Hello folks, I'm working with a local pro but I'm having a hard time describing an issue and 1st round of troubleshooting hasn't worked.
Issue: Ruud forced Achiever 90+ forced air propane-fed furnace (with cooling coil heat pump) in attic of single level 1500sqft house, prob 12hrs old, started making faint rumbling noises in Mid Jan this year. Seems related to struggling for airflow in ducting on inlet side around air fiter.
The unit has a Trion air-bear 25x25x5 large air filter in the ducting adjacent to it which I install only real Trion MERV 8 filters into. Note I've had to replace the filters no more than every 4 months because I notice airflow drops dramatically (20-30% of normal) to the point the flow reduction is noticeable and the system will take took long to meet temp demand on either the heating or cooling side, depending on season.
This Jan when the rumbling started and I found it was the furnace, I changed out the filter which was 4mo old on 1/18/21 for a new one and the rumbling stopped. I should note that when the rumbling happens, the unit doesn't behave normally.
Normal operation is tstat calls for heat, relays click, mechanical whirring starts in furnace is heard and within around 10 seconds the burner kicks on (can see blue flame through observation window) and about 15-20 seconds after that, blower kicks on and hot air flows through vents as it should.
When the rumbling noise is heard, the burner flame kicks in reaaalllly late. I don't see it for minutes. It finally kicks on, runs for a short time and then furnace shuts down. The furnace short cycles and tries to make heat but takes several cycles and many minutes to finally satisfy call for heat.
On 2/22/21 the rumbling returned and the furnace was short cycling and struggling noticably trying to satsify call for heat.
I called my trusted local HVAC servicer and he sent a younger tech over who could find nothing wrong with the system, did basic maintenance on it (I told him about the filter etc). He thought the furnace is just getting old and rumbling is just loose panels etc.
After he left the system if anything was slightly louder than before where the rumbling vibrated the house slightly and remained that way for a day. Unhappy with the noiser system, I raised the Tstat, went into attic and no burner flame, rumbing noises etc as before.
I had the wife put her hand near a vent when the blower kicked on and very little airflow. So I pulled the cover off of the air bear filter housing and WHOOSH a bunch of airflow and the wife said more air coming from vent. I tried to pull the filter out with system running (which I've occasionally done easily in the past) and I couldn't budge it. Too much pressure drop across it. After a bit of struggling, filter was slowly removed and hot air blowing like gangbusters.
I look at the 1 month old MERV 8 filter just removed and I pulled out new one (from a new shipment/box) and they looked the same, both real Trion MERV 8, bla bla bla. Put in the new filter and the furnace is happy again.
Not an expert here but system is acting like it's starving for air and I'm going through $25 air filters practically monthly now. What gives? It seems like I must either replace the filters monthly or try a different filter setup which has less pressure drop. But this system ran fine for years, albeit the ducting may be slightly undersized, that filter 25x25x5 should be enough I would think.
Thanks and sorry for the wall of text.
Issue: Ruud forced Achiever 90+ forced air propane-fed furnace (with cooling coil heat pump) in attic of single level 1500sqft house, prob 12hrs old, started making faint rumbling noises in Mid Jan this year. Seems related to struggling for airflow in ducting on inlet side around air fiter.
The unit has a Trion air-bear 25x25x5 large air filter in the ducting adjacent to it which I install only real Trion MERV 8 filters into. Note I've had to replace the filters no more than every 4 months because I notice airflow drops dramatically (20-30% of normal) to the point the flow reduction is noticeable and the system will take took long to meet temp demand on either the heating or cooling side, depending on season.
This Jan when the rumbling started and I found it was the furnace, I changed out the filter which was 4mo old on 1/18/21 for a new one and the rumbling stopped. I should note that when the rumbling happens, the unit doesn't behave normally.
Normal operation is tstat calls for heat, relays click, mechanical whirring starts in furnace is heard and within around 10 seconds the burner kicks on (can see blue flame through observation window) and about 15-20 seconds after that, blower kicks on and hot air flows through vents as it should.
When the rumbling noise is heard, the burner flame kicks in reaaalllly late. I don't see it for minutes. It finally kicks on, runs for a short time and then furnace shuts down. The furnace short cycles and tries to make heat but takes several cycles and many minutes to finally satisfy call for heat.
On 2/22/21 the rumbling returned and the furnace was short cycling and struggling noticably trying to satsify call for heat.
I called my trusted local HVAC servicer and he sent a younger tech over who could find nothing wrong with the system, did basic maintenance on it (I told him about the filter etc). He thought the furnace is just getting old and rumbling is just loose panels etc.
After he left the system if anything was slightly louder than before where the rumbling vibrated the house slightly and remained that way for a day. Unhappy with the noiser system, I raised the Tstat, went into attic and no burner flame, rumbing noises etc as before.
I had the wife put her hand near a vent when the blower kicked on and very little airflow. So I pulled the cover off of the air bear filter housing and WHOOSH a bunch of airflow and the wife said more air coming from vent. I tried to pull the filter out with system running (which I've occasionally done easily in the past) and I couldn't budge it. Too much pressure drop across it. After a bit of struggling, filter was slowly removed and hot air blowing like gangbusters.
I look at the 1 month old MERV 8 filter just removed and I pulled out new one (from a new shipment/box) and they looked the same, both real Trion MERV 8, bla bla bla. Put in the new filter and the furnace is happy again.
Not an expert here but system is acting like it's starving for air and I'm going through $25 air filters practically monthly now. What gives? It seems like I must either replace the filters monthly or try a different filter setup which has less pressure drop. But this system ran fine for years, albeit the ducting may be slightly undersized, that filter 25x25x5 should be enough I would think.
Thanks and sorry for the wall of text.
source https://hvac-talk.com/vbb/threads/2227012-Ruud-Furnace-struggling-for-airflow?goto=newpost
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