# Combustion testing



## JohnH1 (Jun 6, 2009)

1st Do any of you use combustion anilyzers on every clean and tune. We are sending more of our tecnitions to get certified in combustion. We are concidering offering a higher end tuneup and including combustion test and adjustment along with static psi / airflow check and adjustment. 2nd Does anyone else offer this as a option on a regular basis.
3rd. do you think the anilyzer should be a company supplied tool? We are going to supply them for now but they are costly and everyone knows if they did not pay for it they dont take care of it as well.

John


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## beenthere (May 30, 2009)

When you do a tune up on an A/C or heat pump. Do you charge the customer extra if your techs put their guages on the system?

How can you tune up a gas or oil fired unit if you don't use a combustion analyzer on it?

Offering it at an additional charge is like saying. "Hey we don't really, and haven't been really tuning your system over the years, but if you really want what you were paying for all along. For another XX dollars, we'll do it".

A CA used right can be a profit making tool.

What classes/who's classes are you sending your people to?

Yes, they are expensive. But, should be a company tool. That way you can track if the CA's are up to date with their calibrations.

Assign one to a tech, and have them sign for its general care. And have on the form that they are responsible for damages from mishandling of them.


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## JohnH1 (Jun 6, 2009)

I guess I mis-stated a little. We do plan on doing the combustion on the cleanings. I was looking at more the airflow diognostics and adjustments. 
Now that you put it that way even the airflow should be checked and adjusted to really call it a full tune up. 
Maybe like lawn maintiance companys do. On new customers they charge a higher price on the 1st service to get everyting in shape and then the weekly service is cheeper because now it is not as much work to maintain.
We could do the same the 1st furnace or A/C tune up is higher $ to get everthing in proper operating condition. But on the yearly maintiance program it would be cheeper. The innitial full tune up on a gas furnace with combustion, air flow and everything else that goes along with it could take up to 2 to 3 hrs. This could be a incentive to join the maintiance program. and if they mis a year or two they would have to redo the full price job.
We are doing our training through National Comfort institute. http://www.nationalcomfortinstitute.com/


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## beenthere (May 30, 2009)

I find a quick CFM check is all you need to do. To get some good sales opportunities.
A CFM check by static pressure can be done in less then 5 minutes on most air handlers.
Some furnaces will require 10 minutes(getting between coil and furnace can slow you up).

By tracking the static pressure of the air handler, and or the pressure drop of a eavap coil on a furnace. Can tell you if the coil needs cleaned or not. And save you time from having to open up the case coil to check it visually.

Many customers won't want to do the alterations/repairs to their duct systems.
So you have to be careful how much extra you charge for it on a tune up/SA call.

After you learn how to determine a systems capacity at the current operating ambients. You can start pushing the duct improvements after you track the system for 2 or 3 years.

NCI is a good course/org to take classes from.
I don't agree with everything they teach. Specially when they teach you how to come up with a 50 to 60% efficiency on a unit.

But what the combustion reading mean, and how to correct those conditions will prove very valuable to you and your techs.



PS: Don't jump when the trainers throw and or drop their meters on the floor.


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## JohnH1 (Jun 6, 2009)

Myself and my brother went through training both combustion and air dignostics last year. Very eye opening. 
Now that we are both comfortable with the process we want to bring everyone else up to speed. I know we are behind the curve on this training. 
I guess it is just going to be a learning curv for us to get it down smooth. I know when I tune and adjust even our new installs it can take some time. checking static vs blower chart and temp rise then re checking everything again after chainging blower speeds. 
I dont have a flow hood yet but I did just get cheeper hot wire. I just dont think the blower charts are close on some equipment. But I just got the tool so now I will be able to compair the blower chart to the hot wire annonometer. Flow hood will be next I am just being to cheep to get one yet.


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## beenthere (May 30, 2009)

Static pressure checking is best done by averaging, the same as using an anomometer.

You'll find that static is pretty close. if you check it against temp rise on air handlers with electric heat, and check it against the temp rise.

An anomometer, won't tell you what the blower is moving. But how much the duct system is or isn't delivering. Which can be good for selling duct sealing work.


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## JohnH1 (Jun 6, 2009)

beenthere said:


> An anomometer, won't tell you what the blower is moving. But how much the duct system is or isn't delivering. Which can be good for selling duct sealing work.


I think you are talking about a vein anomometer or flow hood at the register. (correct?) I guess the hot wire can be used at the register also.

The Hot wire anomometer in the return drop will give the cfm of the blower With minor leakage between the equiment blower and test holes. 

Avg fpm x sqft = CFM If I rember correctly. Then I can go to the registers to see if I am sending and returning full cfm from the space.

I am at this point mostly tring to confirm proper cfm at the equipment especilly for a/c since the heat cfm can be figured fairly close with temp rise that is assuming proper gas input has been confirmed.

Very few of our customers are interested in duct renovations due to the cost.
Heck I have been having a few more customers using us for diognostics and declining the repaire to do it themselves.
I hope to get more into renovations as the economy recovers.

As you said it should not take to long. I am just still a little slow as time go on we will get quicker. It is getting to the point we will have to make several trips back and forth to the truck just for tools just to do a basic furnace tune up.


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## beenthere (May 30, 2009)

You can use a hot anemometer in a duct or for registers.
in teh duct work, you have to average the same as with the hot anemometer.

Duct alterations don't have to be expensive.

A helper duct can eliminate a lot of problems. And doesn't cost a lot.


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## JohnH1 (Jun 6, 2009)

Helper duct? Are you talking about for example a 8" rnd from the plenum and reconnect further down the trunk line?


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## beenthere (May 30, 2009)

Except it usually takes a larger size then 8" though. And often its better to run it to the end of the trunk line.


But, that will eliminate a lot of poor air flow problems on undersized returns.

Got a duculator handi?


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## JohnH1 (Jun 6, 2009)

yep got one


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## beenthere (May 30, 2009)

Ok, double check my CFM and FPM to your duculator. And I think you'll see what I mean in the following.

Take a 3 ton system. Supposedly it was designed to move 1200 CFM.
You find out its only moving 850 CFM. And of course it has poor air flow to the end supplies..

They started off with 8X22. that’s about 1080FPM, when moving 1200CFM. But since its only moving 850CFM, its actual FPM is 950.

Since your 350 CFM short of what you want to move. Find on the duculator, the smallest duct that will move 350CFM at the same velocity(950) that the duct system is already moving .

You’ll see that 8” is just shy. Which means you need to go to the next size up.
Reason why. When you add this duct, the static pressure will drop. And the 8X22 will move a little less air.

When you tap into the end of the trunk line. Somewhere near the last 3 to 4 supplies ). 
You will provide air flow to those supplies from the helper duct only. Lowering the CFM that the 8X22 has to carry, Which decreases the static at its beginning. And will lower the CFM to the first supplies. Helping to even out the homes temps.


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## JohnH1 (Jun 6, 2009)

Cool
Never really thought of that. Some times the simplest things are right in frnt of you. I am always looking at changing the hole duct run. 

Latly I have been finding ther are not even enough registers to handel the required cfm of the high efficiency furnaces. The homes around us are so poorley insulated if any at all the equipment needs to be usualy one size bigger than it should be. I should get into insulation biz to be able to use the systems that are in the homes.

But that is another topic.

Thaks for the tip. There is always something to learn you just have to listen.
John


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## beenthere (May 30, 2009)

No problem.

when you do a helper duct like that.
What you'll find in reality. is that the helper will actually move more air then you planed on. Which is a good thing. keeps the noise down on the existing trunk line, and keeps the velocity up on the helper.

We all tend to make it harder then it needs to be. Until we're shown the easier way.

Also. using that method. if the trunk is grossly undersized.
You would then tap into the trunk line at say the half way point, and near the end.

EG: If that 8X22 in the example was used on a 3.5 ton system. You might end up using a 12" round, and then tee the 12" so a 10" feeds into the middle of the trunk line run, and between the last 3 or 4 supplies. 

Of course. you still need the return air improved if its also grossly undersized.


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## beenthere (May 30, 2009)

If you have a forced air system at your house.
And feel like trying a simple not harmful test. :laughing:

Take your static pressure reading of your supply and return.
Then. Disconnect 1 supply branch near the furnace/air handler, 1 in the middle of the trunk line and 1 on the end.

Then recheck your return and supply static.
If you have a regular PSC blower. the return will have increased about the same amount that the supply decreased.

If you have a VS blower. only the supply static will have changed. if it was moving the CFM that it was set to when the supply branches were connected.


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## JohnH1 (Jun 6, 2009)

I can see that. The decreased static on the supply side will increase the total cfm and now the return has to move more air increasing the static. IE: if you change one side of the system you need to possably improve to other side.


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## beenthere (May 30, 2009)

Yep. that does happen often. But sometimes you get lucky, and the return is short. And either it can pull enough without being loud. Or, you can run a larger size duct without too much trouble.

Sort of have to evaluate both before making any changes. or they will call you back and say. it wasn't loud before you worked on it. so you did something wrong. And we shouldn't have to pay for your mistake.


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## JohnH1 (Jun 6, 2009)

Beenthere
Following the same idea of the helper duct. What about adding a bypass around the evap durring the winter. This would take additional static off the blower and could help out a lot with the 95% furnaces since the require more air flow than the a/c a lot of the time. Also lowering electrical usage of the blower.
It would require the coil to be placed a little higher from the furnace but that is good anyway. And the bypass would need to be a good seal in the summer. A example of a damper is here http://www.hvacsolutionsdirect.com/product.php?productid=417&cat=337&page=
It should not be to costly if done durring the innitial install of a new furnace. 

What am I missing this seems like one of thoes ideas that has eluded me yet is simple. Sometimes this sh** wakes me up at night.


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## beenthere (May 30, 2009)

That would be a solution/bandaid for an oversized furnace.
Since what ever air is bypassed, is air that is not being delivered to the house. It is reducing BTU delivery to the house.

A 6" bypass would bypass roughly 180 CFM. At 50° temp rise across the heat exchanger. You would be lowering BTU delivery to the home by almost 10,000 BTUs.
An 8" will bypass over 400 CFM, at 400 CFM and a 50°F rise across the heat exchanger, you would be lowering BTU delivery to the house by over 21,000 BTUs.

So in either of the above examples. if the house was heating ok at design conditions with a bypass like that. the furnace is over sized for the homes heat loss.


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## JohnH1 (Jun 6, 2009)

I mean a bypass around the evap to reduse static. IE a 6" Duct connected under the evap and then re connect above the evap. Just not forcing all the air through the evap. Allowing some of the air a easer path around the coil.


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## beenthere (May 30, 2009)

Hard to say if that would help a lot or not.

Although the coil is a pressure drop/resistance to air flow.
Would a 6" bypass configured like that move more then 100 CFM is the question.

The answer would be. Only if the coil was the only interference to air flow to the house.

As in. If you having trouble with the rooms on the end of the duct system. It wouldn't help. Since most of the extra air would be forced out the first supply runs. And very little would reach the far supplies.


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## JohnH1 (Jun 6, 2009)

I am mostly thinking of this to make it easer to move the cfm. Why work harder all winter and use more energy forcing all the air through a coil. 6" is only a example it could be any size square or round as long as it could seal tight durring the summer. There is more winter than summer here. I dont know what the energy savings would add up to but it couldnt hurt.

A over sized plenum with a removable slide on the overhang would work also. Kinda like winter / summer dampers when the old seperate watercooled a/c packages were used in combination with the furnaces.


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## beenthere (May 30, 2009)

A PSC motor uses less electric at higher static pressure then it does at lower static pressure. Because it is doing less work, since it is moving less air.


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## beenthere (May 30, 2009)

A 1 HP power motor under full load. In therory is moving 2481CFM. Ore, 33,000 pounds of air a minute.

Increase static pressure so that it is only moving 10,000 pounds of air a minute. And its only working as less then a 1/3 HP motor. And its amp draw will drop accordingly.


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## JohnH1 (Jun 6, 2009)

Assuming we are able to move the correct cfm through the evap on high speed oridginalyl but now with the lower static it can be done on med-high. Wouldent that be a lower amprage? 

On the other hand if we are now moving more air and drawing higher amprage. We would now be delivering more heat now that we are closer to designed cfm. This should make the overall operation more efficient shouldent it?


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## beenthere (May 30, 2009)

If a blower moves more air on med high speed then on high speed. It is using more wattage at med high then at high speed. Since it is doing more work.

1,000 CFM with a 50 degree temp rise is 54,000 BTUs.
800 CFM at a 62.5 degree temp rise is 54,000 BTUs.
600 CFM at a 83.4 degree temp rise is 54,000 BTUs.

Its the combination of CFM and temp difference that determines BTUs delivered.


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## dan22 (Dec 2, 2010)

*combustion analizers*

what makes and models do you people use, and have you had good experince
i am going with an E instrument is anyone useing this product, if so let me know if it is a good machine thank you


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## beenthere (May 30, 2009)

Bacharach Tech 60, and Infinite.

Don't know what a bad experience with one is. So I think I have only had good experiences with them.


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