# I need help wiring in my new electric forced air furnace...



## daveomak (May 27, 2020)

I have a furnace in the attic..  I'm installing this furnace inside my home to eliminate heat loss due to duct work etc..  
When my attic is 10 F,  the 150+ ft. of duct work doesn't cut it...  OH !!  FWIW, my home is 75 years old..

What I want it to do...
I need heat..... 
I need "summer fan" switch so I can have the fan run continuously....
and I need to hook up the thermostat.....
and I want to know how to adjust the fan speed...

I'm an IDIOT when it comes to electrical diagrams... 
The furnace is a Goodman HKR-10.....  Rev C....  Air Handler    9.5 KW / 240v...  34,120 BTU 10KW

I think this unit does not have a variable speed fan....   Can you tell me how I can make it variable speed ??

I plan on a simple bi-metal thermostat...  maybe...   What do you think ..

OK..  What have I forgot....









	

		
			
		

		
	
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## DIYerDave (May 27, 2020)

Looks like you have a 2-speed motor. (Hi/low). You will probably need to install a relay to switch the speeds.


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## bill1 (May 27, 2020)

"Furnace" made me think of gas burners, but this appears to be all-electric heat source based on HKR-10 product literature.  This will be costly heat...if it's running 20% of the time 6 months of the year, that's an average power draw of 10% of 10kW or 8760 kW-hr per year, not counting the blower motor (probably an MBR-0800?) power.  At about 20 cents per kWh, that's  almost $2000 every year just to pay for the electricity for this.  

 This is a lot of electricity....probably a 60A circuit at normal household split-phase 240V.  If you don't already have this installed, you'll probably need a pretty costly upgrade to your electrical feed and main panel.   

Per unit of heating energy, gas is about half the price of electricity (especially since fracking became so financially attractive) so upgrading your existing furnace to give you an extra 34000 BTU/hr would soon pay for itself in just a few years.  You may want to spend a little money wrapping better insulation around the existing ductwork in your attic and you may find your existing furnace (without this 10kW electrical heater) gets you plenty warm and with no added energy costs.  

If the blower really is an MBR-0800 it's probably already wired to run at max speed to keep the 10kW filaments from overheating and burning the house down so a single jumper would allow you to run the blower non-stop in the summer (with a $20 thermostat set to min so filaments never fire up) but do you maybe want to re-think the cost/benefit analysis on this first?


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## daveomak (May 27, 2020)

Bill, I have run the cost benefit analysis...
I use 6 tons of pellets per winter and $200/ton = $1200/7 months per winter or ~$171per month for heat only....
1 ton of pellets @8,000 BTU per pound X 2,000# X 6 tons = 95M BTU in heat... = ~28,000 kW hours
28,000 kW hours X  $0.07 =  $1,960 for heat....
My pellet stove works "overtime" as is runs continuous so it's wasting probably 20% of it's heat and it's probably 85% efficient so there's another 15% wasted....
So, theoretically, let's "assume" it's total efficiency at 65%...  
95M BTU X 0.65 = 62M BTU to actually heat the home at a comfortable temp...
So that $1,960 electric bill now becomes $1274 for the 7 month period...
PLUS....  it gives me the opportunity to leave my home and not have it freeze...   
Currently I only have a pellet stove for heat...  When the temperature doesn't get above freezing for ~4 months, that's a problem....
In post 1 I noted I was replacing a furnace in the attic...   It is also electric and it's HUGE...  And it wastes a lot of heat being in the attic... So, I have the electrical already in place... 
My pellet stove is rated at 30,000 BTU's...  The NEW electric furnace is 35,000 BTU's...  Since electricity is 100% efficient the costs are about equal...   I'm gonna use the electric as a "base" heat and supplement it with the pellet heat...  I'm thinking set the thermostat at ~65ish and burn a few pellets to raise the temp up a bit...
There is another plus to this...  having an AIR FILTER to knock down the dust...  I have 4" thick pleated filters with carbon secondary to clean the air...  they are waiting for the install....
I just wish I could understand the electrical schematic.....


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## daveomak (May 27, 2020)

DIYerDave said:


> Looks like you have a 2-speed motor. (Hi/low). You will probably need to install a relay to switch the speeds.



Where and how do I do that ???
--------------
_I need heat.....  _
Which wires do I connect the incoming 220V to ??

_I need "summer fan" switch so I can have the fan run continuously...._
Which wires do I connect to to have a summer fan ??

_and I need to hook up the thermostat....._
Which wires are the thermostat ??

_and I want to know how to adjust the fan speed..._
How do I hook up the relay, and what relay should I get ??


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## DIYerDave (May 27, 2020)

I suggest you go visit your local HVAC tech guy and give him all the specs of the furnace. He should be able to help you figure it out. Plus he will have the type of thermostat and relays you need.


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## bill1 (May 28, 2020)

7 cents per kw-hr...do you live in Finland?  I want the Tesla dealership in your town!  

The pictures aren't consistent with the schematics you show.  There's a lot of variation in products like this.  E.g. this $73 HKR-10 has a different filament layout than this $73 HKR-10. Note the Amazon is closest to what you have (just a single mounting plate) but it clearly has a connection for the beefy 50A fused 240V input connections. Yours doesn't have that...your photos don't anywhere show wiring consistent with 10kW so it's hard to tell you where to connect power. I see holes (above the white strip with all the black arrows) but the big terminal block is missing. Is that lying around somewhere?

The schematic we really need is on the right side of your picture *DSCF0052.JPG *but it doesn't agree with what you attached. The page 8 wiring diagram would imply your blower is the 10kW model MBR0800. But note that has 4 wires leading to the motor--red,green,white,blue. But from your picture (left side of *DSCF0050.JPG*) you have 5 wires (note the brown wire) which is for _over _10kW models. That alone isn't a big deal but the 5-wire motors have a capacitor start circuit EXTERNAL to the motor. I note your dscf0049-jpg picture appears to show a capacitor going off the picture. It's critical that's connected between the blue and brown wires or you'll burn up your motor. But again I don't trust your posted wiring diagrams so take even that with a grain of salt.

Perhaps the other Dave can explain, but I see nothing to indicate you have anything other than a single speed motor.  This thermostat probably will work (note the green wire allows you to run the fan independent of the heat) but we'll need the real schematic to know how to hook it up.


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## daveomak (May 28, 2020)

OK...  Here's more information...  Sorry I missed this stuff earlier...

Schematic inside the furnace..






Fan and capacitor...






Wiring going inside to the controls...






Where the wiring comes through the bulkhead....






What I think is "POWER IN" terminal block...






Ground lug....






Heating element terminals....






Element sticker...  9.5KW and part #..






Heating element...











OK...  I think I may be getting close to figuring this stuff out....

I'm thinking I need a 50 or 60 AMP FEED THRU circuit breaker at the furnace...  I have a 60 amp in the panel....  *Is that correct ???  which one ???*
Connect the "colored" (black) wires to those "Power In" incoming terminals...
Connect the ground wire to the ground lug...
Do not connect the common wire anywhere...  Dead end it....   *Is that correct ??*

Lets forget all the incorrect stuff I put up...
So, which wires to get the thermostat to work ???
Which wires to run the "summer fan" using a single pole/single throw toggle switch or light switch ??
What else do I need ???


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## daveomak (May 28, 2020)

YES !!!  7 cents per KW hour....  When I moved here it was 3.5 cents per KW hour...


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## daveomak (May 28, 2020)

Don't give up on me now, please....


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## JC in GB (May 28, 2020)

According to the schematic, you have an option for a three speed motor.  Is that the model you have?

If I knew a bit more about the blower motor specs, I could suggest a motor speed controller.

JC


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## daveomak (May 28, 2020)

I don't think so...  But I was thinking I could add a SCR motor speed control to it...    but not sure....


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## chopsaw (May 29, 2020)

Been a long time since I worked on them .
Blowers motors normally have 2 speeds , one for cooling one for heating . Cold air doesn't rise , so needs a higher fan speed .

Your drawing shows wiring changes for 3 speeds ( on some units ) length of run , temp of air to be moved needs different speeds . 

On the right side of the drawing , the heavy dashed lines are  line voltage in , that are  provided in the field . 

You have low voltage , 24 volts that controls the make up of the contactor , thru the thermostat . 
So 24 volts from the unit up to the therm , then back down to , heat , fan , or cooling if you have it . 
That's the section that says " see notes 2 and 6 " right side of the drawing . 
Says TR ( transformer ) read the notes in that area . 
Shows colors of the wire connections .


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## JC in GB (May 29, 2020)

daveomak said:


> I don't think so...  But I was thinking I could add a SCR motor speed control to it...    but not sure....



Not all motors can be controlled using an SCR controller.  With synchronous AC motors, speed is dependent on line frequency.  You must use a device known as a cyclotron to control that type of motor.  If you could get a pic of the motor nameplate I could likely figure out what speed control would work for you.

JC


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## daveomak (May 29, 2020)

Thank you, The motor is a witch to remove,,  I have to pull the fan and housing from the unit... 
The furnace model is... MBR0800aa-1 , hkr-10 Goodman 34,120 BTU ..  /The motor is inside the fan housing...
I'm thinking I will live with the blower speed...


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## zwiller (May 29, 2020)

The guys have you mostly but didn't see a response on breaker.  I am not licensed but knowledgeable and do elec work on the side.  No pass through needed, but should already have a disconnect at furnace, add one if not.  NEC 424.19.  http://www.codebookcity.com/codearticles/nec/necarticle424.htm

WRT fan, maybe an inline duct blower?


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## JC in GB (May 29, 2020)

If I lived near you Dave I would come by and give you a hand.....

JC


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## JC in GB (May 29, 2020)

I looked up the technical specs on your cooler unit.  The bad news is that your unit uses a split phase motor that is not easily subjected to speed control.

To do what you are asking, you would need to remove that motor and replace it with a 3 phase motor then run it using a variable frequency drive. 

It sounds like a major pain in the butt to do all that.  It would give you precise control though.

JC


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## bill1 (May 29, 2020)

Thanks for the added pictures, incl the motor start capacitor location.  I'd still appreciate seeing what the notes say (chopped off at bottom) on the _internal _schematic.  I doubt you have 3phase power at a residence so be happy this is all designed around split phase 240VAC.  
If you wire this to a 50A breaker, you'll need to wire at least 6AWG (#6) to this, use #4 if you're coming from a 60A breaker (or fuses).  I agree the terminal block you provided extra pics for is meant to be the input...but please verify a .20 drill (13/64 or #6) will fit in those terminals...I'm still concerned that this is somewhat of an orphan unit.  E.g. putting the ground stud kitty-corner from the attachment is "legal" but weird.  
Nice catch by zwiller on the NEC 424...you need a switch (disconnect means) in eyesight of this so I assume you'll need to get one...note it needs to be 2-pole for both of the split phase 240.  I note the Goodman product lit on line all shows that included...but apparently not for you.  
That terminal block is part of the main contactor that the thermostat will turn on and off (at 24V levels).  The two red and 2 black wires going to the filament connections look wimpy to me.  Verify they're at least #12.  Normally that's only good for 20A each (40A when paired) but for in-chassis wiring (lots of air cooling) that's OK.  
Note the contactor is not on the schematic I requested.  Are there any markings on it we can get some info?  There appears to be two relay connections...maybe one normally open and one normally closed?  We'll want the NO one.  For the CT31 thermostat I linked to, the W terminal will go there.  The terminal marked R will go to one of 3 unused spigots under the main power in terminals.  The Y won't be used...there's no cooling in this system.  The G terminal will go to the fan control, but before I commit to that...I'm confused by what appears to be 4 wires going to the blower area through a plain metal hole (what you called the bulkhead)  in your latest picture dscf0066-jpg and what I thought was the same thing showing 5 wires going through a thick piece of thermal insulation in dscf0050-jpg.


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## bill1 (May 29, 2020)

the other reason I think we need details on the heater contactor is to ensure the relay won't draw more current than your chosen thermostat can handle.


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## chopsaw (May 29, 2020)

24 volts is 24 volts . Amp draw from elements does not affect that


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## bill1 (May 30, 2020)

chopsaw said:


> 24 volts is 24 volts . Amp draw from elements does not affect that


I was referring to the VA, volt-amps, or power, of the coil, and whether the transformer had the power to drive it and if the thermostat had appropriate current ratings to handle it.  Obviously an 800A contactor has beefier contacts than a 1A relay, so the solenoidal coil that _moves _them will be sized to require more power.  
That said, the HVAC world appears to have settled on a cheap contactor design called Definite Purpose.  The case style and mounting feet of the DP Compact models appear to be what Dave has.  The leads to the coil are down low on opposite sides, with two (connected) male spades on each side.  (Which answers one of my questions.)   Although DP Compacts only go to a rated current of 40A, that is for motor loads and the beefiest Eaton C25 is rated for 50A into purely resistive loads, which is what the filaments (elements) present.  I'm hoping that's what Dave has.  
And looking at Eaton's coil characteristics, they're all 8 VA within that family regardless of contact rating and coil voltage.  (On the other hand, the beefier "Special Purpose" contactors of similar switching capabilities have 50 VA coils.)  
24VAC appears the standard control voltage in residential HVAC so no surprise there.  That looks like about a 12W transformer (need to confirm) so we should be ok, though not a lot of margin.  And this stuff all seems to fit together well (it would cost a fortune for the average homeowner to service it otherwise)  so most home thermostats can probably handle 1/3-amps of control current to the white wire as well.


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## daveomak (May 30, 2020)

JC in GB said:


> I looked up the technical specs on your cooler unit.  The bad news is that your unit uses a split phase motor that is not easily subjected to speed control.
> JC



It's a heater furnace only...  No AC....


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## daveomak (May 30, 2020)

What is . "FLA,  LRA,  & RES"


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## daveomak (May 30, 2020)




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## daveomak (May 30, 2020)

I'm trying to get the stuff you guys need....    What did I miss ???


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## daveomak (May 30, 2020)

Morning again....  it's time to cut hay ...    It's waist high... Soooo, I'll be in my outdoor office most of the day...
On SECOND THOUGHT...    Where did that come from ???


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## chopsaw (May 30, 2020)

daveomak said:


> What is . "FLA, LRA, & RES"


Full load amps
Locked rotor amps
RES , resistance ( I think ) That's what the coil should read in ohms
Numbers used to trouble shoot the unit I believe .


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## daveomak (May 30, 2020)




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## zwiller (May 30, 2020)

Is the cabinet/air handler a Goodman MBR1200?  

http://igate.northernplumbing.com/manuals/goodman/mbr.pdf


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## bill1 (May 30, 2020)

chopsaw said:


> Full load amps
> Locked rotor amps
> RES , resistance ( I think ) That's what the coil should read in ohms
> Numbers used to trouble shoot the unit I believe .


Agree with FLA and LRA.  I'm pretty sure RES is the constant (on) current rating for a purely resistive load, so 50A, which is sized correctly for 10kW filament-based heaters.  
This is a perfect contactor for the job.  Let me digest the other stuff after I mow my _own _hay.


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## daveomak (May 30, 2020)

MBR 0800 HKR10


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## bill1 (Jun 4, 2020)

daveomak...are you home free on this now or are there still loose ends?  Zwiller's link to the 2011 manual I think is closer to what you have than the manual pages you posted earlier (and are now down.) 

I've found ~4 different manuals for this covering about a 10 year span so we should have all the info you need.  Knowing about how old yours is might be useful...did you inherit it, find a close-out floor model, or ...?


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## daveomak (Jun 5, 2020)

It's purchased new a few months ago....


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