Duct and Vent sizing for 125,000 BTU Heil 92%er

[Gyva]

Hello everyone, I have a qusetion for ya and this is after hours of searching for the info myself online with no luck. I have a brand new Heil ultra high effecient DC90 furnace ,that I snagged for $100 still crated its rated at 125,000 btus which is going to be a little bigger than I need but for the $100 I am going to use it as I am in a very rural town a 100 miles away from any HVAC store... sooo, I need to know how many sq. inches of return air grill to install and how many sq inches or vents to install and sizing of the ducts. I want to get this correct as undersizing will cause stress on the blower motor and heat exchanger and cause them to be short lived. if I had to guess I would say my house is just shy of 1000 sq feet with 9 foot celings, I know I know kinda small for the btu but I believe I can make it work with the right duct system and the unit will probably only run for short intravals at a time. I have 2 bedrooms, one bath, one living room, one kitchen, and one dining room I planned on a tottal of 7 vents so I might need them to be larger to let the unit breath.... if you can help or point me in the right direction that would be great thanks.

blower motor specs are 3/4 horse 1075RPMS
Also house has no exsiting duct system so all will be from scratch.

Mike.

[totaleclipse]

Sorry, but this is not a DIY site. The best advice I can give you is to not attempt to install your discount unit yourself, and unless you have a load cal saying you need that much heat, I wouldnt let anyone else install it.

[amd]

A 125k furnace will shortcycle like crazy in your house, unless you don't have any insulation. (Not to mention most likely overheat and trip the high limit switch on the existing duct system)

Don't be cheap - contact an HVAC contractor and get it done right.

[Gunnery Sergeant Hartman]

Hope you can find a deal like that on cemetary plots and funeral arrangements for your family when you kill them.

[m kilgore]

Wow. I can't even believe you would think of using a furnace of that size for a 1000 sq ft house. Don't do it and be cheap with your families safety. Get a properly sized furnace installed by a pro.

[t527ed]

how close is your neighbors house?



if its the same size as yours you could probably run some ducts over for him.

[beenthere]

Hey. Whats wrong with using a furnace that 4 to 5 times the size you need.

Apparently. Giving you this info would be useless. As you have a problem reading and following instructions.

Since you asked for DIY instructions, on a NO DIY site.


Is this a troll.

[Gyva]

thats weird, I worked on an airforce base for 2 years as a HVAC tech, Mountain Home Idaho to be exact and although I never installed a system from scratch I did install many many units out there over them 2 years and I saw their homes were 1500 sq feet and they had the same 125,000 BTU rating. I figured I could make it work in a 1000sq foot home with proper breathing ducts....

I know it can work safely with the right duct runs, I'll continue my search elsewhere...

[beenthere]

They ran. They most likely did not work right.

For your 125,000 90% to maintain a 55° temp rise. You wqill need to move 1890 CFM.
Thats enough air that it will exchange all the air in teh house in lees then 5 minutes.
As an average, your 7 vents will have to move 270 CFM each.

If you don't move enough air, it will short cycle, and use a lot more gas.


PS: Did you derate those furnaces. Mountain Home Idaho has an elevation of 3146 foot.