Shouldnt a dual stage furnace save you money on natural gas?
So first cold snap with my new furnace installed Apr 2021. Went from a 100K single stage 96% efficiency to an 80K dual stage 97% efficiency. Tons of research and quotes done, spent a lot of time to make sure I was doing what I assumed was right. Contracter that installed did a lot of preliminary checks and work with me as well.
To add, I also have a dual zoned system in a bi-level, Total sq. footage with both floors is 2645 according to the real estate sheet
Highest Natural gas usage since Ive lived in the house for 3 years. Even compared to Feb 2021 cold snap that lasted longer and was colder. Used 6 GJ more in natural gas than my old single stage furnace when it was extremely cold Feb 2021
And yes I know a lot of factors contribute to NG usage. but the lifestyle of the house hasnt changed. Using the same settings on the ecobees, run times, etc Sure I adjust things with the 2 Ecobees, but I adjust to help with comfort and savings. IN one day I have 6 different comfort settings.
I thought these things were supposed to save a person money using single stage to keep the temps level in the house, or to only use single stage for those slight adjustments in heat as needed.
I called the installer to see if it maybe over firing or something as well, and he is coming to check.
I understand fluctuations, but to me I should be using less gas when its cold, not more. And if it was close to the same usage, sure. But this is alot of usage. In the cold weather, yes I assume dual stage will be used way more. But even so, it is a smaller furnace to.
Went from a 100K to an 80K furnace as well. And while the furnace kept up, it wasnt running 24/7 to keep to the cold either like an undersized furnace would. But as well, it wasnt short cycling or anything like that. Temperture rise in the morning of a 4 degree setback was around 2 hours, sometimes 2.5 when it was really cold, -35.
AS well, with my zone panel, I can adjust how long my single stage stays on. I know many on here say single stage runs for 15 minutes, than of course goes to dual stage when it cant reach the temp you want. I have mine set for 30 minutes. Its adjustable from 7 minutes to 47 minutes.
Curious on the use of dual stage and the length of time single stages can run. Always read different opinions on different sites. And of course comparing dual stage to single stage. Some sites saying dual stage really doesnt save you as much money as having single stage in extreme winter temperatures. Many on this site have said how they have their single stage run "all day" How can it run all day on single stage if after 15 minutes and the set temp isnt reach, dual stage runs. Or does that mean that only single stage is used during the day when it calls for heat, not that their single stage runs ALL DAY. To me all day would be your furnace runs on the first stage for, well 8 hours straight,
Single stage - 100% all the time
Dual stage - 70%, then 100% when needed
Since dual stages can be controlled by the furnace board or the Thermostat as well.
Does less gas get used to have single stage run a shorter time (say 10 min) before going into dual stage, which would make the total run time shorter. Or have the single stage run longer before going into second stage, which would make the total run time longer
Basically, for NG use, is it better
- Use 70% for a longer time, and 100% for less time, but taking a longer time to reach the set temp. (1 hr as an example)
- Use 70% for a shorter time, and 100% for more time, but taking a shorter time to reach the set temp. (45 minutes as an example)
I realize for a regular mild winter day, that dual stage probably comes out on top since it would just use the first stage only to keep your house temp level.
But what about -30 and beyond, usually a house takes longer than 10 minutes to reach your set temp, so then it will use dual stage anyway, making the run time longer. Is that when single stage is better, starts off full blast and warms up the home faster, and then shuts off sooner? The house will loose the same amount of heat after the heat isnt on. So the next time it cycles, single stage or dual stage, that wont change.
This is for correctly sized furnaces. Comparing the same size furnaces, 80K vs 80K (as an example)
Are there online calculators that can be used, or some simple math Im just not seeing right now.
As well, so many sites say this. "By using a longer, low output, heat cycle in Low Output mode, 2-Stage Furnaces are able to minimize coarse temperature swings within your home."
But most systems only stay on the first stage 10-15 minutes, and if more heat is needed go to 2nd stage. How can you make your 1st stage run longer all day. Some sites say your furnace should be running 80% of the day in 1st stage. But how can the first stage run all day to maintain the heat. Doesn't that temperature get reached eventually. And if not, then wont the furnace just go to 2nd stage since it cant reach that set temp?
So after all that, am I costing myself more money on Natural Gas having the 1st stage run longer than 15 minutes, instead of having the second stage kick in sooner?
As well, my Ecobees cant control the staging, because my zone panel is the brains in between my 2 Ecobees and the furnace. So I cant do things like reverse staging, or have it kick into 2nd stage right away when it knows the temperature increase it needs will be longer than 15 minutes.