Old 09-25-02, 04:42 PM
Visiting Guest
Posts: n/a

I have a Tempstar Model NUGK 075DC09 FURNACE. It is a 75M BTUH (INPUT) 3 burner unit. I want to de rate it to 60M BTUH input.It has #42 orifices in the manifold. According to my calculations I would have to change to #45 orifices to arrive at 60M BTH input. Am I correct in that? Also do you know of a source where I could puchase orifices? It seems around here nobody has them and-or willing to bother ordering them .

Old 09-26-02, 12:42 AM
lynn comstock
Visiting Guest
Posts: n/a
Changing the orifices (or any other part on your furnace) without the manufacturer's blessing, will remove the AGA safety certification...because the changed configuration is UNTESTED. There may or may not be safety considerations. Go the Tempstar (not a dealer) for parts and approval, or do nothing.
Old 09-30-02, 06:44 PM
54regcab's Avatar
Join Date: Jul 2002
Location: Oklahoma City
Posts: 661
Received 0 Votes on 0 Posts
Angry Yet another HVAC contractor screws the pooch

When are these HVAC contractors going to get thier head out of thier a$$ and start sizing these units properly to begin with ??

If the unit is an older model replacing it with a CORRECTLY SIZED new unit will save you big $$$ on your power bill.

As far as derating, all the attemts I have made have just resulted in lower efficiency and higher gas bills.
More comfort yes, but higher bills

In the last 3 homes I have lived in, the HVAC units were over twice the size required by manual J calculations.
Old 10-01-02, 04:17 AM
Jacque Schidt
Visiting Guest
Posts: n/a
Re: Yet another HVAC contractor screws the pooch

If this is an induced draft furnace, you will need to derate the inducer as well as the orifices. In addition, you'll beed to change the blower to a slower speed to make sure you don't overcool the gases, creating corrosive condensate.

In my opinion, there is no safe or sure way to derate a furnace.

Here is some info from the professionals:

You might (as Lynn recommended) contact the manufacturer and ask them for their engineered solution, but I will be surprised if they give you any hope.

Thread Tools
Search this Thread
Ask a Question
Question Title:
Your question will be posted in: