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enemydream 03-17-2011 03:41 AM

Furnace keeps shutting off
 
We recently replaced the furnace in my house last November with a Rheem 92 effienct and it was shutting off every 10min it seemed like. The people installed it put a 2nd vent into the basement to try and help the airflow cause they said it was getting to hot and shutting itself off. I'm relatively new to the scene but is there anything I can do to help the situation so that next winter my house wont be as cold even with the furnce running (or rather shutting off every 10min) non-stop. Bigger vent piping, vent boots? Thanks.

beenthere 03-17-2011 04:38 AM

Post full model number of the furnace. Along with the sizes of your supply and return trunk lines, and branch supply lines. From there, we may be able to give you some ideas of what you need to do.

Sounds like they took out an X input size old 80% furnace, and put in the same input size 92% furnace. Without giving consideration that the new furnace needs to move alot more air then the old one did.

EG: An old 100,000 BTU input 80% furnace may have only needed 820 CFM of air flow. A new 100,000 BTU input 92% will need around 1220 CFM.

The old heat exchangers were made of heavier metal, and could take higher temps, then the new thinner heat exchangers can.

Marty S. 03-17-2011 05:05 PM

Tell the company you want the duct static pressure tested. Inside the furnace there's a sticker listing all kinds of information, one of the lines will say max. external static ---. Your duct must be big enough to keep the reading below that. Adjusting duct to make the furnace work properly should have been included in the bid so before you go all DIY get the installing company to correct the issue.

1mastertech 03-18-2011 03:52 AM

it definitly sounds like an airflow problem with the furnace.you can take a temperature reading between the air going in and the air coming out to tell you how much of a temperature rise you have going on. all the posts are good ones.The blower speed could be increased a little. You want to make sure the return air duct is large enough to pull air across the heat exchanger.This might seem odd but make sure all the registers are open to distribute the air

enemydream 03-19-2011 02:46 AM

Rheem Classic 90 Plus with Dual Comfort control - RGRK , Input Rates from 105,000 to 120,000 BTU/HR
http://rheem.com/product.aspx?id=D56...8-1417B695E4CE

Their initial solution to correct the issue was to add a bunch of vents into my basement, which is completely unfinished and completely unused by me and my family. I just wanted to get them out before they cut a whole bunch of holes in my vent pipes. They got up to two before i found out.
It intakes to a wide area that is between the joists near the furnace into a 18x14 chute. It exits to 18x8 ductwork that transitions a few feet away into 14x8 ductwork that has 6" diameter piping leading to the vents. The old one was comparable to %80 with one stage. We got this one with hopes of installing a heat pump in the future.
The second floor of my home recieves about nil of this and we had to resort to heated blankets for real warmth. The upper vent travels straight up the chimney (right next to the furnace) to 3 wall vents, the furthest of which receives the most heat (perhaps because it feels this way cause it's the smallest room? Idunno) Is this something the installers should have corrected for me and or will they now besides making my basement a warm place for the bugs to live. :laughing: It wasn't in the original estimate however, just install and they did that but yeah. Thanks for the help people.

beenthere 03-19-2011 03:47 AM

18X8 duct is a bit small for a 70,000 BTU 95% furnace. So its no where close to big enough for yours.

Tell them you want the right size furnace. Does your state have a state licensing board. If so, you may want to call them.

enemydream 03-19-2011 11:51 AM

My house is 1750 sq. ft. with 1000 of it being on the first floor. They calculated and picked the furnace based on that or so they said.

beenthere 03-19-2011 04:29 PM

Quote:

Originally Posted by enemydream (Post 612589)
My house is 1750 sq. ft. with 1000 of it being on the first floor. They calculated and picked the furnace based on that or so they said.

Mines 1650 sq ft, story and a half. Only needed 50,000 BTUs to keep the house warm when we were at -6F.

Hard to believe that extra 100 sq ft you have, needs that much more heat.


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