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Old 01-06-2018, 09:47 AM   #1
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Default Cabinet unit heaters

I need to replace 14 cabinet unit heaters for a client...

The current units were hooked up to a boiler system which was removed but heaters are still in the ceilings. They are heating up 4 story staircases.

Problem is the old heaters were 30,000 btu and used only 2 amps of electricity each. We will be adding a considerable draw to building load.

Is there any other effective way to heat up stairways. All they really care is that the temp doesnít fall below 50 in these areas.

Ideally , would like to use the same ceiling openings





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Old 01-06-2018, 11:04 AM   #2
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We are replacing them with 3phase/480V units


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Old 01-08-2018, 07:16 PM   #3
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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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Old 01-08-2018, 07:42 PM   #4
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Default Cabinet unit heaters

Quote:
Originally Posted by btharmy2 View Post
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 Iíll be ordering. These are in the stairways of a very fancy church. The roof in both stairwells goes up around 60í as itís 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. Itís actually just about as powerful as the current 30,000 BTU Units


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Old 01-09-2018, 06:48 AM   #5
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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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Old 01-09-2018, 08:05 AM   #6
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Default Cabinet unit heaters

Maybe my calculations are wrong ?

1000 W=3412.141633 BTU/hr

This is a 480V/12A 10KW Heater

I wouldnít feel comfortable sizing it but all Iím doing is matching whatís there which worked very well for them.

There are 2 in each stairwell

Iíve had great success with the temple/church Market in my area this year



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Old 01-09-2018, 08:17 AM   #7
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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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Old 01-09-2018, 08:19 AM   #8
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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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Old 01-09-2018, 08:20 AM   #9
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Quote:
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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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Old 01-09-2018, 08:22 AM   #10
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Quote:
Originally Posted by WronGun View Post
Maybe my calculations are wrong ?

This is a 480V/12A 10KW Heater

I wouldnít feel comfortable sizing it but all Iím doing is matching whatís there which worked very well for them.

There are 2 in each stairwell
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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Old 01-09-2018, 10:18 AM   #11
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Quote:
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I was thinking 10KW per stairwell is the number is the number I would have guessed if I had to guess!
Wait. What?
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