Results 1 to 6 of 6
  1. #1
    Join Date
    Oct 2005
    Location
    Milwaukee WI
    Posts
    3
    Glad to have found this forum, hopefully some of the experts/pros here can chime in with a response to my post. With Nat Gas prices going way up, and the fact I have a 30+ year old (Singer) unit running, I decided I better look into replacing the furnace sooner rather than later. Since my experience in this area is pretty limited to just maintaining this old unit, I am at a bit of a disadvantage on the subject. A couple of things I am trying to do.

    1)Get a general sense on how much my energy savings will be by going from this old 60% AFUE Unit (100,000 Btu) to a new unit.

    2)Try to pick out a dealer/brand I can trust in terms of quality workmanship and a fair price. Carrier & Trane are the 2 most significant brands I am aware of. (Due to the nice big marketing campaigns they put on). Basically trying to avoid getting screwed with either bad equipment/dealer/price.

    Part 1: When attempting to determine how much I may save by upgrading, I downloaded the last 5 years worth of gas & Electric data on a month by month basis from We-energies. I was able to factor out the gas usage for the dryer & water heater using that data, but now I am just wondering if I have the following part correct.

    Going from a 100K to 60K unit (40% less usage top start with), then factor a 30% improvement in efficiency over the old unit.
    Example:
    Feb of 2005 we used 120 Therms of gas for Heating the house. So the equation would look like this: (120*.60)*.70 =50.4 therms with new system. Now my initial guess is that the 40% reduction in usage due to the size correction is likely to be an over estimate, and not in fact a 1 to 1 relationship. But what should I factor for it then? Also is it reasonable to use the 30% improvement due to the better AFUE, or should I back that off a tad?


    Part 2: So I called a Local Carrier Dealer here in Milwaukee, WI and had him come over and give me an estimate. Fist off he stated that the 100K Btu unit was much too big for my house. 1200 Sq Ft Cape Cod 1 ½ story type. The unit he recommended is a 60K Btu 90%+ AFUE (58MCB- a “builders” series of the 58MCA, only “real” difference being warranty of 20 years on heat exchanger VS Lifetime, and a different front on it.) The Quote also included a Bypass Humidifier & High Efficient Air Filter, Condensate Pump plus all the usual extras/basics. My Electric is good, Ductwork is good, Thermostat is good. Central Air unit quoted is a 38TKB 2 ton/24K btu Carrier.
    From what little I can tell this dealer has a “good” reputation here in this area.

    A few people I have talked to felt my quote was “kinda high” sounding to them. One of them recently had a new furnace & A/C unit put in, in a bigger home for less (~$XXX, which was a 3 ton A/C Unit, but upon further looking into it, he got a Ducane 80% AFUE unit, and the A/C is a Concord, some brand I had never heard of, or read about, but his system seems to be doing a fine job for him so far. But the systems being quoted really aren’t apples to apples). This did make me wonder however, should I be just looking at a 80% AFUE? Can I mix a different/less expensive brand of A/C Unit with a Carrier Furnace? For that matter should I? Is a Carrier Furnace worth Twice the Price of a Concord? Should I be looking at a different brand, as far a the better price/performance/reliability mix?

    My Sincere thanks in advance to those who respond with any help/ideas.



  2. #2
    Join Date
    Sep 2005
    Location
    San Jose, CA
    Posts
    22
    Dilbert,

    Your current unit is 100kBTU and 60% so you are getting approximately 60kBTU out of the existing unit.

    If you upgrade to a 90% then you will be increasing your current efficiency by 50% ( 90% vs 60% ).

    If you stay with your current output of 60kBTU then that would be provided by a 90% unit running at ( 60 / .90 ) = 66kBTU.
    Going with a 60kBTU at 90% AFUE would give you 54kBTU, very close to the 60kBTU of your existing units output.

    I am not an HVAC person so if I said anything wrong, I am sure a professional will step in and give a more correct reply. (just don't ask about flowing nitrogen. Thats an inside joke. fully beaten to death in another thread.)


  3. #3
    Join Date
    Mar 2004
    Posts
    1,042
    First, I am stunned at your gas consumption for February, given the climate and having an ancient furnace. It must be well insulated!

    Don't assume usage based on equipment sizing. You can run a 120kBTU burner half the time or 60k burner all the time, and the gas consumption is equal. That said, with everything else being equal, you will get better efficiency using the smallest equipment that can get the job done- so you would waste less heat out the flue with the 60k burner than the 120k burner. A heating system that's too large for the job will not achieve its rated efficiency.

    If your old unit was 60% efficient, and you upgrade to a 90% unit... let's use your February 2005 data as a test case. How much heat did the house actually use, and how much went up the flue?

    120 therms = 12,000,000 BTU (1 therm = 100,000 BTU)
    12,000,000 * 60% = 720,000 BTU went into the house.

    To put 720,000 BTU into the house with a 90% efficient furnace, you need 720,000 BTU / 90% = 800,000 BTU, or 80 therms of gas consumption. From there you should be able to figure the cost savings, given your gas rates (and how they may be changing...)

    I can think of very few cases in your part of the country where getting an 80% furnace really makes sense. You're on the right track with a high efficiency unit. Dual fuel is not a bad idea, either, since you're going to be replacing the outdoor unit anyway. In that system you use a heat pump for heating whenever it's above freezing outside, and use a regular furnace when heating when it's below freezing. In nonfreezing temperatures heat pumps are much cheaper to run than any sort of fossil fuel furnace. There's not much price difference to get a system set up for dual fuel when you're already replacing the AC unit and coil, so it won't be hard to recover the extra cost in utility savings. This setup is all the rage this year, with natural gas rates rising so quickly.

    We can't address your price question directly. I would agree that you aren't comparing apples to apples at this point. That's just one more reason you should get more than one bid!

    If your old system was in fact that oversized, you may actually need a unit one size smaller than the contractor proposed. It does seem a little odd that he said you were greatly oversized, and then proposed a unit with an output just 10% smaller than what you have now. To get the sizing right (guesstimates are right out!), have a contractor do a Manual J calculation on the house, or do one yourself. You can buy the homeowner version of HVAC-Calc software on this site for $50. That will tell you the right size equipment to use based on industry standards instead of guesstimates. Just be prepared to spend a lot of time measuring rooms, inputting information on your insulation, etc., if you do it yourself. I did it as a homeowner, last year, and it took me several hours. The results were excellent, though.

    [Edited by wyounger on 10-13-2005 at 03:42 PM]

  4. #4
    Join Date
    Oct 2005
    Location
    Milwaukee WI
    Posts
    3
    Originally posted by wyounger
    First, I am stunned at your gas consumption for February, given the climate and having an ancient furnace. It must be well insulated!

    --Actually I think it's appaling how little insulation it has! Built in 1952 when they didn't do much insulating. On the plus side I replaced the old drafty pathetic aluminum windows with current "new construction" windows. Low E, Argon gas etc. That quickly patched 10 holes. (including a really bad Bow window). We also have a programable thermostat and use it effectively adn we don't keep the house very warm in the winter ~66/67 degrees at most, 62 at night.--

    Don't assume usage based on equipment sizing. You can run a 120kBTU burner half the time or 60k burner all the time, and the gas consumption is equal. That said, with everything else being equal, you will get better efficiency using the smallest equipment that can get the job done- so you would waste less heat out the flue with the 60k burner than the 120k burner. A heating system that's too large for the job will not achieve its rated efficiency.

    ---So the old Singer unit probably isn't even hitting the 60% AFUE then. From the way you are laying it out my assumptions on how to calculate the savings were way off. I pulled the 2003/4 heating season, & the 2004/5 season and ran the usage numbers and we were at 585 & 584 for those 2 periods. (Hey were real consistent!) Now I will try to use your forumla and see what kind of savings we may see.
    ----Wow from 585 down to 390!


    If your old unit was 60% efficient, and you upgrade to a 90% unit... let's use your February 2005 data as a test case. How much heat did the house actually use, and how much went up the flue?

    120 therms = 12,000,000 BTU (1 therm = 100,000 BTU)
    12,000,000 * 60% = 720,000 BTU went into the house.

    To put 720,000 BTU into the house with a 90% efficient furnace, you need 720,000 BTU / 90% = 800,000 BTU, or 80 therms of gas consumption. From there you should be able to figure the cost savings, given your gas rates (and how they may be changing...)

    I can think of very few cases in your part of the country where getting an 80% furnace really makes sense. You're on the right track with a high efficiency unit. Dual fuel is not a bad idea, either, since you're going to be replacing the outdoor unit anyway. In that system you use a heat pump for heating whenever it's above freezing outside, and use a regular furnace when heating when it's below freezing. In nonfreezing temperatures heat pumps are much cheaper to run than any sort of fossil fuel furnace. There's not much price difference to get a system set up for dual fuel when you're already replacing the AC unit and coil, so it won't be hard to recover the extra cost in utility savings. This setup is all the rage this year, with natural gas rates rising so quickly.

    --Cost is a real significant factor as I will have to borrow to pay for the unit. The dealer who was in never mentioned dual fuel.---

    We can't address your price question directly. I would agree that you aren't comparing apples to apples at this point. That's just one more reason you should get more than one bid!

    ---I realize that is a forum rule which I why I kept any actual prices that is was quoted out of my posting. Still, as a consumer I find it amazing that the pricing information on HVAC is as "tight" as it is. I am going to get at least 2 other quotes, including a Trane dealer as well in the mix. The other question I had posed was more of a Value question. Does it make sense that a 2 ton Carrier A/C unit would cost twice a 3 ton Concord unit does? Essentially can you go with a lesser name and still get a reliable unit and save some, or are you really gambling on the lesser name?----

  5. #5
    Join Date
    Mar 2004
    Posts
    1,042
    Price varies more by model line than by size. For any given model, the price difference between a two ton and a three ton is actually very little.

    What drives price more is 1) name/reputation/advertising 2) model range and 3) efficiency.

    You can buy a builder-grade Carrier for a price that won't be as far off from a cheap no-name as you might expect, but neither of them are going to have the pressure switches that prevent equipment damage. Both are going to be pretty noisy. Barebones, entry level stuff. Note that you can get builder grade, for the moment anyway, in 10 SEER, 12 SEER, 13 SEER, 80% AFUE or 90-92% AFUE.

    As you step up into mid-range and nicer models, the equipment starts getting quieter. Built to last longer... better control systems, designed to protect the equipment from abnormal conditions and to provide better comfort. Mid-range models are available in just the same efficiency range as builder units. They're just built differently.

    Then of course there is top end equipment, which, of course, has the best of everything, and the highest price.

    What is confusing is that a big-name builder grade unit may cost as much as a mid-range unit with a small name on it. In some cases, they may even be identical, built in the same factory and all, just a different name and a different price. But there are no high-end no-name units. Since you are looking for fairly basic equipment, certainly don't thumb your nose at a contractor that wants to bid on the job with a brand you haven't heard of. Bring the bid info to us (minus the price, of course) and we'll give you the scoop. If you can get the same equipment for less by sacrificing what name gets stamped on the side, why not?

    My point in telling you all of this is that it's hard to know if you're comparing apples to apples. The name on the unit certainly isn't the most important factor, though; the quality and technical correctness of the installation is critical. Worry first about finding a contractor that knows his stuff and that will actually do things correctly, and let brand be secondary.

    If it's any consolation, out of the two HVAC jobs I've had bids on, there was actually quite a lot of variation in installed prices quoted, even among quality contractors quoting comparable- sometimes even identical- equipment. Don't freak out on the whole job; if you get lucky your first bidder just bid too high, and you'll get bids from other competent contractors for less.

  6. #6
    Join Date
    Oct 2005
    Location
    Milwaukee WI
    Posts
    3

    Smile

    Thanks wyounger, you are throwing me a little life-line of understanding and I really appreciate it. I'll get some more quotes and the relay the info minus pricing stuff. FWIW you can shoot me a direct email as well if you like.

    Dilbert_Wi

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event