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View Full Version : What size feed to most forced hot air furnaces?

Ne_EC
06-16-2007, 07:31 AM
Have been working a project, and I can't get in touch with the contractor who's installing the forced hot air furnace. What is typical feed to a furnace that would be in a 2,000 sq ft house?

Also, the owner is considering A/C. What size unit, and what size feed would a house this size get. Just want to anticipate what size wire I'm going to be running. On A/C what have you guys been typically putting in for a disconnect?
iwire
06-16-2007, 07:46 AM
What is the furnaces source of heat?

Oil, Gas or Electric?

Oil or Gas 15 amps should do it, 20 at most.

If it's electric all bets are off.
Ne_EC
06-16-2007, 07:47 AM
Sorry - it's gas.
peter d
06-16-2007, 08:51 AM
Rule of thumb that I go by is all boilers (hydronic) get a 15 amp circuit, oil or gas.

Small furnaces get a 15 amp circuit and large furnaces get a 20.
Dennis Alwon
06-16-2007, 08:54 AM
Have been working a project, and I can't get in touch with the contractor who's installing the forced hot air furnace. What is typical feed to a furnace that would be in a 2,000 sq ft house?

Also, the owner is considering A/C. What size unit, and what size feed would a house this size get. Just want to anticipate what size wire I'm going to be running. On A/C what have you guys been typically putting in for a disconnect?

Bob has answered the gas deal-- 15 or 20 amp circuit. Be safe and pull a 20 amp circuit.

The a/c varies and you need to contact the hvac dude and get the specs on the unit. I suspect a #10 will work but it will depend on the efficiency of the unit that is installed.

I use a diso that has a GFCI mounted in the enclosure. It is a fuseless disco pull out with a GFCI receptacle mounted in the enclosure. You would probably need to bring a 120v circuit (not a separate cir. unless you want to) with the a/c circuit.

The disco on the left has the GFCI in it.

http://news.thomasnet.com/images/large/463/463936.jpg
Brady Electric
06-16-2007, 09:15 AM
I agree with all the answers. Dennis where do you buy those disconnects? I have never seen them. Semper Fi. Buddy
stickboy1375
06-16-2007, 09:29 AM
Which disconnect? The GFI installed or the standard 60amp non-fusible disconnect?
stickboy1375
06-16-2007, 09:34 AM
From past experience, I wouldn't worry about the size of the outdoor unit until the unit is installed at the job site...
bjp_ne_elec
06-16-2007, 09:43 AM
Dennis - what is the GFI for? As far as I know, it's not required for a A/C. Do you maybe use this for a Hot Tub?

Dave
Dennis Alwon
06-16-2007, 09:54 AM
Dennis - what is the GFI for? As far as I know, it's not required for a A/C. Do you maybe use this for a Hot Tub?

Dave

Dave look at article 210.63 .

Dennis where do you buy those disconnects? I have never seen them. Semper Fi. Buddy
Today 07:54 AM

Check with your supply company. They need to start stocking them if they don't already have them.
mdshunk
06-16-2007, 11:06 AM
For gas furnaces, I've generally been running a 20. Reason being, most gas furnaces nowadays are condensing furnaces, so that gives me a little bit of capacity for the necessary condensate pump, and possible ozone generator and humidifier to plug into also. Some of these furnaces are marked 15 amp max, so you sometimes have to use an SSU cover at the furnace if you ran a 20.
iwire
06-16-2007, 11:10 AM
so you sometimes have to use an SSU cover at the furnace if you ran a 20.

Is that really legal?
mdshunk
06-16-2007, 11:13 AM
Is that really legal?How do you mean? No different than if I ran a 100 amp the the furnace, then put a subpanel next the the furnace and popped in a 15 amp breaker to serve the furnace. Is it? Maybe SSU was the wrong part number (it was off the top of my head), but the idea is the same. I've seen 50 amp parking lot lighting circuits, with fuses in each pole base to protect each fixture on the "ring".
iwire
06-17-2007, 08:16 AM
How do you mean?

I wish I knew.

I think I recall reading somewhere that those cover mounted fuse holder where not rated for branch circuit protection.

That said, I can not find anything that backs that up so there is a good chance I am mistaken.
Dennis Alwon
06-17-2007, 08:46 AM
So what the heck is an SSU?
iwire
06-17-2007, 09:02 AM
So what the heck is an SSU?

A handy box cover with an Edison base fuse holder and switch

http://img.products.howstuffworks.com/cctool/PrdImg/images/pr/177X150/00/01/ff/dd/b4/33545652.JPG
Dennis Alwon
06-17-2007, 10:14 AM
A handy box cover with an Edison base fuse holder and switch


Thanks Bob-- but why install that. All you need do is put a 15 amp CB in the panel.
iwire
06-17-2007, 10:18 AM
but why install that. All you need do is put a 15 amp CB in the panel.

Read Marc's post 11. :)
mdshunk
06-17-2007, 10:23 AM
Thanks Bob-- but why install that. All you need do is put a 15 amp CB in the panel.SSU's (and similar plates) were realy popular in the 60's and 70's when many warm air furnaces and boilers specifically called for 6-1/4, 8, or 14 amp fuses.
augie47
06-17-2007, 10:24 AM
I think I recall reading somewhere that those cover mounted fuse holder where not rated for branch circuit protection.

That said, I can not find anything that backs that up so there is a good chance I am mistaken.


In reading 240.50, I would think they would have to be have to be type S fuseholders.