Reply With QuoteThe two are not related in fact, high efficiency furnaces typically have a lesser temp rise. The differences you are feeling is ducting distribution and fan speeds.
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95% efficiency unit vs 80% efficiency unit
Hi folks,
Just a general question for you. Is it true, that the 95% efficiency furnace will produce warmer heat coming out of the registery than a unit that only does 80% efficiency?
In my previous home, I had a 95% efficiency unit installed and the air coming out of the registery was very hot. Since we moved, this unit is only 80% efficiency, is air coming out is only luke warm....
please let me know
thanks
The two are not related in fact, high efficiency furnaces typically have a lesser temp rise. The differences you are feeling is ducting distribution and fan speeds.
If Payback is so important to you, why are you not driving a Toyota Corolla?
If you also have central air conditioning, the fan speed may be set to promote that which typically wants a higher flow rate than heating. It doesn't always change based on the mode, you have to do that yourself. Many times, you can adjust the fan speed to be slower which allows the air to absorb more heat as it goes through the heat exchanger. You must keep it above the minimum for the system's heat output or you risk overheating the exchanger. The manual should show you your valid options.
Jim DeBruycker
Important note - I'm not a pro
Retired Defense Industry Engineer
If the ducts and fan speed were the same you would get air theoretically 15% warmer. You are putting 15% of your heat in the garbage can in this house.
If our GOV banned 80% rigs, the cost of the 95% units would drop dramatically.
The efficiency of the unit has NOTHING to do with how hot the exiting air is...it is all dependent on the heat exchanger design, the fan speed, and the distance and state of the ductwork before it hits the register. If the ducts run through unheated space and are uninsulated, that may be the primary reason the exit temp is cooler. Have you actually measured the temperature at the register? Just like a cooling breeze in the summer feels cool, it will feel cool in the winter, too if you can't slow it down a bit.
Jim DeBruycker
Important note - I'm not a pro
Retired Defense Industry Engineer
Ball valve
Actually if you compare similar size furnace from same manufacturer you will quickly notice higher recommended temp rise on 80%ers in order to maintain higher flue temps to avoid condensation of ht exh and flue. Thus 90%ers which there is a desire to condense have lower temp rise allowances meaning more cfm's across ht exh, resulting in cooler discharge temps.
If Payback is so important to you, why are you not driving a Toyota Corolla?
yes, the 80% out puts temp at the register at 131, returns 72 when themostat is set at 74 (winter). The temp rise is 59, as this is when fan speed is set at med-low.
I think thats what I said. In reverse. Anyway, its nuts to toss 15% to 20% of our precious natural gas. This is ONE place we need some regulations to make the MFG's go all condensing.Originally Posted by jadnashua
Yep, which is why I bought another 80 the last time round.
High efficiencies are still too expensive to make the investment worthwhile. At least for people that don't intend to die in the houses they currently live in.
It's hard to fix a Trane.
Which is why I went for a Bryant 80 variable speed instead (I'm willing to pay for peace and quiet).
I'm surprised you need heating in California.
Gets a bit chilly at home in California from time to time.
I installed a Rheem 93% efficiency condensing gas furnace a few years ago. It replaced a unit that was about 20 years old and no more than an 80% efficiency rated model. The newer unit is 2 stage......has a low fire and a high fire burner and also the fan speeds change with the burner output. NO doubt whatsoever it saves money and is warmer.......I saw about a 20% lower gas bill the first year I had it......and it IS warmer at the heat registers.
The efficiency rating has nothing to do with the heat temperature though. I did the heat rise measurments instructed in the install manual. It was perfect and I did not need to change the fan speeds to adjust that temp. rise. The high efficiency is simply from not letting wasted heat go up the chimney.......I have luke warm air going out a side wall thru pvc now instead of hot gas going up a chimney. Most of the heat energy gets into the house instead of going out the chimney....
I love the unit and am going to install a second one in another unit I have that still has an older low efficiency furnace.....
Is that a tree house Ballvalve?
I see. perhaps the town home that I sold (95% efficiency) unit had warmer air coming out at the registry had to do with more heat energy gets into the house like the way yours work. Our current home ( A SINGLE HOUSE) gets luke warm air coming into our registry figured it's due to 80% efficiency unit.
curious, what was your temp rise when you did the measurement? Mine was at 59 degrees which is right smack in the middle of the unit manual 40~70.
I think my temp rise was right in that area.....60 degrees. ?? It's been a while....
My house is old.....has sheet metal ductwork that is not insulated. I turn the heat down during the day and at night to save $$$. It fairly quickly warms up once I turn the heat up.....but hot air heat in an older poorly insulated home is not great. I added a humidifier when I installed the furnace and between the 2 items it is better but I sure wish I had a fireplace or pellet or wood stove.......
IAN: Is that a tree house Ballvalve?
Not a tree house, but bolted to bedrock just above two waterfalls.
I'll try and post another opposite view.
Last edited by ballvalve; 01-17-2011 at 01:11 AM.
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