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  1. #1
    Join Date
    Feb 2012
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    Temperature can't reach set point

    Hi:

    A few weeks ago, I noticed that the temperature in the home (as reported by the thermostat) often does not come up to what we've set it to. Typically, we set it to 22C (71.6F), but it often only makes it as high as 21C.

    I have a heat pump (York YZE series) with a natural gas furnace (York YP9C) as the backup. However, during winter months I typically set the thermostat to "EM Heat" in order to use only the gas furnace.

    When I first noticed and tried diagnosing the problem, the temperature was set to 24C, but could only seem to make it up to 21C. As a test, I decided to try switching to the regular heat mode and then checked outside to make sure the heat pump had come on... it had. After a while the temperature managed to get up to 22C, but couldn't seem to make it any higher. A little while later, I also noticed a fairly loud rumbling coming from the furnace so went down to check it out. The 3/8 liquid line was quite hot to the touch, only a bit cooler than the 5/8 gas line. As I was growing increasingly concerned that this was quite abnormal, I decided to switch back to EM only (at least the furnace didn't sound like it would tear itself apart that way) and called the technician the next day.

    When he came out, he spent 3 hours fiddling about and ultimately decided that the filter needed replacing and that I should remove the thin dust register filters I had installed throughout the house. The filter we use claims to be good for a year, but I nevertheless changed it and clearer the registers and opened them all fully (some were partial to help adjust temp in diff rooms). As I expected, nothing has changed.

    In discussing with the technician, he felt that the symptoms suggested that not enough air was flowing through the system and so was leading to not moving enough heat out of the furnace. This made sense enough to me, but when I asked about the blower or perhaps the blower control system being the problem he dismissed the idea... something about "those boards rarely fail like that". It almost seemed like it was too hard, so he couldn't be bothered (or perhaps didn't know how) to troubleshoot that type of issue.

    I'm now at the point where I'd like to run some additional tests myself to try and narrow down the problem before getting someone to come out again. Anyone have any thoughts? Oh yeah, could the thermostat be at fault in some way? It isn't all that clear to me how the thermostat controls the fan.

    Thanks,
    Pab

  2. #2
    Join Date
    Jan 2004
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    Lancaster PA
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    67,755
    Full model number of the heat pump and of the furnace would help. Also, what MERV air filter are you using?

    The thermostat doesn't control fan speed.

    Could be the board isn't set up proper for air flow.
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  3. #3
    Join Date
    Feb 2012
    Location
    Atlantic Canada
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    Thanks for the interest.

    Furnace: York YP9C060B12MP11A
    Heat Pump: York YZE03611D

    The filter I replaced was a Healthy Climate MERV 16 (16x25x5). The new filter I decided to try is a Filtrete by 3M (16x25x4), but I can't find a MERV rating on it.

  4. #4
    Join Date
    Feb 2011
    Location
    North East Ohio
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    769
    What are your outside temps lately? Do you have a communicating thermostat? Did the tech see any fault codes on the furnace board? What happens if you remove the filter for a few hours? That is a good way to try and rule out a filter cutting down airflow. 5/8 seems a little small for a 3 TON heat pump. Do you have any issues with A/C in warmer weather?

  5. #5
    Join Date
    Jan 2004
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    Lancaster PA
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    As an experiment. Pull your media air filter. Put in a see through fiber glass one. And then see if it can bring the house up to temp. If it can, then its the air filter, or your duct work is too small for the type air filters you want to use.
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  6. #6
    Join Date
    Jul 2004
    Location
    Massachusetts
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    Unbelievable. Call another contractor or at least the place of business of the first and ask to have someone come out who knows how to troubleshoot a system. The tech should be able to provide you with the following information regardless of what filters you have in place:

    RAT, SAT, TR, RASP, SASP, TASP. He should also do a CFM calculation based on the TR and clock the gas meter to determine that the gas flow matches the furnace rating. If the gas flow doesn't match, then he needs to put a manometer on the incoming gas and gas manifold pressure to determine that he has proper gas pressure.

    The HP is only going to provide the Btus it is capable of producing, dependent on outside air temp. When the OAT get down below about +3C, the output of a properly sized HP will be insufficient to heat the house to set-point. Because of the location of the indoor coil, the HP and gas furnace should not be operating simultaneously and for that reason, it is common practice to have the HP disabled in colder weather. If yours is not, I'd suggest it isn't set up properly. However, I suspect that's a secondary issue. The main issue is to be revealed when the data suggested above has been collected and analyzed.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  7. #7
    Join Date
    Feb 2012
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    Atlantic Canada
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    Quote Originally Posted by NCHeat View Post
    What are your outside temps lately? Do you have a communicating thermostat? Did the tech see any fault codes on the furnace board? What happens if you remove the filter for a few hours? That is a good way to try and rule out a filter cutting down airflow. 5/8 seems a little small for a 3 TON heat pump. Do you have any issues with A/C in warmer weather?
    Sorry, I forgot to mention that the problem is most noticeable when outside temp is colder. The day I was talking about was in the -15C to -20C range. For example, today the outside temp was -7C and the furnace ("EM Heat" mode) seemed reach its set temperature of 24C.

    I don't think he saw any fault codes. While he was here, he tried running it without any filter and he did measure an increase in air flow at the registers. However, temp that day wasn't that cold as I recall. I'll try removing the filter next cold day we have, but am not sure what that will accomplish. This is our 3rd winter with the furnace and have always had the MERV16 filter (with register filters) in place and this is the first year I notice the problem.

    No, I've never noticed the heat pump have a cooling problem in the summer. I'll keep a close eye on that next summer then. How large do you expect the gas line to be?

  8. #8
    Join Date
    Feb 2012
    Location
    Atlantic Canada
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    6
    Quote Originally Posted by skippedover View Post
    The tech should be able to provide you with the following information regardless of what filters you have in place:

    RAT, SAT, TR, RASP, SASP, TASP. He should also do a CFM calculation based on the TR and clock the gas meter to determine that the gas flow matches the furnace rating. If the gas flow doesn't match, then he needs to put a manometer on the incoming gas and gas manifold pressure to determine that he has proper gas pressure.
    I don't know what those acronyms stand for. He did do an airflow measurement at the register nearest the thermostat and showed me that the output dropped by about a third (I think) when the register filter was in place. He also measured the air temperature coming out of the register and seemed to think it was normal (120F?).

    As I've said, what is bothering me in all this is that the filters (register and furnace) have never been a problem before and this is our 3rd winter. What's more is that it appears to be a somewhat intermittent problem.

    I see from the Weather Network that it is currently -20C. The thermostat had reached its set point of 22C this morning. I have just bumped it up to 24C (about 10 minutes ago) and am waiting to see if it makes it there. It first decreased to 21.5C before returning to 22C where it is now. I'll report back once it settles.

    Quote Originally Posted by skippedover View Post
    The HP is only going to provide the Btus it is capable of producing, dependent on outside air temp. When the OAT get down below about +3C, the output of a properly sized HP will be insufficient to heat the house to set-point. Because of the location of the indoor coil, the HP and gas furnace should not be operating simultaneously and for that reason, it is common practice to have the HP disabled in colder weather. If yours is not, I'd suggest it isn't set up properly. However, I suspect that's a secondary issue. The main issue is to be revealed when the data suggested above has been collected and analyzed.
    I thought I read that the newer HP's were capable of extracting heat from the air at even lower temperatures than that now. Since this has all started I have been trying the HP more than I ever have in winter and have been surprised that it manages to warm the house temperature more than the natural gas furnace by about 1C extra. That said, I don't think I consider that normal... seems like the nat gas should make an easier time of it. And then there was the whole rumbling and hot liquid line thing I mentioned in the original post.

    Anyway, thanks so far to everyone for your interest and help. It is appreciated.

  9. #9
    Join Date
    Nov 2006
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    Athens, Ohio
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    If my interpretation of the model number is correct, then the furnace is 60,000 Btu input. Is it possible it is too small for your house?
    Were past winters not as cold? It seems that the furnace can't keep up when the temperature outside falls below a certain point. That would indicate the furnace is undersized.

    I also question the use of a 5/8" suction line on a 3 ton heat pump but that has nothing to do with the inability of the furnace to keep up with demand.

  10. #10
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    Jul 2004
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    Quote Originally Posted by pablito View Post
    I don't know what those acronyms stand for. He did do an airflow measurement at the register nearest the thermostat and showed me that the output dropped by about a third (I think) when the register filter was in place. He also measured the air temperature coming out of the register and seemed to think it was normal (120F?).

    You don't need to know what the abbreviations represent but your technician should and should be able to provide all those numbers. As I stated, those numbers will reveal where the problem lays.

    As I've said, what is bothering me in all this is that the filters (register and furnace) have never been a problem before and this is our 3rd winter. What's more is that it appears to be a somewhat intermittent problem.

    There are many issues that can create this problem. For example, if the gas supply to the furnace isn't adequate all the or intermittently, then you could experience a lack of heat from the furnace. That's just one example of how a technician with proper tools and diagnostic capabilities can locate a problem, while another just keeps guessing.

    I see from the Weather Network that it is currently -20C. The thermostat had reached its set point of 22C this morning. I have just bumped it up to 24C (about 10 minutes ago) and am waiting to see if it makes it there. It first decreased to 21.5C before returning to 22C where it is now. I'll report back once it settles.


    I thought I read that the newer HP's were capable of extracting heat from the air at even lower temperatures than that now. Since this has all started I have been trying the HP more than I ever have in winter and have been surprised that it manages to warm the house temperature more than the natural gas furnace by about 1C extra. That said, I don't think I consider that normal... seems like the nat gas should make an easier time of it. And then there was the whole rumbling and hot liquid line thing I mentioned in the original post.

    Anyway, thanks so far to everyone for your interest and help. It is appreciated.
    I'm not sure you understand how a HP works. Yes, the HP can produce useful heat down to very cold outdoor temperatures but that's not necessarily going to heat your home. HP's are rated for Btu output at two specific outdoor temperatures, 47F and 17F. Since the HP is extracting heat from the outdoor air, as it gets colder outdoors, less heat can be extracted. What that means is that a HP that is rated as 36,000 Btu's at 47F, may produce only 19,000 Btu's at 17F and even less at 10F. Your house may need 27,000 Btu's at 47F and the HP will do the job. But as it gets colder outdoors, your house needs MORE heat, while the HP produces LESS heat. Somewhere between 47F and 17F, the output of your HP and the need os your house are exactly the same. That is called the 'balance point'. Below the balance point (temperature), the HP can no longer supply ALL of the Btu's needed to heat your home to set point. So at temps below balance point the house needs supplemental (auxiliary) heat, in your case, your gas furnace.

    Again, since the HP and gas furnace shouldn't operate simultaneously, it is normal to have the HP totally off below balance point temps and use the gas furnace under all conditions of lower temps. If your furnace is unable to keep your t-stat at set-point, then that's a problem with the furnace alone and not the HP. We already know the HP will NOT heat your home to set-point below the balance point.

    Use the abbreviations supplied to force an otherwise short-cutting or inept or lazy tech to provide useful info. Or you may get a tech that gives you blank stares or excuses as to why he can't provide such data. You neither need or want that tech in your home as he/she is not competent.
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  11. #11
    Join Date
    Feb 2012
    Location
    Atlantic Canada
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    6
    Quote Originally Posted by kdean1 View Post
    If my interpretation of the model number is correct, then the furnace is 60,000 Btu input. Is it possible it is too small for your house?
    Were past winters not as cold? It seems that the furnace can't keep up when the temperature outside falls below a certain point. That would indicate the furnace is undersized.

    I also question the use of a 5/8" suction line on a 3 ton heat pump but that has nothing to do with the inability of the furnace to keep up with demand.
    I checked the max input rating on the furnace panel and you're correct, it is 60K BTUH. The max output is 58K BTUH. I sure hope it is not underrated, but can that be confirmed from simple square footage? The house is a simple 2 story layout. The basement and main floor have an identical layout and are about 1100 sq feet a piece. The second floor is 930 sq ft for a total of 3130 sq ft.

    The tech and I discussed the cold and he told me he had checked weatherdatadepot.com and found that overall this winter was milder. That said, I would argue that on average that may be true, but this year has been one for crazy swings from one extreme to the other. One day is +7C and the next is -20C. I think we've seen more extreme days this year than usual.

  12. #12
    Join Date
    Feb 2012
    Location
    Atlantic Canada
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    Quote Originally Posted by skippedover View Post

    Again, since the HP and gas furnace shouldn't operate simultaneously, it is normal to have the HP totally off below balance point temps and use the gas furnace under all conditions of lower temps. If your furnace is unable to keep your t-stat at set-point, then that's a problem with the furnace alone and not the HP. We already know the HP will NOT heat your home to set-point below the balance point.
    I think I'm with you. One follow-up questions then: If I set the thermostat to 'auto' to let it pick whether to use the HP or furnace, will the 'system' (not sure if that would be the board in the furnace or the t-stat itself) make an intelligent decision to stop the HP when below balance and kick off the furnace? Or will the HP just keep trying to attain the set point even though it could not possibly do so?

    So my initial test yesterday contradicted my initial post. After setting the temp from 22C to 24C, it initially decreased to 21.5C and then took about 40 minutes to get to 24C.

    Last night I decided to try and raise the set point to 27C and watched the temperature rise up to 25C at which point the control board on the furnace itself started reporting 5 amber flashes diag light on the control board. From the manual this apparently means:

    "Heating and capacity is reduced due to restriction in the combustion air or vent system. Check for blocked vent/air pipe or clogged condensate drain."

    My question: Is this sort of diag status also flashed when the furnace reaches its max capacity or can this really only indicate that the furnace still has capacity but is unable to push the fumes out the exhaust properly?

    I'll retry this tonight and report back.

    Pab

  13. #13
    Join Date
    Nov 2006
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    Quote Originally Posted by pablito View Post
    I checked the max input rating on the furnace panel and you're correct, it is 60K BTUH. The max output is 58K BTUH. I sure hope it is not underrated, but can that be confirmed from simple square footage? The house is a simple 2 story layout. The basement and main floor have an identical layout and are about 1100 sq feet a piece. The second floor is 930 sq ft for a total of 3130 sq ft.

    The tech and I discussed the cold and he told me he had checked weatherdatadepot.com and found that overall this winter was milder. That said, I would argue that on average that may be true, but this year has been one for crazy swings from one extreme to the other. One day is +7C and the next is -20C. I think we've seen more extreme days this year than usual.
    Square footage is only one factor in the proper sizing of a furnace. Do you know if the installing contractor calculated the load for the house? That is the only reliable method to determine the correct size. "Rule-of-thumb" is not a reliable calculation method.

    I see from another post that your furnace shuts down with an accompanying error message. That needs to be resolved as it may explain why it can't get up to temperature.

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