Measuring Heat or AC Temps

[rkyfletcher]

I'm a new inspector and have been confused about something lately. Can anyone tell me the best or only areas to check the temperature output of the heat and AC? The register farthest away, the plenum, etc...I have had several inspectors tell me different areas. Any help would be appreciated.

[Brian G]

I check heat at the nearest register, AC at the nearest register and the return air grill. I haven't read of anyone doing much differently from that, but it wouldn't surprise me.

Brian G.

[DonTx]

I check temps and airflow at all registers to see if there is a wide swing in temperatures.

I either heard or was told that registers on the same zone should not have more than a 3 degree temperature difference. Anyone know about this? Any register with a temp difference of more than 5 degrees or a noticeable lack of airflow gets written up.

[rkyfletcher]

Brian and Donald, Thanks for your responses. I have also been checking the closest registers and the return. I haven't been checking every register like Donald, but I will as of now. He makes a good point. Being new in the business I want to do everything I can to do a good job and sometimes I still question myself when an "experienced" inspector tries to give me advice.

[RobC]

If you check the data plate on any gas burning appliance or others, you'll note something called bonnet temperature or bon temp.

The bonnet is really the location immediately downstream of the exchanger.

SO,

For any meaningful temperature discussions one should measure at the bonnet or plenum.

That's why I need to sharpen my awl.

Don't forget to carry 'band aids' (little squares of aluminum duct tape).

Ps. Don't assume the general temp difference is 50-80 as they all differ.

[Darren]

When checking A/C temps, I do it as close to the unit as possible. If I can, I find a small opening at a duct connection to inset the thermo (same with return, usually the plenum connection). Just make sure it not too close to the coil.

As far as temperature difference, depending on the length of run and amount of insulation, I would think the difference would vary (larger than 5 degrees).

I check every register (and baseboard or radiator) to make sure heat (or cooling) is present and air flow. I will note a decrese in flow if present.

Another check to consider (if a central return is present) is that the bedroom doors have the required undercut.

Darren

[Jim Katen]

Originally posted by rkyfletcher

I'm a new inspector and have been confused about something lately. Can anyone tell me the best or only areas to check the temperature output of the heat and AC? The register farthest away, the plenum, etc...I have had several inspectors tell me different areas. Any help would be appreciated.

RobC is right. I drill small holes in both the return and supply plenums close to the unit and insert my thermometers there.

The closest register is ok; it should be very close in temperature to the supply plenum. However, I always avoid using the return air grille. If the duct's leaky, your measurements will be useless.

- Jim Katen, Oregon

[Bill Kibbel]

I haven't punched a hole for probably 15 years. I got tired of being yelled at by sellers or listing agents. I use this:

www.professionalequipment.com/product_i ... roduct.jpg

The dual K-Type thermocouple probes fit in any gap or seam and it saves time by measuring the temp diff automatically. (I don't have to remember how to do subtraction)

[Jim Katen]

Originally posted by inspecthistoric

I haven't punched a hole for probably 15 years. I got tired of being yelled at by sellers or listing agents. I use this:

www.professionalequipment.com/product_i ... roduct.jpg

The dual K-Type thermocouple probes fit in any gap or seam and it saves time by measuring the temp diff automatically. (I don't have to remember how to do subtraction)

Cool gadget. Though, honestly, I can't remember anyone ever yelling at me for drilling these holes. I guess they just figured I knew what I was doing. (Ha! Laugh on them.)

I like the dual probes, but I'd hate for my subtraction skills to atrophy. It's bad enough that I've forgotten how to use a slide rule.

- Jim Katen, Oregon

[RobC]

Great little tool.

Something you wouldn't want to leave behind.

When I'm in the furnace room I usually punch the hole while my client is upstairs working the stat. I have never had any problems.

I always use the furnace cleaners plugs if they are available or access the plenum through the vibration collar.

[Brian G]

I didn't think to mention it but I also check all registers for air flow, but not for temps.

Brian G.

[rlskfoster]

Darren,

I didn't catch it the first time I read this post but I was "studying" tonight and I read the part about " bedroom doors have required undercut" with a central return. Could you expand on that. I have definately been in houses where the doors drag the carpet but I did not realize they should have a clearance to pull air. It makes sense though so you get circulation.

Buster

[Jim Katen]

Originally posted by rlskfoster

Darren,

I didn't catch it the first time I read this post but I was "studying" tonight and I read the part about " bedroom doors have required undercut" with a central return. Could you expand on that. I have definately been in houses where the doors drag the carpet but I did not realize they should have a clearance to pull air. It makes sense though so you get circulation.

Buster

It makes sense, it's a good idea, it does help to distribute conditioned air and I recommend it in my reports when it's lacking. However, it's not a "requirement." At least not in any published code or manufacturer's installation instructions.

- Jim Katen

[kteitel]

One way to think about it, the air enters the room through the duct and displaces the air already inhe room. If the door isn't undercut or there isn't a return duct, then the air has no where to go. The air won't get distributed evenly and the furnace gets choked.

One thing I do notice is if the system is having imporperly balanced, you will see a black line going across the doorway on the carpet. The air is forced under the door and the carpet acts like a filter. The black line is tough to get out.

Kevin Teitel

House-Pro Inspections

[MechAcc]

Allow the air conditioning system to operate a minimum of 15 minutes for taking temperatures. This will be even more important on newer units with higher efficiency ratings.

[chrisprickett]

We have mostly flex ducting out AZ way. I just poke a meat thermometer 4' from supply and return. I look for a delta of about 20 degrees on a/c.