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  1. #1
    Join Date
    Feb 2009
    Posts
    28

    Newbie needs to know which QUIET gas furnace should I get?

    I had a nice long post that just got killed by a browser malfunction, sigh, but I digress. I have a small condo, 850 sq. feet, with a furnace in the living room that is SO loud that I can't hear my TV or myself think, I've lived with it for 4 years and now have the funds to change it out, I know that the return and duct work have a lot to do with the noise, but in my case it is really the cheapo 13 year old furnace, and we will be increasing the size of the return.

    My HVAC guy says I only need a 40,000 BTU unit, and that those do not come in modulating speeds, so should I get a 40,000 BTU Carrier Infinity 96 which is 2 stage or should I get a modulating 60,000 BTU unit like the Rheem Prestige 90 modulating gas furnace, which claims to be the quietest furnace available, even quieter then a refrigerator even when running at 100%? Will the 60k be overkill, cause clicking, lack of enough air etc.? My current furnace is extremely inefficient so even if I lose efficiency with a modulating furnace I don't care since it will still be cheaper then what I am paying and I am more interested in reducing noise and maintaining a constant temperature.

    I really am looking for the QUIETEST furnace available, period, I will get a steam humidifier to go along with it since those are silent from what I understand, the HVAC guy also suggested lifting the unit off the floor to make it even quieter, I am not sure what that would do but am all for it to reduce noise.

    Any ideas, recommendations, schooling appreciated.

  2. #2
    Join Date
    Sep 2003
    Posts
    1,677
    What part of the country are you in?

    Could you do a heat pump with a gas furnace as a back up. Or a heat pump with electric resistance heat as emergency heat?

    Whatever gas furnace you do decide on make sure it has sealed combustion and that the combustion air comes from the outside directly to the furnace.

  3. #3
    Join Date
    Feb 2009
    Posts
    28
    Quote Originally Posted by small change View Post
    What part of the country are you in?

    Could you do a heat pump with a gas furnace as a back up. Or a heat pump with electric resistance heat as emergency heat?

    Whatever gas furnace you do decide on make sure it has sealed combustion and that the combustion air comes from the outside directly to the furnace.
    I am in Chicago, a heat pump? I would still need the quietest, insulated blower available I guess, haven't looked into that since the AC unit is actually only 4 years old.

  4. #4
    Join Date
    Nov 2005
    Posts
    1,350
    How many supply airs do you have in your condo?
    Do you know the tonnage of the blower you need?
    I STARTED WITH NOTHING, AND I STILL HAVE MOST OF IT!

  5. #5
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,473
    If you only need 40K, I'd get the 2 stage Carrier rather than oversize 50% to get the Mod. I really ought to have a 40K in my little house but smallest I could get in the brand I wanted was 60K so I went that route. I have a toggle switch that can shut off high fire if I want to even if the stat wants it. On high, due to the duct system, things get pretty noisy. Only use it if I need a fast warmup in bitter weather.

  6. #6
    Join Date
    Aug 2007
    Location
    MN
    Posts
    2,677
    If your return comes straight off of the blower cabinet, with no duct to speak of(just a sleeve and register) then no matter what you get, you will have some noise. If it is possible to get more ductwork between the blower cabinet and return grille that would help some( go up the wall with the grille if it is now down low) Also insulate all walls and door to the furnace closet. I would go with the Carrier 40K. Main thing is to get a variable speed blower. If your duct system is too small for the furnace though, you will never get away from the noise.
    You can't fix stupid

  7. #7
    Join Date
    Feb 2009
    Posts
    28
    Quote Originally Posted by cmajerus View Post
    If your return comes straight off of the blower cabinet, with no duct to speak of(just a sleeve and register) then no matter what you get, you will have some noise. If it is possible to get more ductwork between the blower cabinet and return grille that would help some( go up the wall with the grille if it is now down low) Also insulate all walls and door to the furnace closet. I would go with the Carrier 40K. Main thing is to get a variable speed blower. If your duct system is too small for the furnace though, you will never get away from the noise.
    I think you've answered my question for me, that's why he wants to lift the furnace up, so that we can get some ductwork between the blower cabinet and return grill because right now it's just a sleeve and register. So you all think the carrier makes the most sense? Anyone know how loud it is on the 2nd speed? I REALLY wanted the modulating since it would guarantee a constant temp, it sucks that they don't have 40k. They're all similairly priced.

  8. #8
    Join Date
    Mar 2007
    Location
    Missoula, MT
    Posts
    56
    The Rheem Mod 90 has a lot of adjustment on blower speed and with the matching thermostat will modulate the gas output. I do not have the exact btu output in front of me but I believe that it will go as low as 18,000 btu. When the house is at temp the unit will run at low btu output and low cfm. So even crappy duct work can have low noise out of it. Cooling on the other hand my have more noise.
    The Rheem even thou it is larger will/can have a lower btu output with the matched thermostat.

  9. #9
    Join Date
    Feb 2009
    Posts
    28
    Quote Originally Posted by progressive View Post
    The Rheem Mod 90 has a lot of adjustment on blower speed and with the matching thermostat will modulate the gas output. I do not have the exact btu output in front of me but I believe that it will go as low as 18,000 btu. When the house is at temp the unit will run at low btu output and low cfm. So even crappy duct work can have low noise out of it. Cooling on the other hand my have more noise.
    The Rheem even thou it is larger will/can have a lower btu output with the matched thermostat.
    OK, that answers a big question, but the cooling is going to be on/off again? No way to ramp that down as well to keep a constant temp in the summer? So cooling may have more noise with the 60k unit as opposed to a 40k one?

  10. #10
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    A 2 stage with a good thermostat like the Carrier Infinity or Honeywell IAQ, along with a VS fan running all the time, even a 2 stage furnace should maintain a constant temperature if it's properly sized. I have no noticeable temperature swings with this set-up.

    What climate are you in? With a smaller home, you might find that the payback on a 90%+ furnace over a 80% can be 10 years or more. A 2 stage 80% with a VS fan might be all you need. Combined with a heat pump, you have 3 stages of heat.

    Everyone assume you MUST have a condensing furnace because that's the highest effeciency. But 10% is just that. Only 10%. For some, that might only save $50-60 per year. WIthout giving prices... I'll say that it could take 20 years to recover the cost. Although the next time you repalce the furnace you already have the vent pipes installed.

  11. #11
    Join Date
    Mar 2007
    Location
    Missoula, MT
    Posts
    56
    For A/C the cfm will match the tonage no matter what the heat btu of the furnace. On the mod you can set the cfm exactly what you need to match the A/C unit. If you are tring to minimize the noise also with the A/C then use a 2 stage A/C then the mod will stage the blower to 1st and 2nd stage of the A/C low cfm to high cfm.

  12. #12
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Keep in mind that if you go with a 60k BTU furnace, you need to have ductwork sized large enough for 900 CFM. Some condos might only be sized for 800CFM or even less if newer consturction. Possibly only 600CFM. You could end up with a system that's noisy when it goes to high stage.

    Although the fan speed can be adjusted for a higher temeprature rise to match your ductwork, but only to a point.

  13. #13
    Join Date
    Mar 2007
    Location
    Missoula, MT
    Posts
    56
    Whith the Mod the unit will adjust the gas and the fan speed to keep the DELTA T with in the comfort zone so in the heating mode you can adjust the the up or down the temp rise to match the duct work. The unit is designed to run from 500 cfm to 1200 cfm

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