Horizontal furnace in the foundation crawlspace

[lewens]

Originally Posted by bkelly2

Jae, try not to make more out of it than there really is. Compress a gas or liquid and it gets hot, evaporate a liquid or expand a gas and it gets cold. When you think about it, it is quite simple. If it was as complicated as many here make it out to be, it would cost a lot more to buy, operate, and maintain. You can't swing a stick here in AZ with out hitting an HVAC guy.

Run this buy me one more time. To evaporate a liquid it requires heat.
Larry

[Charley L. Bottger]

Originally Posted by cbottger

Ok guys here we go I am going to spell out what I do as an Hi to inspect a A/C system and why I do what I do. I am not a PE or anything close but I have been working in this field since mobey dick was a minnow.

With the unit running I take the temperature from the registers and the return air temp as my very first item. Why because I don't care what the temp at the discharge from the A-coil is at this point I want to know what the temp is that is available for cooling the home. Its called duct loss between the coil and the registers more duct loss in the attic than in the floor due to extreme temperatures makes sense to me. I check for air volume at the registers and if I have a good TD between the supply registers and the return air 16 to 20 with good air volume I store this in the memory bank until we view the furnace and ducts if they are in the attic or in the crawl space.

I check visible wiring in the furnace for evidence of burnt wires. I view what ever part of the heat exchanger usually just the bottom for rust build up and I check the flame in heat mode for color and roll out on the older type of open burners. I check the blower wheel for lint build up as this will tell me if the A-coil is matted over with lint. I perform a CO test on the heat exchanger if present.
In this area with ducts in the slab I look for signs of water in the ducts. With ducts in the attic or the crawl space I want no bare metal showing and If flex is used I want to see no inner lining. I Check for air loss where the ducts connect to the plenum and for separated duct any where between the plenum and the registers. The return ducts if used should be completely sealed I do not want to draw in any un-conditioned air. The suction line should be insulated especially above a finished wall.

The condensate drain line should not be hard piped to the sewer main (air gap required) and it does not matter if there is a P-trap installed or not if it is hard piped to the sewer line you will get sewer gas into the air stream on a up flow furnace because the water will evaporate from the trap in the heat cycle. If the furnace is installed in a attic it is required to have a secondary drain pan under the coil with a secondary drain that enters a visible area from the ground level.

On electrical furnaces and strip heat on heat pumps I use a amp meter to ensure all of the multiple strips have amperage draw with the stat in the high position just in case there is a two stage stat for bringing on all of the strips.

I check the name plate data for tonage and age and the MFG's recommended breaker size and ensure that the breaker size has not been exceeded or undersized. I check the condenser fins for lint build up and physically touch the suction and liquid lines at the unit while casually checking the size of these lines.

I do not consider this as an in depth or micro evaluation of the system. Checking TD at the registers has served me well as a HAVC person and as a HI I don't think I will be changing my mind in the near future.

RR you need to close all of the windows and doors if you are getting TD's as described above

Sorry guys I was in a hurry yesterday and left out the last check I do on a gas fired furnace (older type) that I would guess that a lot of HI's miss.

After I turn the stat back to below set point and the burner extinguishes I stay in the general area of the furnace or at least close to a register so that I can determine if the bimetal temperature controled combination fan and limit switch does indeed shut down the blower motor. These switches are adjustable and are normally set to turn off at 100 degrees. In a lot of past inspections I have found many of these switches that just run to infinity and need to be changed. I do not check the operation of the limit side of this switch as it would require shutting down the blower with the burner in operation and I consider this as beyond the scope of a normal home inspection.
Hope this post has helped at least one person




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[Charley L. Bottger]

I wanted to expand on a statement that I made concerning the checks that I perform on the older type gas fired furnaces. I stated that I do not check the limit switch. What I should of stated was I do not check the high set point of this switch by turning off the fan blower and checking what temperature this switch opens at thus shutting down the gas valve. My checks are all performed strictly by operation from the thermostat.

What I do check concerning the limit switch is premature opening of this switch during normal operation. This switch normally opens in the area of 200 degrees at the heat exchanger. I usually average 2 to 4 furnaces a year that the limit switch is malfunctioning and this is determined by simply observing the furnace to ensure the burners are not cycling on and off before the set point of the thermostat is reached. This is something that I consider very easy to overlook and is probally missed by many inspectors.
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[Russel Ray]

Originally Posted by cbottger

I stated that I do not check the limit switch. What I should of stated was I do not check the high set point of this switch by turning off the fan blower and checking what temperature this switch opens at thus shutting down the gas valve.

Huh? You lost me.

Originally Posted by cbottger

My checks are all performed strictly by operation from the thermostat.

Now I'm back.

Originally Posted by cbottger

What I do check concerning the limit switch is premature opening of this switch during normal operation. This switch normally opens in the area of 200 degrees at the heat exchanger.

You lost me again.

Originally Posted by cbottger

I usually average 2 to 4 furnaces a year that the limit switch is malfunctioning and this is determined by simply observing the furnace to ensure the burners are not cycling on and off before the set point of the thermostat is reached. This is something that I consider very easy to overlook and is probally missed by many inspectors.

Sounds like you're talking about "short cycling." By the time the Clients have told me that it's too hot, the furnace has been running about 20 minutes or so. If it's short cycling, one will know within 5-10 minutes, usually much sooner, so if the furnace cuts off without me turning it off, I check to see if someone has turned it off rather before asking me or telling me that it's too hot. If it's still on but the temperature is not the 98° that I set the thermostat at, then I probably have short cycling occurring.

[Keith Swift, PhD.]

I wrote about the way reporting on "a leaky faucet" has evolved over the years, as we attempt to better protect ourselves. However, I heard it first in a seminar given by Bob Pearson, of Marion Allen Insurance. The story has the virtue of being funny, very real, veryu serious, and very educational. P.S. I'm trying to persuade Bob to do a seminar with me on avoiding litigation for NACHI, and hope he'll take me up on it. It'll be interesting.

[David A. Andersen]

Jae, try not to make more out of it than there really is. Compress a gas or liquid and it gets hot, evaporate a liquid or expand a gas and it gets cold. When you think about it, it is quite simple. If it was as complicated as many here make it out to be, it would cost a lot more to buy, operate, and maintain. You can't swing a stick here in AZ with out hitting an HVAC guy.

Brian, I posted a question on another thread you authored:

Quote:
If anyone is promoting the concept of taking a temperature difference with a dry bulb thermometer (we'll leave out the infrared thermometer debate) to determine operation of HVAC equipment, I pose a question.

Fact: HVAC equipment, as posted is all about transferring heat.

Fact: heat is measured in BTU.

Fact: to lower the temperature of air, BTU must be removed from that air.

Question: how many BTU's is in 1 pound of air at 70°F?

Question: how many BTU's is in 1 pound of air at 60° F?

Question: how many BTU 's were removed from the air to lower the temperature from 70°F to 60°F?

You, nor anyone else attempted to answer this "Simple" question.
Why. was it too SIMPLE?

The fact of the matter is that HVAC is so damn backwards (as Jae posted) that few (to include seasoned HVAC Vets) understand the true operation of what is really going on.

If you would like to stick to this thread, how about explaining the simple process of "Dynamic Loss" or the effect of "Apparatus Dew Point" on the temperature split. I would like to expand this subject to cover the Sensible Heat Factor and By-pass factor of evaporator coil design and a few other simple processes that apply. But, that subject may be too elementary and bore too many folks to discuss!?

[Charley L. Bottger]

Originally Posted by dandersen

Brian, I posted a question on another thread you authored:




You, nor anyone else attempted to answer this "Simple" question.
Why. was it too SIMPLE?

The fact of the matter is that HVAC is so damn backwards (as Jae posted) that few (to include seasoned HVAC Vets) understand the true operation of what is really going on.

If you would like to stick to this thread, how about explaining the simple process of "Dynamic Loss" or the effect of "Apparatus Dew Point" on the temperature split. I would like to expand this subject to cover the Sensible Heat Factor and By-pass factor of evaporator coil design and a few other simple processes that apply. But, that subject may be too elementary and bore too many folks to discuss!?

David Please
Let the sleeping dog lye you are getting to deep for this board
I do not consider Hvac as backward,scientific or complicated just a simple pressure/temperature releationship.
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[Charley L. Bottger]

Originally Posted by rray

Huh? You lost me.


Now I'm back.


You lost me again.



Sounds like you're talking about "short cycling." By the time the Clients have told me that it's too hot, the furnace has been running about 20 minutes or so. If it's short cycling, one will know within 5-10 minutes, usually much sooner, so if the furnace cuts off without me turning it off, I check to see if someone has turned it off rather before asking me or telling me that it's too hot. If it's still on but the temperature is not the 98° that I set the thermostat at, then I probably have short cycling occurring.

RR

Short cycling is a good choice of words.

Point being how many inspectors stay in front of the furnace to determine this. If the burner cycles on and off enough it will eventually reach set point of the stat.

[Bruce M. Graham]

Not if it is cycling due to tstat anticapator(older stats not eletronics).

[Charley L. Bottger]

Originally Posted by bgraham

Not if it is cycling due to tstat anticapator(older stats not eletronics).

Bruce

The anticapator has notta to do with cycling the burner unless set point was reached as they were designed to do exactly as their name indicates. (Anticapate) Energize the gas valve approximately 2 degrees below set point. If you have a burnt out Anticapator you will have no flame the gas valve will not open.
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[David A. Andersen]

What are we talking about here Charley?

(Anticapate) Energize the gas valve approximately 2 degrees below set point.

The anticipator heats up when the thermostat calls for heat (it is otherwise un-energized).

It can not energize anything if "it" is not energized.

The "anticipation", is when you get close to set point while the unit is running. Anticipating the approaching set point. It's job is to make the t-stat reach set point before the room temp actually gets there. This prevents the furnace overshooting the set point (Due to the delayed reaction of the produced heat from the furnace reaching the t-stat location).

If you have a burnt out Anticapator you will have no flame the gas valve will not open.

Also, if it is not set correct it will "short cycle".
The anticipator overheats and shuts down the t-stat prematurely. Once off and the anticipator is off, the t-stat cools quickly (from the cold room temp) and the furnace comes right back on.

It appears this is another one of those "backwards", it's not what you would expect HVAC things!?

I do not consider Hvac as backward,scientific or complicated just a simple pressure/temperature releationship.

[Charley L. Bottger]

David we were originally talking about short cycling the furnace burner on a limit switch that was opening premature and some how the stat got brought into play.

Yes the heat anticapitor setting has to be matched with the amp draw of the gas valve or it will not maintain temp close to stat setting but in my thinking this is not a true short cycle in relation to the short cycle from a bad limit switch as the anticapitor will cycle the burner and the blower where as the limit switch being in the air stream of the blower cools much faster than a heat anticapitor at the stat. Most of the time the blower will not have shut down on its fan switch before the gas valve re-opens.

Lets just pick some numbers the normal operating range for a fan switch on the older furnaces say closes at 110 degrees and activates the blower motor. In the mean time the limit switch is factory set at say 200 degrees but this switch decides its going to open at say 115 degrees it shuts down the gas valve thus no flame but the blower is still running because it does not shut down until say 90 degrees in the mean time the limit switch has cooled enough to close the circuit and re-active the gas valve creating a short cycle of the burner that Mr. home inspector does not observe because he was not squatted in front of the furnace watching the flame he was back in the hall somewhere waiting to hear the blower shut down giving the false impression that the furnace was performing as intended

David I don't know what I was rambling on about the heat anticapitor some times I don't proof read what I am spouting about. Sorry.

[David A. Andersen]

That is correct.

Also, we should note that some furnaces may cycle (shortly ) when tested in the summer because of the hot weather associated with an assortment of other things. The furnace may otherwise operate correctly during the heating season.

It's good to get all this "how it works" stuff out. Just for a better understanding for all. I just don't want misinterpretation sending someone down the road to get in legal trouble.

I had a local TVA Inspector inspector testing a furnace install that a company just installed. It was 98 degrees outside at 6:30 pm. The furnace was short cycling and he was not going to pass it till it would run without cycling. I forgot what the temps coming out were, but it was close to a blast furnace! I was called in by Trane to trouble shoot. I ended up changing the limit switch to a 300 degree until the inspector left!

Some things are just not meant to be!

[Brian E. Kelly]

Typically building heat gain is calculated in tons of refrigeration needed:
· 1 ton of cooling is the amount of cooling provided by melting 1 ton of ice over a 24-hour period.
· 1 ton of cooling equals 12,000 British Thermal Units (BTU) per hour.
· It takes 1 BTU to raise 1 pound of water 1oF.
· It takes approximately 1160 BTU to evaporate 1 pound of water.
· It takes 0.24 BTU to raise 1 pound of air 1oF.
· One pound of air occupies 13.7 cubic feet of space at sea level when the temperature is 75°F.
· Removing 1 ton of building heat requires cooling 570 cubic feet per minute (CFM) of room air from 75°F to 55oF at sea level.
· Removing 1 ton of building heat requires cooling 660 CFM of room air from 75°F to 55oF at 5,000 feet in elevation.


I believe if you move the decimal place one spot that would answer your BTU question David. I could give you the answer in Joules or calories if that would be better.


Now after reading many posts here I have seen the light, HVAC is one of the most complicated sciences known to mankind. In light of such facts and after much research, I have concluded that HVAC is so complicated that there are no recorded events of homeowner complaints with either heating or cooling of residential homes, because mere homeowners do not posses the knowledge to tell if their system is working or not working.

Thank you gentlemen.

Oh yea Larry, heat produces perspiration, which leads to evaporation, and you cool off.