Furnace in attic doubling as AC air handler ?

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ritelec

Senior Member
Location
Jersey
Will make a call to rheem.

But. Are they now making combo heat ( furnace ) / cooling (air handlers ) ?

I don't doubt it now adays. But the unit says (at least what looks like the heating side and really don't see a side for AC. but I'm told it's AC too and there are refrigerant linens going into it ) 8.9 amps at 115v. Max ocp 15.

The 115v has me doubting it. Do they now make 115v AC air handlier units. Thought air handlers where 240v ???

Thank you.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
Will make a call to rheem.

But. Are they now making combo heat ( furnace ) / cooling (air handlers ) ?

I don't doubt it now adays. But the unit says (at least what looks like the heating side and really don't see a side for AC. but I'm told it's AC too and there are refrigerant linens going into it ) 8.9 amps at 115v. Max ocp 15.

The 115v has me doubting it. Do they now make 115v AC air handlier units. Thought air handlers where 240v ???

Thank you.

When you say air handling unit (AHU) do you mean just the blower section or are you including the condenser unit? My HVAC has the furnace and blower in the basement and runs on 120VAC. The condenser is a separate unit that sits outside and has a separate double pole 40amp breaker for its power.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Will make a call to rheem.

But. Are they now making combo heat ( furnace ) / cooling (air handlers ) ?

I don't doubt it now adays. But the unit says (at least what looks like the heating side and really don't see a side for AC. but I'm told it's AC too and there are refrigerant linens going into it ) 8.9 amps at 115v. Max ocp 15.

The 115v has me doubting it. Do they now make 115v AC air handlier units. Thought air handlers where 240v ???

Thank you.


The air handling has a coil in the ducted area and has been doubling for the heat as long as I can remember. Why would you have 2 sets of ducts and blowers when it can be done with one. You are used to radiator or hot water furnaces and not central units-- my guess. Once a central system is installed it usually does both cooling and heat-- cost effective even though a hot water system may be more comfortable
 

electricmanscott

Senior Member
Location
Boston, MA
Sounds like a hydro/air system. Boiler to heat the water that flows through the AHU coil providing hot air and AC condensor for the refrigerant. Usually 120v. Definitely not a "furnace" at 15 amp max ocp
 

kwired

Electron manager
Location
NE Nebraska
Air handlers designed to accept electric heating strips are generally 208-240 volts, and typically are powered from one of the heater circuits, if they are for other heat sources they are often only 120 volts, unless over 1 HP blower anyway.
 

growler

Senior Member
Location
Atlanta,GA
Will make a call to rheem.

But. Are they now making combo heat ( furnace ) / cooling (air handlers ) ?

I don't doubt it now adays. But the unit says (at least what looks like the heating side and really don't see a side for AC. but I'm told it's AC too and there are refrigerant linens going into it ) 8.9 amps at 115v. Max ocp 15.

The 115v has me doubting it. Do they now make 115v AC air handlier units. Thought air handlers where 240v ???

Thank you.

Who is installing this thing? It should be installed by a licensed HVAC contractor that knows what they are doing.

They set the air handler in place and you run your circuit to a disconnect switch and then to the unit ( 120V ). You provide a receptacle for the condensation pump and a light for service and that's pretty much it for the electrician.

The AC condensor will be 240V but the HVAC guys will set that also and you will look on the name plate for circuit and breaker/fuse size. You run power to the disconnect and then either you or the HVAC contractor can hook up the unit. They may need a service receptacle for the condensor unit if one doesn't exist.

Getting the lines form the condensor to the unit and any plumbing for gas or whatever is the HVAC contractors problem
 

growler

Senior Member
Location
Atlanta,GA
Sounds like a hydro/air system. Boiler to heat the water that flows through the AHU coil providing hot air and AC condensor for the refrigerant. Usually 120v. Definitely not a "furnace" at 15 amp max ocp

He didn't say it was an electric furnace. It can be a gas furnace or propane and still only need 120V and 15 Amp circuit for the blower and controls.
 

electricman2

Senior Member
Location
North Carolina
Occupation
Retired Electrical Contractor
Sounds like a pretty standard set up to me. A furnace, either gas or oil (gas probably since in attic) with a cooling coil in supply plenum. 120 volt supply. Condensing unit located outside with its own 240 volt supply. Pretty common around here.
 

Dennis Alwon

Moderator
Staff member
Location
Chapel Hill, NC
Occupation
Retired Electrical Contractor
Sounds like a pretty standard set up to me. A furnace, either gas or oil (gas probably since in attic) with a cooling coil in supply plenum. 120 volt supply. Condensing unit located outside with its own 240 volt supply. Pretty common around here.


Pretty common everywhere
 

ritelec

Senior Member
Location
Jersey
Thanks all.



Furnace

I talked to the AC guy today.

Two condensers outside one for second floor. One for first.

One of these furnace airhandler things in attic for second floor. One in basement for first floor

120v
 

norcal

Senior Member
Sounds like a pretty standard set up to me. A furnace, either gas or oil (gas probably since in attic) with a cooling coil in supply plenum. 120 volt supply. Condensing unit located outside with its own 240 volt supply. Pretty common around here.

Sounds like every cheap tract home around here.:lol:
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
Air handlers use to be primarily 240 volts but I'm seeing more of them 120 volt.
From my experience when an AHU in a residential setting is solely for AC then it customarily runs on 240 VAC for efficiency. When it's coupled up with a furnace it runs on 120 VAC. Pretty typical as most have mentioned.
 

iwire

Moderator
Staff member
Location
Massachusetts
From my experience when an AHU in a residential setting is solely for AC then it customarily runs on 240 VAC for efficiency. When it's coupled up with a furnace it runs on 120 VAC. Pretty typical as most have mentioned.

There is no kWh savings by using a 240 volt motor.

The same design 1 hp motor running at 120 or 240 will cost the same amount of money to run. We are charged for watts not amps.
 

goldstar

Senior Member
Location
New Jersey
Occupation
Electrical Contractor
There is no kWh savings by using a 240 volt motor.

The same design 1 hp motor running at 120 or 240 will cost the same amount of money to run. We are charged for watts not amps.
That's interesting. What would be the thought behind the design decision to make a combo unit run on 120 rather than 240 ? Why not make them all run on 120 ? It only takes up one breaker space not two.
 

kwired

Electron manager
Location
NE Nebraska
That's interesting. What would be the thought behind the design decision to make a combo unit run on 120 rather than 240 ? Why not make them all run on 120 ? It only takes up one breaker space not two.
Air handlers designed to accept electric heating elements typically are set up for 208-240 probably mostly because that is what the heat strips will require, and the blower and controls typically get tied to one of the heat strip circuits when heat is installed.

More recently - AFCI protection requirements will apply to a 120 volt circuit if it is a 15 or 20 amp circuit and in a space where AFCI is required, but same unit on a 240 volt circuit of any ampere rating would not be.
 

iwire

Moderator
Staff member
Location
Massachusetts
That's interesting. What would be the thought behind the design decision to make a combo unit run on 120 rather than 240 ? Why not make them all run on 120 ? It only takes up one breaker space not two.

I won't begin to guess why certain makers do things a certain way.

However in general the only cost reduction with running motors on higher voltage is reduced size wire and control equipment.

However that savings may not be worth it if it means more expensive breakers or needing more panel space due to multipole breakers.
 

gadfly56

Senior Member
Location
New Jersey
Occupation
Professional Engineer, Fire & Life Safety
I won't begin to guess why certain makers do things a certain way.

However in general the only cost reduction with running motors on higher voltage is reduced size wire and control equipment.

However that savings may not be worth it if it means more expensive breakers or needing more panel space due to multipole breakers.

I'm guessing that the missing piece of the puzzle is that some folks are talking about heat pumps and others about furnaces. I suppose if you're already running 240 to the heat pump for the auxiliary heat strip then popping in a 240 fan makes sense since you are, as you point out, saving a little bit in material. Over thousands of units it will make a difference for the manufacturer.

On the other hand, your standard furnace may or may not have AC associated with it. In that case, as you point out again, there's no advantage to the 240 volt fan and in fact you might not have enough poles to put the furnace in, especially if it's a retrofit. In that case, 120 volt fans make all the sense in the world.
 

mtfallsmikey

Senior Member
In recent years, in order to cut manufacturing costs and the number of different models of air handlers/furnaces, etc. they have come up with "multi-poise" or equipment that can be configured for upflow, counterflow, and either left/right horizontal configurations. I have installed A/C units, condensing gas furnaces, as well as heat pumps with A/C., hydrocoils, and resistance heat. Most all straight air handlers can be configured with all kinds of accessories.
 

Jraef

Moderator, OTD
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Air handlers use to be primarily 240 volts but I'm seeing more of them 120 volt.
One reason is that a lot of the newer energy efficient units are using ECMs, Electronically Commutated Motors, that are essentially like having a VFD and motor in one unit. So what voltage you give it is less relevant now because all it does is internally rectify it to DC first anyway.
 
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