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  1. #40
    Join Date
    Oct 2008
    Location
    Michigan
    Posts
    29
    Based upon my final loss (80K) and load (34K Sensible) numbers and the feedback in this thread I believe the following systems will meet my needs better than the original proposals

    Sys #1 Bryant 355BAV 100K in (not CAV) and 286 4 Ton 16 Seer HP
    Sys #2 York 2 Stage Affinity 100K in and 18 Seer HP (9.8 HSPF is the deciding factor)

    My thanks to all who participated in this thread as it has given me insight into the complexity of selecting the appropriate equipment and ensuring that the contractor I select knows why he is matching a certain furnace with a specific heat pump. It also gave me cause to run my own manual-J (something 3 out of 4 contractors refused to do). I'ts now obvious why pro's should do these calcs before recomending equipment and the need to actually measure the insulation thickness in the walls.

  2. #41
    Join Date
    Jul 2005
    Posts
    24
    Hi:

    Just this month I had a 100Kbtu 80% replaced with a 75Kbtu Rheem mod, model RGJD. What I am reading here is somewhat of a concern. I picked the unit for both efficiency and comfort. Here is what I've observed so far:

    The unit is very comfortable, and most of the time you can hardly hear it. I haven't had it long enough, and the temp is mild enough so far, that I don't have a handle on gas usage.

    I programmed my home automation controller to read the thermostat PWM signal. When bringing up the house in the morning, the T-stat starts at 100% and ramps down to 40% before shutoff. When cycling to maintain temp, it starts at 60% and ramps down to 40% before shutoff.

    Now, my question for Captain CO and RoBoTeq: Do you believe the mod or staged furnaces are less efficient on low-fire due to the furnace itself, or conduction loss in the ductwork because the furnace spends more time on? As an engineer, I'm interested in as much detail as you are comfortable providing.

    Thanks, Larry

  3. #42
    Join Date
    Apr 2008
    Location
    Upstate New York
    Posts
    721
    if these companys selling these units do not tell their customers that these are 50% efficient running at low stage I would think they can be held liable.

    Mine always fires and runs at low UNLESS it has to raise the temp more han 2 degs which the only time it does this is after a setback of 5 degs at night. Then it goes to high.

    I have only had it 3 months so not an real cold weather yet but im thinking of calling the company Monday now that I hear this stuff. I went from a 105k btu oil furnace to a 60k btu 2 stage and it sounds like I got screwed !

    I cant imange even in the winter this will fire at hi stage when it only has to go up a deg or 2. The temp rise is right wher it should be both hi and low fire

  4. #43
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,764
    Quote Originally Posted by tinknocker service tech View Post
    i may be wrong but i believe they are both stageing furnaces. York just has more stages then the others.

    I believe lennox is the only one that has a true modulating gas valve and the rest are staging.

    like i said i could be wrong
    So the Lennox has infinitely varing manifold pressure?

    At 65 steps, The York modulates.
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  5. #44
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,764
    Quote Originally Posted by Jim Davis View Post
    If you are comfortable having cold air blowing out of your registers and the highest gas bill on the block either one will work.
    Haven't had cold air blowing out the registers of any York mod.(ok, the one that the trap cracked on it did when it went into failure)

    Replaced a 90% (won't mention the brand)with a York 95% mod, and his gas bill is lower. And his house has a more even temp through out.
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  6. #45
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,764
    Quote Originally Posted by cpetku View Post
    Would a typical installer setup the system, for GAS heat only in the high stage assuming the outside temp has already passed the need for 30KBTUh?

    One of the concerns I had was when the system changes over to Gas, will the furnace start at low fire and take awhile to figure out it really needs to be medium or high....

    Also, since the Sales people who have sent quotes don't really beleive in Manual J I did my own 36K gain / 88K loss Should I expect the HP to be sized higher than 3 Ton?
    No, the HP's BTU output will be less then the furnaces low fire output at the switch over point. So the furnace sarting in low fire is still going ot be able to heat the house at balance point.

    What was the sensible and latent load, and what were the design temps you used.
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  7. #46
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,764
    [QUOTE=cpetku;2008275]Based upon my final loss (80K) and load (34K Sensible) numbers and the feedback in this thread I believe the following systems will meet my needs better than the original proposals

    Sys #1 Bryant 355BAV 100K in (not CAV) and 286 4 Ton 16 Seer HP
    Sys #2 York 2 Stage Affinity 100K in and 18 Seer HP (9.8 HSPF is the deciding factor)

    QUOTE]

    Are you really looking at the Affinity YZH, or the Affinity YZE heat pump.
    You won't get a return on the YZH over the YZE.
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  8. #47
    Join Date
    Apr 2008
    Location
    Upstate New York
    Posts
    721
    beenthere, whats your view point on this ? Is my Rheem RGRL 2 stage really running at less than 50% efficiency in low stage ?? This is where mine runs in this type of weather 98% of the time ?

    If this is the case someone is going to get a knot on their head ! I will have them take it out and put in a single stage if this is right. How do you know for sure what efficiency it is at low fire ?

    This was NEVER explained to me nor have I ever heard this before......

    I feel like I got boned, it seems like a 60K btu for my 1100 sf home is right and every company told me the same thing

  9. #48
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,509
    Quote Originally Posted by cvcman View Post
    if these companys selling these units do not tell their customers that these are 50% efficient running at low stage I would think they can be held liable.

    Mine always fires and runs at low UNLESS it has to raise the temp more han 2 degs which the only time it does this is after a setback of 5 degs at night. Then it goes to high.

    I have only had it 3 months so not an real cold weather yet but im thinking of calling the company Monday now that I hear this stuff. I went from a 105k btu oil furnace to a 60k btu 2 stage and it sounds like I got screwed !

    I cant imange even in the winter this will fire at hi stage when it only has to go up a deg or 2. The temp rise is right wher it should be both hi and low fire


    Just because your oil fired furnace was rated for 105.000 btu does not mean it was fireing at that. It is not uncommon for an oil burner to be down rate and may have been fireing at 80,000 btu
    you load calc may ave come to 60,000 btu total.
    i dout very much you git screwed. The unit is handling the load it is under and in low fire now as the load increases it will go to high or low depending on set up.
    sounds like it is doing what it is designed to do
    see how things go first

  10. #49
    Join Date
    Apr 2008
    Location
    Upstate New York
    Posts
    721
    it already seems as though with only about 15 cycles of 10 mins each it has used 3 therms of gas. At this rate if it fires 2 cycles per hour in cold weather for a 24 hr period I will use 460.00 a month in gas !

    Thats HUGE for a 1100 sf house. Also WHY would I want a furnace that is supposed to be very efficent but it runs most of the time at low stage and I am told here low stage is less than 50% efficient, I got boned !

  11. #50
    Join Date
    Jul 2006
    Location
    NW burbs of Detroit
    Posts
    6,058
    Quote Originally Posted by cvcman View Post

    beenthere ......

    I feel like I got boned, it seems like a 60K btu for my 1100 sf home is right and every company told me the same thing
    Went back stage afterall?

  12. #51
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,764
    Quote Originally Posted by cvcman View Post
    it already seems as though with only about 15 cycles of 10 mins each it has used 3 therms of gas. At this rate if it fires 2 cycles per hour in cold weather for a 24 hr period I will use 460.00 a month in gas !
    A 60,000 BTU input furnace, would have to run for 5 hours to use 3 therms.

    So either it ran a lot more then 15 cycles of 10 minutes (which would only be 2.5 hours) cycles, or you have a gas leak, or other appliance using gas.

    Being yours is 60,000 BTUs, it would have to run 8.3 hours in first stage to use 3 therms.
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  13. #52
    Join Date
    Aug 2002
    Location
    Westlake, Ohio
    Posts
    2,461
    Quote Originally Posted by larryb View Post
    Hi:

    Just this month I had a 100Kbtu 80% replaced with a 75Kbtu Rheem mod, model RGJD. What I am reading here is somewhat of a concern. I picked the unit for both efficiency and comfort. Here is what I've observed so far:

    The unit is very comfortable, and most of the time you can hardly hear it. I haven't had it long enough, and the temp is mild enough so far, that I don't have a handle on gas usage.

    I programmed my home automation controller to read the thermostat PWM signal. When bringing up the house in the morning, the T-stat starts at 100% and ramps down to 40% before shutoff. When cycling to maintain temp, it starts at 60% and ramps down to 40% before shutoff.

    Now, my question for Captain CO and RoBoTeq: Do you believe the mod or staged furnaces are less efficient on low-fire due to the furnace itself, or conduction loss in the ductwork because the furnace spends more time on? As an engineer, I'm interested in as much detail as you are comfortable providing.

    Thanks, Larry
    Good I know you might undertand this. Burners heat heat exchangers. 60% of the heat generated is by radiant heat. If you reduce the flame size the flame is farther from the heat exchanger and makes the heat exchanger less hot. No different than moving your hand away from a candle flame. Therefore the efficiency of heat transfer is greatly reduced. Then the rest of the heat exchanger has to be scrubbed with the gasses produced by combustion. It is hard to scrub a 100,000 btu heat exchanger with 60,000 btus. It would be like putting a 2-cylinder engine in a van and expecting to get better milage because you drive slow. The weight of the van doesn't change.
    captain CO

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