to tell if one manufacturer has >$400 worth of technology over another. If you look inside to inspect how the furnace is constructed its hard to discern where one manufacturer could have make significant design differences to warrant that price premium. I'd go with the lower priced one.

My game plan was if the estimate from a repair guy exceeded $500 I would toss out the existing furnace and install one of those high efficiency ones myself. Mine looks new (well maintained) but its already 28 years old thereabouts. When the heat exchanger tubes give out, as they must some day not too far into the future, they will no longer be replaceable . By law the stores are not allowed to to stock them as replacement parts or sell any. Same with that $183 regulator. If faulty, replace only, no repairs.
Now if you HVAC guys can say this nicely, that your hands are tied by law (be prepared to show printed copy to customer) and give a best effort to do the simple fixes first, then perhaps you will get a much less hostile reaction from your customers. Explain what you did in repairs and why they didn't work. Gas fitting is not brain surgery that only HVAC guys can understand. Explain the problem solving procedures so that the customer knows they were something he could or could not have done. We all want to save a few bucks and this knowledge will satisfy the homeowner that its better to call you for fixes he'd realise as beyond his abilities.
Then give them the "bad news" a $3000 replacement or some equally shocking figure. Give them the name of your supplier so that they can check on prices. And also the opportunity to select a particular model. The customer expects to pay you something extra and reasonable as a markup for you to order and deliver the hardware for them. And to get rid of the old one. You charge service fees accordingly. The dollar amount won't be pleasant. But an honest breakdown of the costs that the customer can check on avoids a lot of unwarranted suspicions and bad impressions.
I went to a major appliance parts supplier store and they had a number of furnaces on display including the high efficiency ones. The panels had been removed so it was easy for me to make a close inspection of its assembly modules and installation requirements. To install a high efficiency furnace is a lot easier than to service one. Specified PVC ducting for the air intake and burner exhaust. The gas connection and the electrical connection. That's it.
The new furnaces are shorter than the old gas furnaces. A transition plenum will be needed to connect the shorter) new furnace to the existing hot air plenum. My intended adaptation will be to instead make a steel stand to raise the furnace to the existing plenum. That way the bottom of the furnace will be off the floor and free from any dampness or standing water. My existing furnace is resting on spare aluminium bath door tracks and its free from rust and grime.
I chatted with the store personnel and they didn't bat an eye on my intent to do the installation myself. In fact they gave a lot of pointers on things I should do, such as resizing the hot water heater exhaust vent (to a 4 inch liner) as my existing stack will be too large. I found the same information in the installation manual. But I still appreciated the information as it gives me the right information to make my installation plans in the meantime.
The basic high efficiency furnace model is $1300. I can budget for that.
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PaPaPeng wrote:

PPP:
That's true if the old one isn't oversized, but a lot of them were, especially if the insulation was upgraded since 50 years ago.
I think an experienced HVAC pro who was familiar with similar houses in the neighborhood, especially if it's a development of almost identical ones, could have a pretty good idea what furnace to use, but I'd still like to see calculations done. My feeling is that somebody who just won't do the math either doesn't know how, or else is too proud to admit that a guess might be wrong, and I can't say I like either of those options. I'm not a furnace man, but in other areas I am always finding out that experience is something that needs sanity checking.
OP, a furnace is something you won't have to buy for 20 years or so, and Trane is a good furnace, so if you can afford the extra cost I'd say to go for it. I think I would like to see some kind of heat-loss calculation done, however.
As for the water heater, I don't know what kind it is. I don't think you can vent it through the same PVC, even if it's a power-vent type, and if it's an ordinary heater it will need to use the chimney, not PVC. Is the contractor you are using, who recommended the liner, the one you "trust the most", as mentioned below?
G P
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On Fri, 19 Oct 2007 09:55:04 -0700, snipped-for-privacy@gannon.edu wrote:

Should the high efficiency furnace be installed then the PVC pipe intake and exhaust for this furnace must be entirely separate runs and nowhere near the hot metal flues. I am convinced about the high efficiency claim because the waste gas coming out at the furnace plenum is cool enough to put one's hands around them. In the old style furnaces that will be too hot to touch and that's waste heat going up the flue. In fact keep the PVC piping as far away from the current exhaust's stack on the roof to avoid the PVC intake sucking in poisonous exhaust gasses. My preference will be to run the PVC through a side wall to reduce the run length and the convenience of just making two holes through the floor joist instead of running them through the first floor, the ceiling and roof. And I will have to do this in a way that the PVC pipes won't intrude into the decor of the house insides, keep a respectable distance from the hot water exhaust flue........ too much of a hassle all round.
My hot water heater's 4 inch flue is connected into the main 6 1/2 inch flue for the furnace. This is made of galvanized steel sheet and too hot to touch when the burners fire up. The now disconnected from the old "no longer there" furnace 6 1/2 inch flue will certainly be too large to vent just the heater waste. It will likely risk having hot water heater exhaust gas blown back into the basement (or the rising hot exhaust may drive a convection current up the flue thus drawing useful heated air from the basement??). The installation manual recommendation is to run the 4 inch flue all the way up through the roof as a liner inside the 6 1/2 inch pipe. That way you don't need to do any major work cutting through though the ceiling, roof, flashing, etc. You cannot run the PVC piping up the same 6 1/2 flue as the hot 4 inch flue will melt the PVC pipe. I have a high and very steep roof and the run is equivalent to two floor lengths. It worth to me the $250 asked for the labor and materials. The material cost is minimal. The other contractors may have included this in their quote without identifying it as a separate item. This modification should be mandatory. It would be a negligent for a installer to omit it and force the homeowner to correect the omission at a later date.
As for BTU calculations it takes only a grade 8 qualification to enter a Trade Apprenticeship program. Doing math is not a strong skill. I can understand their reluctance to provide the math. The current furnace should give a strong feel as to whether its undersized or oversized. Go from there.
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Re Re: Furnace install Questions:

Bingo! The OP never said anything about the replacement being motivated by over/under capacity of his old unit.
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Yes, but he did say the old one is 90,000 BTU's and 50 years old. And he said absolutely nothing about what the duty cycle of it has been in typical winters. If he has one that's already over size, and he's getting a new one that's maybe 25% more efficient, why should he over size it even more by going with the same BTU?
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On Oct 19, 5:32 pm, snipped-for-privacy@optonline.net wrote:

Size it by a load calculation , you may only need 40000 BTU, who knows, who cares,. New high efficency units waste less and give more heat . I cut my btu from 110, 000 to 47000 and its still to high, a new load calc put it at 35000 , R 110 attic helped............
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wrote:

What type of crack are you on??? Since when can't you change out the burner tubes or heat exchanger??? Why don't you stop posting on things you know nothing about???

Really, no condensate drain? No testing or other required hook-ups or steps???

Can you buget for your stupidity???
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This post is more to show homeowners how to debunk trolls like kipro than as a reply to him.
Okay, I missed mentioning this item since its not an immediate task (installing the furnace) for me to keep in mind. The condensate hookup is in the installation manual. More to the point the label right beside the condensate collector in the furnace tells whoever is reading it what must be connected and why. Its just a tube into run to a drain to get rid of the water condensate.
As for the rest, after self installation, get it inspected by the appropriate authority and be certified as correctly installed. There isn't any secret magic stuff that only HVAC trolls can do.
In my Province I can do my own electricals and plumbing too. If I got myself maimed or killed, tough. Its not a crime. My neighbor, should I damage his property in the process, can sue me. The insurance company can refuse to pay for self inflicted damages. Otherwise I can do anything I want to and inside my house short of buring it down and endangering the neighborhood.
Had I not been in such in a hurry I could have repaired my furnace regulator (already done) and saved myself $138 bucks. But I had already installed the new one. It would be unethical for me to uninstall it, put back the repaired one and return the new regulator to the store for a refund.
I can certainly replace the heat exchanger tubes too should I be able to get my hands on some new ones. By law the appliance part store cannot stock or sell any. I took a look and (mine) the tubes should be good for another ten years at least.
However, if you work in the trade the Provincial laws clearly state that you can only replace the gas regulator and cannot do any repairs. You also cannot replace heat exchanger tubes. If our Kipro from Hell insists on doing that in my Province he will lose his license and I can sue the pants off him for, in law, endangering my life and property.
As a general rule, for modern day equipment, that is anything 20 years old or younger, they are no longer designed for parts repairs. All the service technician does is to swap modules. The main consideration is will a complete new piece of equipment cost significantly more than the cost of parts and labor for a repair. If fixing the old one is half the cost of a new one a better option is to toss out the old one. The new one will give you more years of trouble free service than the hassle of recurring small problems with the old failing one. This module swapping design philosophy also means that fixing a faulty piece of equipment something you can do yourself without having to master some complex skill and special schooling.
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It's simple, don't post inaccurate bullshit and I won't point out your ignorance.
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