Buying a new furnace and A/C

Hello all!
I will soon be moving in to a new (to me) house, and I have been advised that the existing furnace and heat pump are at the end of their useful lives. The house was built in 1971 and the natural gas furnace appears to be original to the house; the outside electric heat pump unit dates to the early 1980s and may have been the first A/C that the house had. The home inspector said that the heat exchanger in the furnace has rust holes in it, which is allowing combustion gases to leak into the house. The heat pump didn't have any obvious problems, but he said a 20-25 year lifetime was about right for this area. So it looks like I get to buy a furnace and A/C.
The existing furnace is a Lennox G8D1-82C forced air gas furnace, and the A/C is a Carrier 38QB036300 air-to-air heat pump. It is set up as a heat pump - for heating, if it's not too cold outside, it tries to run the compressor first before firing up the gas. (I didn't even know you could do that with a gas furnace, but apparently you can.)
The house is two stories total, with a basement (~50% garage, the rest of it two finished rooms plus the laundry and mechanical area) and a first floor (kitchen, dining, bedrooms, etc.) The basement is poured concrete and the first floor is wood frame with full brick veneer. It has a hip roof with regular composition shingles. The total floor area of the house is about 1400 square feet and the house is in the Kansas City, Missouri metro area. According to fedstats.gov, over 1961-1990, there were about 5400 heating degree days and 1300 cooling degree days at this location.
The entry-level replacement is probably an 80% efficient forced-air gas furnace and a 13 SEER electric A/C. Since I currently plan to be in this house for several years, it might pay to go for a 95% furnace and a more efficient electric A/C. Approximately what kind of a price premium am I looking at for 95% vs 80%? Is there a rule of thumb for what the payback period is? (The local gas company says gas is $1.09 for 100,000 Btu as of the first of February, but I don't know if that includes all the fees and taxes.)
Right now, the furnace and gas hot water heater share a metal vent that goes all the way up through the first floor to the roof. I understand that the 95% furnaces can use plastic vents because their exhaust is not as hot. Could a 95% furnace still be plumbed into the shared metal vent, or does it need its own vent?
I am not sure how much I like the idea of a heat pump. I guess they work well in places further south where you don't need that much heating, and running your A/C backwards for a few weeks a year is simpler and cheaper than installing some kind of burner in your system. But in Kansas City I wonder if it's a net win to just fire up the gas right away when you need heat. Any ideas? Are gas furnace + electric A/C heat pump systems still available?
The furnace was originally installed in an unfinished area of the basement, with its back to the partition wall between the basement and the garage. The return air comes in the side, near the bottom, and the heated/cooled air comes out of the top. Sometime later, more of the basement was finished, and the wall of the newly-finished part comes kind of close (maybe within 1.5 or 2 feet) to the front of the furnace. I can squeeze in there but not everyone could; I was advised that there is supposed to be more clear space in front of the furnace for servicing. If the new furnace could be turned 90 degrees relative to the current one, there would be bunches of room in front of the furnace, but I have the (possibly incorrect) idea that it's easier to turn one of these kinds of furnaces 180 degrees than it is to turn it 90 degrees. Is this true or am I confused?
If turning it 180 degrees is easier, I would need to cut a doorway into the garage; this is a non-load-bearing wall so that's not a very big deal. I figure I would take out at least two studs and cut the drywall back to make a four-foot-wide hole, let the HVAC guy do his thing, then frame it back to some reasonable door width and fix the drywall. Since it goes in the garage wall, I know this has to be a one hour fire rated door, without any vents in it. Any obvious flaws in this plan?
As far as sizing the system goes, there are lots of houses like mine in this area, so "same as next door" might not be a totally bad idea. On the other hand, paying a few more bucks to get it sized correctly now might save me a lot of money later - gas and electricity don't appear to be getting cheaper with time. Is it worth asking the installer to do a full heat load calculation for the house?
My plan right now is to call a Trane dealer, a Lennox dealer, and a Carrier dealer and get a bid from each one. These seem to be the "big names", and I've lived in houses with all three brands and had reasonable luck. (Although I think Carrier selling furnaces is a semi- recent development; for a while I thought they just sold A/C systems that were added on to other people's furnaces. I could be wrong.) I will give each one of them all of the information above, plus they will be able to wander around the house and see the current setup in person. Is there anything in particular I should ask the guy, or look for, when getting bids?
All three brands seem to have some kind of "premium super ultra nifty" rating for some of their dealers; is there any benefit to calling one of these dealers vs. one without such a rating?
One thing in my favor is that the house is currently vacant and my move- in date is a little flexible. I don't want to wait a month to get the new stuff installed, but I'm also not needing a new furnace RIGHT NOW at 10 PM on Sunday. :)
Thanks for your help!
Matt Roberds
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snipped-for-privacy@worldnet.att.net wrote:

Hi, First of all, find a reliable, honest, honbest installer and talk to him/her. You can find a good one if you try.
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On Feb 15, 10:28 am, snipped-for-privacy@worldnet.att.net wrote:

The now offer hybrids; gas over heatpump that might be worth looking into, Even as far north as you are there have to be lots of days where the heatpump could save $ & it will automatically roll over to gas heat when it gets cold enough that the heatpump is inefficient. I upgraded a few years ago, & went with Carrier infinity 96% propane furnace with an 18 seer A/C & it has definitely driven my bills lower + I got a rebate from the power company. If I were doing it today, I'd definitely look into the hybrid. What ever you do, try for the 5 ton A/C coil, it makes any size (except 5 ton) more efficient, and isn't cost prohibitive.
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snipped-for-privacy@worldnet.att.net wrote:

Hi, First step is talking to a BEST installer you can find in your local area.
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I like my Goodman family members have had goodmans for over 15 years.
The 90+ all vent thru the wall with pVC and its better to bring in outside air for combustion.
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Tony Hwang wrote:

Agreed. A competent installer is as important as choosing among the quality brands of hardware. Does anybody even SELL 80% units any more? When I replaced my setup a couple years ago, entry level they offered me was 92%. Note that new furnaces are considerably smaller in physical size, so the access clearance may not be a problem. The plenum will likely need to be redone, however. They will likely want to run the PVC vent tubes out the side, just above the sill plates. That also means dropping a smaller tube down chimney stack for the water heater, and changing chimney cap to match.
I'll throw in for laughs- how is the attic insulation? Adding six inches there saved me as much on the monthly bills, as going from a 65 to 92 furnace did.
-- aems ends...
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Trying to make a good decision on a large purchase like this can be a frustrating experience. It sounds like you are trying to think things through and make a good decision. I will try to answer a few of your questions. Gas furnace / heat pump combinations have been around for a while and are slowly becoming more common. While you can defiantly get by with just a gas furnace and normal a/c, you will save money down the road by using both. During milder outdoor temperatures (spring and fall) the heat pump will be cheaper to operate than the gas furnace. Even though electricity is more expensive, the heat pump will be around 130% efficient during the right conditions. The best you can get from the gas furnace is around 95% or so. You will spend more upfront for the heat pump but it should pay off after a while.
The pvc pipes for a high efficient furnace will need to be run separate from the water heater. This is because the cooler flue gas temperatures of the high efficient furnace is full of acidic moisture that will condense in the pipe and eat through the metal vent pipe or masonry chimney.
If you can get the heating company to do a full load calculation it would be a good thing. Most existing heating and cooling equipment in homes today are oversized. This causes them to run less efficient and will cause the house to be less comfortable than possible. It also causes the equipment to cycle on and off too often which is hard on them. If an air conditioner is oversized it will cool the house down really fast but it will not remove as much humidity, which will cause the home to still be uncomfortable.
It is correct that you will need ample room for service in the front of the furnace. This is something that will need to be corrected with the new unit. The install crew will figure out the best way to make it work.
Carrier, Lennox and Trane are the 3 top premium brands. Each company also makes less expensive branded units that are basically the same thing. Carrier is the same as Bryant and Payne, Lennox is the same as Luxaire, Trane is the same as American Standard. The proper installation is WAY more important than the brand and is the hardest thing to shop for. I would try to go with the company who spends the most time going through the load calculation and who answers your questions. Do NOT go with the cheapest installer. Check the better business borough. By the way, Carrier (and I believe all of the other mentioned brands) have been making furnaces since the days of gravity coal burners, although Carrier is known for inventing the modern air conditioner.
On Feb 15, 10:28 am, snipped-for-privacy@worldnet.att.net wrote:

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Don't take Eric in North TX's advice on installing an oversized evaporator coil unless you live in a dry area like Arizona. It will cause the system de-humidify poorly.
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On Feb 15, 11:42 am, snipped-for-privacy@hotmail.com wrote:

I hadn't noticed that with mine, but it does have a humidistat, and controls the humidity by running the A/C on low. This isn't a dry area like Arizona, but it is much dryer than say Pennsylvania. When it is humid here is on steroids.
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snipped-for-privacy@worldnet.att.net wrote:

The sensible thing to do is find the best installer and get a firm bid.
Then take the money and put it in a savings account or CD and wait for something to fail - it might be ten years, never, or your house might burn down next week.
Don't spend money unless you have to OR if spending now saves money later (OR, of course, you just WANT to spend).
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HAve you seen waht CDs are making lately. I replaced oprational 17 year old system with a new unit 2 years ago and I fugure the payback will be in 3 more years. MAybe less .
Jimmie
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JIMMIE wrote:

Oh, I agree, common investments aren't worth squat (Walmart sales, however, are up 8%). In your case, however, if a tornado blows your house away next week, there's two years worth of money gone, as they say, with the wind.
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If I were in your shoes, and if you plan to stay in this next home for say longer than 10 years, I would also assess/compare Geo-thermal HVAC. Figure double the installation cost, but significant savings to operate. On an existing home, a deep vertical trench needs to be dug in the yard to install the thermal loops.
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On Feb 15, 10:28 am, snipped-for-privacy@worldnet.att.net wrote:

With holes in the exchanger you dont want to live there yet-at all. A written load calculation is a must so you size it right, for maximum comfort in removing humidity in summer and even winter heat, your ductwork has to be assesed. Are you planning any window, door or insulation upgrades this year, then figure them into the load calculation. I did not and oversized my AC so im to humid all the time in summer. Utilities over the long term will go up so the highest efficency is an investment. If I were looking for a new unit it would have a stainless steel exchanger. I have heard some pros at www.heatinghelp.com [ a good place for you to post] mention problems with other types failing earlier then they should. You want a pro installer but should double check a few things yourself before final payment. Pulling a permit is cheap and gets you a free basic inspection. There may be utility and Gov rebates for Energy Star certified proucts. www.energystar.gov has ratings on just about all equipment made. Consumer reports has listed a long term poll done on customer satisfaction of furnaces
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Here's a link that should be useful that has a calculator to compare using nat gas vs a heat pump. You can enter the cost of electric and gas in your area and the efficiencies of the gas furnace and heat pump. It will then tell you the temp at which above it costs less to generate heat with the heat pump and below it's more cost effective to run the gas furnace. Then it depends on what the typical temp profile is at your location.
http://www.shoreviewtech.com/hp_temp.aspx
I also agree with the advice to look into the costs of geothermal. And check for any rebates, eg Fed, state, utilities, etc for all your options.
Regarding the high eff furnaces and the existing chimney, the high eff furnaces are direct vent, which is exactly that. They need a direct PVC vent to outside.
Regarding the geometries, and rearranging the furnace, who knows? That's where you need some pro's to actually look at it and give you recommendations and estimates.
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On Feb 15, 3:53�pm, snipped-for-privacy@optonline.net wrote:

check out a home with heatpump before buying their heat temp exhaust into the rroom tends to be less than a natural gas furnace
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