ReplyAre the registers in the ceiling? Is that furnace a 2-stage or modulating furnace? Where are the return air grilles?
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Now that the issues are corrected for my main level system, I now have a question about my upstairs HVAC system.
I had a Lennox SL280v gas furnace installed last July. This week has been pretty chilly here in Georgia. We have been having comfort issues in our 3 bedrooms upstairs, and they haven't started yet until the temperatures got pretty cool here outside. The thermostat is located in one of the bedrooms which has high ceilings. The other two bedrooms have standard 8 ft ceilings. I have noticed that the temperature in the room with the high ceilings is always a few degrees warmer than the others. For example, during the afternoon that room was 69*F and the other two rooms were both 64*F. The doors were open all day. Plus, the bedroom with high ceilings has curtains over the window and faces the sun the majority of the day. I would assume that could be part of the cause of the unbalanced temperatures. My son has been complaining that his bedroom has been cold in the afternoon right after he gets home from school. My daughter's room is the room with the high ceilings and her room feels nice. The third bedroom is the guestroom, which is hardly used. We had our attic insulation evaluated last summer and the contractor said that the insulation was all fine. The furnace has also been having very short cycles as well (like in the 3-4 minute range).
What could possibly be a good solution to solve the unbalanced temperatures upstairs? We do plan to have a service tech out soon if this problem continues.
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Are the registers in the ceiling? Is that furnace a 2-stage or modulating furnace? Where are the return air grilles?
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The furnace is 2-stage. The registers are in the ceiling. There are 2 returns in the hallway and there is 1 return in each room.
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Okay, thanks for the infomation. I don't like to use 2-stage equipment in that situation because when the furnace starts on low fire, you'll get a low speed fan (blower) which doesn't make much sense with the registers (high) in the ceiling.
But, that said, I don't understand why the furnace is short cycling so much. You might want to run the blower on constant blower to see if that make a difference.
Also check the filter to make sure it's clean.
God Speed, Jim. We'll miss you - 2-26-23
Thermostat CPH may be set too high. While having the stat in the room with the high ceilings is a good idea for the cooling season. It can give problems in the heating season.
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I replaced the filter over a month ago. We use lower quality pleaded filters because they are better than cheap fiberglass filters in my opinion. Your opinions could be different though. Our old furnace had no problems with it. We just wanted to upgrade to variable speed. I'll see if running the blower in continuous fan speed will help. But I'm just wondering why the furnace has short cycles. It's not set up for two stage, so the furnace will run on low for 7 minutes and then switch to high.Originally Posted by George2
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That could be the issue, but I really don't know. Sometimes we have short cycles in cooling mode as well.
God Speed, Jim. We'll miss you - 2-26-23
Setting the thermostat to a lower CPH for heat, and for cooling may help.
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Thanks beenthere. The Thermostat is a Honeywell RTH6450D just incase that might help.
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I am also wondering if the blower cfm is set too high.
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Upstairs in GA probably requires very little heat. Do you know the BTU of your furnace?
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The furnace is 45,000 BTU input on first stage and 66,000 BTU input on high stage. That's what the service tech said when he came out a few weeks ago for our annual heating inspection and tune-up. The furnace is matched up with a 2 ton Amana Distinctions (Goodman) Air Conditioner that was installed last April along with a new evaporator coil.
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45,000 should be plenty, doubt the 2nd stage will ever kick on.
Does it 'feel' hot when it short cycles?
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Not really, well sometimes. It's kinda hard to explain. There has been some times when I bumped up the temperature a few degrees and the furnace was able to stay on for 7 minutes to allow high stage to kick in. After that it really feels warm.
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turn the fan to on and see if it evens out the temps
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If the house was vacant for an extended period and you wanted a quick warm up the 2nd stage could be useful. For keeping a constant temperature I doubt he 2nd stage would ever be used. Looks like they sized the furnace based on 1st stage capacity with 2nd stage as "reserve/recovery". How much total sqft for the upstairs? Does it feel like it gets hot/cold during normal cycling?
Cycle time is a comfort vs. efficiency game. Setting the thermostat for longer cycles give larger temperature swings which if excessive result in poor comfort. Shorter cycles reduce efficiency and add wear and tear to the unit. Striking a balance is the key. Oversized equipment will make it difficult, undersized equipment won't keep up on the coldest/hottest days. The idea of 2 stage is size it so that the unit won't be able to keep up on 1st stage once temps start getting close to outdoor design temperature.
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catmanacman and 54regcab thanks for the input. The furnace that was installed according to Lennox's website is the smallest capacity SL280v it comes in. The upstairs does get warm during normal cycle, but it takes about 10 to 15 minutes for the temp to cool down. The total sq ft is 1400 sq ft.
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Just in case this helps, here's the model number of the furnace.
I meant to say 43,000 BTU, not 45,000 BTU in one of my previous posts.
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Low BTU furnaces with variable speed blowers have always been difficult to find. The only manufacturer I know of who makes a furnace under 50K high stage with a variable speed blower is Rheem/Ruud. Would like to see more of them, especially for southern climates. The higher capacity variable speed blowers are great for cooling, but the minimum size heat is large enough for winter. For sizing I think the installer did the best he could within the choices of his lineup. In moderate heating climates I question even installing a gas furnace for the upstairs. Depending on your layout and energy costs a heat pump may have been a better choice. Lower BTU, cooler delivered air. Longer cycles, better comfort.
However what you have is what you have, you will have to decide how long you want your cycles to be (comfort vs. efficiency) and have the thermostat programmed accordingly.
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I'm pretty sure that our AC was size properly, but sometimes it short cycles as well. Sometimes the air coming out of the vents is not very cold unlike our main level system which blows out ice cubes.
The tech who serviced our furnaces said that he does not like Rheem/Ruud that much, but of course that's his own opinion.
I do wish that we did ask for a quote for a heat pump, because that is what we have for our basement system and our main level system (main level system is dual fuel). We always have our thermostats running on a program.
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