# Cabinet unit heaters



## WronGun (Oct 18, 2013)

We are replacing them with 3phase/480V units 


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## btharmy2 (Mar 11, 2017)

When heating a stairwell, the heater should be at the bottom, not the top. If you are installing new 3 phase, 480v circuits to feed the new heaters anyway, is it an option to put them at the bottom? That would heat much better. The electrical load for the old heaters was low because it was only for the fan/blower. We typically install a Dayton or Q-Mark fan forced wall heater on the first floor and allow the heated air to rise. I have never needed a 3 phase, 480v circuit for a stairwell heater. That is a lot of power for a heater.


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## WronGun (Oct 18, 2013)

btharmy2 said:


> When heating a stairwell, the heater should be at the bottom, not the top. If you are installing new 3 phase, 480v circuits to feed the new heaters anyway, is it an option to put them at the bottom? That would heat much better. The electrical load for the old heaters was low because it was only for the fan/blower. We typically install a Dayton or Q-Mark fan forced wall heater on the first floor and allow the heated air to rise. I have never needed a 3 phase, 480v circuit for a stairwell heater. That is a lot of power for a heater.




Yes , mark-q is what I’ll be ordering. These are in the stairways of a very fancy church. The roof in both stairwells goes up around 60’ as it’s one of a few steeples on the building. They are currently all in the ceilings and blowing down. 

We have 480v close by so we will use it. It’s actually just about as powerful as the current 30,000 BTU Units 


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## splatz (May 23, 2015)

I'm getting 14*30,000 btu/hr = 420,000 watts for equivalent heating power. If I calculated that right, that's a considerable amount of juice. 

Of course that doesn't mean that's actually what you need, they were probably way more that what was actually needed. 

An engineer could calculate the heat load, that would be an educated guess. 

To me a four story stairwell with a steeple on top is outside of what I'd be OK guessing at. 

So I might bring in someone I trust to do the heat load calculation, and if I have to pay them, I'd want that from the customer - that wouldn't be part of a free estimate. 

But in this case, just my experience, I wouldn't want it that bad - I haven't had good luck with churches as customers - so I'd tell them to get the heating load and size the heaters to THEIR specification. That way if it's not enough, it's not on me. It might wind up that the person they bring in to do the heat calc winds up getting the job, but I'd be OK with that in this situation - they earned it.


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## WronGun (Oct 18, 2013)

Maybe my calculations are wrong ?

1000 W=3412.141633 BTU/hr

This is a 480V/12A 10KW Heater 

I wouldn’t feel comfortable sizing it but all I’m doing is matching what’s there which worked very well for them. 

There are 2 in each stairwell 

I’ve had great success with the temple/church Market in my area this year 



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## WronGun (Oct 18, 2013)

My mistake , your figuring all 14 in the stairway.. 

No they are spread out to multiple stairways , and lobby areas.... this place is a massive compound 


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## splatz (May 23, 2015)

Watts per 30k BTU: 
1 BTU/hr = 0.29307107 W 
30,000 BTU/hr = 30,000*0.29307107 W = 8792.1321 W

So 14 30k BTU/hr heaters 
14 * 8792.1321 W = 123089.8494 W 

But now thinking about it 
30,000 * 14 = 420,000 BTU = like triple a normal sized house furnace 
So there just had to be a LOT of excess capacity there. 

Sometimes you'd just match existing, knowing that's safe, but in this situation that's going to overspend by a fortune. 

But you can't use existing to size the job, so you're back to square one, guessing.


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## splatz (May 23, 2015)

WronGun said:


> My mistake , your figuring all 14 in the stairway..
> 
> No they are spread out to multiple stairways , and lobby areas.... this place is a massive compound


That makes much more sense!


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## splatz (May 23, 2015)

WronGun said:


> Maybe my calculations are wrong ?
> 
> This is a 480V/12A 10KW Heater
> 
> ...


I was thinking 10KW per stairwell is the number is the number I would have guessed if I had to guess!


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## Cow (Jan 16, 2008)

splatz said:


> I was thinking 10KW per stairwell is the number is the number I would have guessed if I had to guess!


Wait. What?:biggrin:


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