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  1. #1
    Join Date
    Jun 2005
    Location
    Fort Collins, CO
    Posts
    3
    I have several questions concerning the bids I got to replace our 27 year-old funace/ac. This is a pretty difficult task since these units are still operating.

    First, let me say I asked as many people as I know for references on installers, and have confidence in all the installers.

    House specs to keep in mind. 2600 sq. ft. 600 in the basement. Tri-level construction with 3 bedrooms upstars. A fireplace on the middle level that we still use in the winter mainly because that room (family room) is soo cold.

    1) should I replace now or wait until they completely fail!!

    2) I want to put in a 2-stage, variable speed unit because the tri-level is a bugger to keep warm everywhere, but I'm not sure about the high efficiency units.. The install cost is is quite different. Our winters are pretty mild. Maybe 10 days are cold, <20F all day. I'm leaning toward the 80%.. Should I look harder at the 90+% units?

    So far I have quotes from Trane (2), Bryant, Lennox. Tomorrow I have a Rheem dealer giving me a quote. What are the differences in these furnaces?
    Also is the VS option worth the price tag?

    3) Is it necessary as one of the contractors has mentioned to have a 2-stage thermostat? I currently have a digital/programmable thermostat. Should I replace it with a special thermostat for the 2-stage VS unit?

    4) I'm trying to stay in a budget. We use the AC maybe 30 days a year. Should I replace the AC? The city is offering a $300 Rebate for 13-seer and better.
    Should this be a consideration given my usage?

    4a) If so, should I match the systems? The reason I ask is one of the bids offered a 13-seer system for about $800 less than just about everyone (evem for the same unit), but it is an R-22 Goodman model that from what I can tell is going to go away next model year. It would be installed with a lennox funace. The matched brands are quite a bit more adding more cost to the job (note the next question about tonnage).

    4b) All of the contractors have done load calculations and I let them take their time. Some recommend 2.5 Tons and others 3 Tons for the AC. What are the potential pit falls? Note I have no west windows!

    4c) One contractor was going to up the size of the coil to 3 ton and us a 2.5 ton unit? What are the pitfalls?

    My take on all of what I have read is that the VS is worth the money, and that I should get the most efficient (highest Seer) A/C for the $. Am I off base on this?
    I'm open to any comments.

    Also, It seems that all the equiptment (furnace and A/C) is very good if it is installed properly. My problem is that I have a low bid for a 80% 2-stage VS, w/humidifier matched with another brand 2.5 ton/3 ton coil. The other bids with comparable, though matched equiptment are considerably more. Should this low bid be questioned? How? What corners could have been cut to make the bid considerably lower? What are the right questions to ask?

    Thanks!!!

    [Edited by fortfun on 06-08-2005 at 12:44 AM]

  2. #2
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,178
    1. You are on borrowed time. I'd replace now so it doesn't quit in a heat wave leaving you hot for days.

    2. In a mild climate, 80s may be the best bet though the price of gas is sure climbing so long term, a 90 could pay.

    Everyone has their own opinion on brands. Look for a premium model from whatever brand and pick a good installer.

    Variable speed adds to comfort and efficiency. If budget permits, is a nice addition.

    3. I firmly believe a 2 stage furnace needs a 2 stage stat for full benefit & comfort.

    4. In a mild climate, high SEER cooling probably won't pay. With 30 days of cooling, especially if your juice rates are reasonable, 10 SEER is all that has economic payback. You'll have to do the math. The $300 rebate sure cuts the price of high SEER but if you only save $20-25 a year, still may not be enough.

    We've installed dual brand systems in the past, including my own. As long as the indoor coil matches the outdoor unit, it works fine. If looking for high SEER, you won't get a rating with 2 brands.

    Oversizing reduces humidity control in mild weather due to short run times. Larger coils can too but sometimes that's what the manufacturer calls for.

    Low bids can mean not doing stuff others are doing. Check the proposal carefully. Not changing the lineset, disconnect, stat, less metal work, skipping chimney liner if needed...

    http://www.johnmills.net/work/advice.html
    http://www.johnmills.net/compare/outdoorunits.htm
    http://www.johnmills.net/compare/compare90.htm


  3. #3
    Join Date
    Jun 2005
    Location
    Fort Collins, CO
    Posts
    3
    BaldLoonie,

    Thank you for answering my questions. I feel better now about what questions to ask as I work my way through the work proposals I have received. I must say, I have learned a lot about HVAC in the last week or so, probably more than I would have liked to. This forum is great.. lots of good questions and great answers...


  4. #4
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    Baldy covered it well. I just want to expand on one topic.

    I want to put in a 2-stage, variable speed unit because the tri-level is a bugger to keep warm everywhere,

    Ignore me if Im taking this in the wrong direction. But it seems to me that youre saying you have a hard time heating the place evenly. Im assuming its hard to heat the lowest level and not overheat the highest level.

    IF Im reading that right, high efficiency equipment hasnt got poop to do with getting the levels to even out**. An 80+ builder model with a 10 SEER AC will have (almost) the same exact problem with unevenness as a 90+ VS model with a 19 SEER AC. A heater and air conditioner does nothing more than put out conditioned air. They have not one thing to do with where it goes. Trick duct design and the possible addition of a zone system are what you need to be thinking about.

    **Well... they are relevant in the sense that higher end equipment has staged heating and cooling which is extremely useful if you install a zone system. But in the end the evenness of the house temps will rely on duct design, diffuser selection, air circulation, etc.

  5. #5
    Join Date
    Jun 2005
    Location
    Fort Collins, CO
    Posts
    3
    Irascible,

    You are correct that the lower level is the problem, at least in the winter. This is the result of 1) being on a slab and 2) registers coming out of the ceiling. I guess what I have been reading and told to a lesser extent that the two stage furnace with a variable motor will circulate more air. This will result in more even temperatures. Of course, I'm being somewhat realistic.. It will likely help but not solve this problem. I also have a wood insert on the lowest level that we use quite often...(messy!). I'm hoping that I can use it less.

    On a related issue, I am going to have some duct work done to help with air flow. The system branches to 1)the upstairs (floor) and lowest level (ceiling)and 2) the middle level. At the end of the mid-level branch two registers go out the end. I'm going to have those registers moved to the side and block of the end.

    From what you are saying other things can be done. What is trick duct design? I don't think zoned heat is within my budget? I have a father-in-law that was a mechanic at Kodac for 30 years who is really good with fittings/sheet metal etc.. Could his expertise be useful?


  6. #6
    Join Date
    Mar 2002
    Location
    Concord, CA
    Posts
    2,635
    All I mean by trick duct design is duct design done right. Doing ducts correctly on a zone system... THAT'S a trick few contractors pull off.

    I doubt a higher volume of air is going to help much. If the variable's extra blowing capacity pushes more air, it will push more to all three levels. Oversizing a standard (cheaper) blower by one ton will usually have the same effect so long as your ducts aren't too terribly small. And if they are terribly small then you may not want to buy a VS motor. A standard motor's amp draw goes down when you choke it for air. A VS motor's amp draw goes up. If it's forced to run flat out just to compensate for terribly undersized ducts then it will run hotter and not last as long (specifically the motor controller might go bad after a few to ten years).

    Be very weary of contractors who believe variables are a cure all for airflow problems. They're almost always wrong.

    What can theoretically be of help is running the fan 24/7. Constantly mixing the air can be useful, though in my experience the benefit is often negligible. A VS motor is useful for that purpose because when the thermostat asks for fan only it will run at a fairly slow speed (not flat out) and may use the electricity of one or two light bulbs - which is a lot less than a standard blower.

    You'd have to ask your father-in-law that question. If he knows duct design and installation then he knows that he knows it.

  7. #7
    Join Date
    Sep 2004
    Posts
    3,157
    On a related issue, I am going to have some duct work done to help with air flow. The system branches to 1)the upstairs (floor) and lowest level (ceiling)and 2) the middle level. At the end of the mid-level branch two registers go out the end. I'm going to have those registers moved to the side and block of the end.


    As stated before " a zoned system would be the way to go "

    something I dont understand is that if you are planning on doing the modifications to your ductwork as stated above, why not put zones in instead

  8. #8
    Join Date
    Feb 2004
    Location
    Tucson AZ
    Posts
    55

    consider duel fuel

    I don't know where you live or what your utility rates are but where I live natural gas runs around $1.00 per therm and electricity runs just under $.10 per KW (winter rates are even lower). I am also in a mild climate. I switched to a Duel fuel heat pump system last winter my system is set to switch from heat pump to gas furnace at a 35 degree outdoor temperature. I cut my heating cost by about $100.00 per month over the two-three months that we needed heating. I don't know if the contractors in your area are familiar with this type of a system but they are gaining popularity due to the rising cost of fossil fuels.

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