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  1. #1
    Join Date
    Nov 2012
    Posts
    9

    Furnace: Hissing Noise and Little to No Warm Air?

    Hello, I hope I am in the correct forum here. I am not here for DIY info, as I can see is against the rules, because I live in a rental property and maintaining the furnace/ac is not my responsibility. However, my property manager insists my furnace is working as designed and will not have it looked at. She insists that the maintenance man(supervisor?) just needs to come out and explain the way the furnace works. Before I get in to details here is some pictures of the unit and some information:
    Model Number and Tech Info
    http://i.imgur.com/Yg3gh.jpg
    Picture of the unit:
    http://i.imgur.com/Q2JTQ.jpg

    I called the property manager about 2 weeks ago to report a number of issues that sprung up at once. I said the furnace seems to be running much harder then it should be. However, some times it may only kick on for 15 seconds, kick off. Then 5 min latter, kick on for 15 seconds, then kick off for another 5 min, and may repeat this a few times in an hour. Most of the time it is putting out room temp and at times even cold air. The other thing I noted is that most of the time, when the furnace is about to shut off, it makes a sort of hissing noise. The way I describe it to people is that it sounds like an air valve popping off similar to air brakes on a semi when they blow off excess air. She insists that these units are, more or less, unconventional and do not need to put out warm air to actually heat our town house.

    Anyway, I hope I have kept this short but detailed. Is it time to call an HVAC repair man and send the property manager the bill?

  2. #2
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,773
    When is the last time the air filter was changed. may also have a dirty indoor coil.
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    How many times must one fix something before it is fixed?

  3. #3
    Join Date
    Nov 2012
    Posts
    9
    Quote Originally Posted by beenthere View Post
    When is the last time the air filter was changed. may also have a dirty indoor coil.
    Thanks for the prompt reply! We moved in here mid June or July, so possibly around that time, but given we had no working smoke detectors when we moved in, I wouldn't be surprised if it was long before that as I am getting the impression they perform no routine maintenance here.

    One thing I was unclear about, but would like additional feedback on the notion that the furnace can heat our unit with out actually putting out warm air. I have no knowledge of HVAC at all, and will not pretend to. However, it seems like basic logic that the furnace has to put out warm air to keep the unit at the set temperature. Logic aside, the furnace *is* keeping our unit heated properly even when we had a ~5MM gap in one of our windows letting cold air in.

  4. #4
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,773
    I believe you have a heat pump. Older ones don't put out real warm air. if its just straight electric resistant heat, it may be a smaller strip heater, and the air won't feel real warm.
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    How many times must one fix something before it is fixed?

  5. #5
    Join Date
    May 2000
    Location
    Rochester, NY, USA
    Posts
    14,497
    clogged filters, dirty coils, undersize unit, the hissing is probably from leaking duct work.
    I only drink a little, but when I do
    I turn into another person and THAT person drinks a lot

  6. #6
    Join Date
    Nov 2012
    Posts
    9
    Quote Originally Posted by beenthere View Post
    I believe you have a heat pump. Older ones don't put out real warm air. if its just straight electric resistant heat, it may be a smaller strip heater, and the air won't feel real warm.
    Thanks for the info beenthere. I like your avatar, even though I am more of a fan of the current Ford and Dodge US cop cars.

    Quote Originally Posted by jmac00 View Post
    clogged filters, dirty coils, undersize unit, the hissing is probably from leaking duct work.
    In regards to the hissing, for what it is worth, the first week or two(maybe longer) we were running the furnace, it did not make this hissing noise. When I tried to tell the property manager this she just started huffing and puffing and insisting nothing was wrong even though she could not explain why the hissing started suddenly.

  7. #7
    Join Date
    May 2000
    Location
    Rochester, NY, USA
    Posts
    14,497
    do you know how to change the filter??? if you do, a new one is $1.50, throw a new one in and see what it sounds like?

    btw, is this hissing sound constant or just when the blower runs? Is it a hissing sound or more like a Buzzing sound?
    I only drink a little, but when I do
    I turn into another person and THAT person drinks a lot

  8. #8
    Join Date
    Nov 2012
    Posts
    9
    Quote Originally Posted by jmac00 View Post
    do you know how to change the filter??? if you do, a new one is $1.50, throw a new one in and see what it sounds like?

    btw, is this hissing sound constant or just when the blower runs? Is it a hissing sound or more like a Buzzing sound?
    Here is a pic of the filter, I couldn't really tell if it was dirty or not.
    http://i.imgur.com/DEDx4.jpg

    As for the hissing, neither. Another reason I compare it to air brakes on a semi is it only happens for a few seconds right before the furnace is about to shut off.

  9. #9
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,773
    Not dirty enough to cuase a problem.

    Its also possible you have straight A/C with electric heat. And the A/C is coming on with the heat is on.
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  10. #10
    Join Date
    Apr 2001
    Location
    Over Here
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    1,105
    Quote Originally Posted by Otis3118 View Post
    it only happens for a few seconds right before the furnace is about to shut off.
    I agree with beenthere... Sounds like refrigerant in the evaporator coils equalizing when the condensing unit cycles off.

    You most likely have cooling and your electric heat strips operating simultaniously. When your thermostat satisfies your call for heat, it is turning them off at the same time. The blower runs for about 2 mins longer than the condenser because the control inside the air handler is designed to do that, hence the sound you are experiencing before it turns off.

    Need to get someone out to verify the wiring is correct, as your electric bill will be higher than it should.

    I could not determine which heater assy your unit has, but I would imagine they are 10 kw which is roughly 34,000 BTU's. The air conditioner that would go with your air handler is either 18,000 or 24,000 BTU's. Operating simultaniously, your heat would cancel your cooling, and provide some heating, but definitely not hot as you have described.

  11. #11
    Join Date
    Nov 2012
    Posts
    9
    Well a little update here, the hissing happened at least twice last night, but the furnace did not shut off right afterwards. It just kept on running. Now for what it's worth, last night was probably the coldest night here so far this year getting down in the mid to upper 20s. Because of this I think we had our thermostat set a bit higher then usual.

    One other thing I forgot to mention, the other day I had played with the thermostat a bit. I noticed if I suddenly turn up the temperature on the thermostat to a dynamic degree, say around 7*F(it's an old analog(?) thermostat with a slider - so I am guessing here) it does put out a more noticeable amount of warm air.

    The later paragraph is making me think it is indeed refrigerant in the evaporator coils based on the information you guys have provided.

  12. #12
    Join Date
    Oct 2010
    Location
    Anderson, South Carolina, United States
    Posts
    7,761
    You have a heat pump with electric resistance back up heat. When you turn the tstat setting up ~2-3F above inside temp the resistance heat comes on to catch up to the new set point so the air is warmer, when it gets to the same temp just the heat pump runs and the air doesn't feel as warm. The hissing noise is a defrost cycle to remove any built up frost or ice from the outdoor units heat transfer coil. In defrost the unit switches from heat mode to cool mode and the resistance heat comes on to temper the cooled air so it doesn't blow really cold air. Maybe the resistance heat is not coming on in defrost thus blowing cool air into the home while in defrost mode. The hissing sound is a normal noise for a heat pump in defrost. Heat pumps only blow out ~90F air when the resistance heat is not on so it does not "feel" very warm but does heat the house. Hope this explanation helps.

  13. #13
    Join Date
    Feb 2012
    Location
    Toronto Canada
    Posts
    1,090
    Buy a Thermometer and tell us what temps you are getting out of your register's. What type of heating did you have in your OLD house before this one?

    JT ^^^^^ Nailed it. Thats what I was thinking. I also don't think you are used to this style of heating

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