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Joined on April 16, 2013

Last Post on July 25, 2014

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I Thought......

@ February 26, 2014 7:46 AM in Coil Material Opinions:

The blower has to overcome the duct resistance, plus the other pressure drops in the system, to deliver the designed air quantity. This is why many in the industry have the concept backward, residentially. You first have to find a blower that will deliver your required air, take out the PDs from your accessories, and use the remainder to calculate duct friction rate. A flex system will only increase the resistance against the blower, causing high energy use, noise, and substandard comfort, especially if distorted or not accounted for in the design.

UC Ducts

@ February 25, 2014 9:13 PM in Coil Material Opinions:

My comment was to TonyS (rip it) and was intended to be complimentary for recognizing the value of insulation. You mention two interesting issues: SEER and insulating ducts. First of all, if for example, your electric cost is $0.12/KWh and you have a 3-ton machine, a 14 SEER unit would cost $0.31/hr. while the 16 SEER model would be $0.27. Multiply that by cooling hours per season; you may find the small difference will make you feel better about not having room for the larger 16 SEER coil, and be better off having a well-performing duct system.

Flex duct moves 40% less air than sheet metal, so any distortion makes a bad situation worse; especially if flex was not considered in the original design. Compacting insulation lowers R-value. However, it sounds as if you are trying to do it right. I would check your ESP to see the effects any duct distortion has had on your blower.

Rip It

@ February 25, 2014 8:27 AM in Coil Material Opinions:

Your post certainly strikes a chord to those of us who advocate locating ducts in conditioned spaces, which I view as an underlying tone of your comment. In some applications, cost or physical limitations get in the way of doing the right thing; keeping ducts out of attics.

Your post also nods toward the value of insulation. Using your Delta T, a 6" duct would lose 15 BTUH per linear foot with R8 and 11 BTUH with R10, so if you aren't able to rip and tear then insulate, insulate, insulate.


@ February 20, 2014 1:12 PM in Coil Material Opinions:

Following all of the storm damage before Sandy, we had the now-famous "Chinese Drywall Era" which drove most manufacturers crazy. Hence, the movement to all aluminum coils, which appear to be less prone to off-gassing building materials creating champagne leaks in coil tubing.

R-8 duct insulation in non-conditioned spaces is code. However, check your local AHJ to see if they have a different requirement.

Wet AH

@ February 19, 2014 9:47 AM in Hydronic Air Handler in A Condo Issues

I'll bet my bottom dollar you have pressure issues. The PD of a hydronic coil can easily be .80 IWC. If this and other PDs were not considered during the equipment selection process, your duct sizes are too small. This results in noise, drafts, and poor performance. Have your contractor check the ESP!

Pressure Switch Test

@ February 11, 2014 7:02 AM in draft simulator

You can inexpensively obtain vacuum hose sections and plastic barbed tees from an auto parts house, which will put your manometer in series with the switch and gas valve or inducer. Pull the factory hose off the switch so you're not cutting tubing that requires a coupling to reconnect. You can also check calibration by pinching the tubing and tubing condition at the same time.


@ February 10, 2014 6:10 AM in manometer

Existing ducts are a different animal, since you weren't in the driver's seat. So now you determine your ESP and subtract individual pressure drops. The pressure left is what the blower "sees" as the distribution system. In most cases this will be sky high because the installer does not understand that you choose a blower FIRST, not that .10 IWC thing. The good thing is the system doesn't care where you relieve pressure. It is easier to do RA mods than SA in most cases.

CFM/ton is a RESULT of your calculations, NOT the basis for them. If your load is 22,000 BTUH sensible and 30,000 BTUH total, your target CFM is 852. You now have to find a blower that will give you that at hopefully not over .72 IWC when you add in your duct pressure from above and other components. Try to get your target on medium speed so you have room to adjust up or down.


@ February 8, 2014 4:13 PM in manometer

Oh yes, my fellow duct guru. I'm an ACCA blue blood. When I finally got the secret of comfort from them, I have never looked back.

In Jersey, I have found the housing stock to be reasonably well-constructed, so my latent loads are on the small side. This is great, because I can take a credit from the latent capacity of the machine I have selected and apply it to the sensible load. I love this because I can use smaller units and still neutralize both of my loads. With a light latent my CFM can hit 500+, yet I can still guarantee 75/50 on a design day.

Duct Design

@ February 8, 2014 10:39 AM in manometer

Using either static regain or equal friction is purely what you prefer, and I applaud your use of either. Here is the more important issue: before even thinking about ducts, you have to choose a blower that will provide the correct pressure to get the CFM required to the conditioned spaces, less the pressure drops of all components in the system. CFM is NOT 400 per ton; rather, it is the air needed to satisfy the sensible load gathered from your load calculations. For example, a low sensible load (high latent) requires a colder evaporator (low CFM), while a high sensible (low latent) needs higher air flow and you will have a warmer coil. This can be anywhere from 300 CFM to over 600 CFM per ton. Oddly enough, if you average CFM research from years of studies, the average is 400, so the manufacturers believe if you base air flow on this number it will "work" but it is rarely correct. Once you calculate the load-required CFM, you then pick a blower that will give you that amount at a decent pressure; try to stay within .50 to .70 IWC if you can. Once you back out your pressure drops (dampers, coil, filter, etc.) you have the pressure left for your duct design.


@ February 7, 2014 2:27 PM in Flue liner size for new gas water heater ?

I would be happy to send you a copy of the GAMA tables.

Power Vent

@ February 7, 2014 6:25 AM in Flue liner size for new gas water heater ?

You certainly got a bucketful of fabulous comments from Steve. Taking all of that into consideration, and not discounting his input in any way, there still may be a nod toward the PV. Venting is a serious business in which many contractors and building inspectors are not on top of their game. With the PV, the venting instructions are in the IOM, so you have pipe sizes, equivalency, pitch, connection requirements, termination configurations, and termination locations. As long as you follow the IOM to the letter you can't get hurt. With the atmospheric model, the maker assumes that you understand the GAMA tables and will vent accordingly.

The efficiency difference Steve mentions would indeed be the vent motor's consumption, yet his comment about combustion air (another life-safety issue most disregard) is more important than a few watts of power, assuming both atmospheric and PV tanks have the same 1st hour rating (how you size your tank) and energy factor (the higher the EF, the more "MPG").

Liner Sizing

@ February 6, 2014 9:12 PM in Flue liner size for new gas water heater ?

Never insulate a vent connector or a common vent section! Use the GAMA Tables for a single appliance to size your vent system. This is a life-safety issue and should not be taken lightly. Choose a liner that is stainless steel; the aluminum liners have a very short lifespan.

HP Operation

@ February 2, 2014 1:38 PM in York heat pump/auxilliary element heat

If you have installed a fairly sophisticated programmable thermostat, you can set parameters for heat pump and electric heat operation by choosing options in the installers guide. However, I fail to understand why you would want to do this, as locking out either HP or back-up heat is normally reserved for fossil fuel combinations. The COP of electric heat is 1; a heat pump will always be more than 1 as long as the ambient is above -17 degrees. Run a heat loss, then plot that loss on a balance point chart. Look up the capacity of your HP at 47 and 17 degrees and plot that on the chart. This gives you exactly how much heat you are producing as compared to the heat loss at given ambients. I believe you will find that adding ODTs on the strip heaters to stage them based on your BP chart findings will make your client more comfortable and happier with their energy consumption.

Heat Loss

@ February 1, 2014 5:42 PM in Temperature stuck at 64 degrees

Follow icesailor's lead. No heat loss equals no way you know what is needed, so don't spend a dime without one.

64 Degrees

@ January 31, 2014 2:23 PM in Temperature stuck at 64 degrees

Does the upstairs unit have an independent thermostat? If not, you won't have heat if the downstairs portion satisfies the heat demand. Did anyone run a load calculation before choosing the size of the heater? If not, then no one properly knows the amount of heat needed to replace the heat you are losing to the outside of the structure.

Fan Off Time

@ January 31, 2014 2:11 PM in fan running too long

If your furnace is an older model, you possibly have a combination fan/limit control with adjustable fan on/off settings based on temperature inside the heat exchanger. If the off setting is set too low, the fan will obviously circulate until that temperature is reached. If this is the case, hold the round dial so it doesn't move and slide the off pin to 100 degrees.

A newer furnace with a circuit board will have the same logic; shutting off the fan at a certain point, usually based on a certain number of seconds after the burner shuts down. Look for your control on the wiring diagram to see if it is manually adjustable. A temperature probe placed inside the heat exchanger helps to determine the actual shut down temperature versus the temperature selected on the control.

An even newer furnace will have an integrated circuit board in which the fan off setting is manipulated by dip switches. However, the maximum is usually not more than 120 seconds to avoid blowing air below body temperature. Integrated means beyond the dip switch selection there is no repair possible; the IFC would have to be changed. Again, do the temperature test to ensure you're not part changing for an incorrect reason.

York 3-flash

@ January 30, 2014 7:06 PM in Been away awhile....Anyway, Furnace Help Needed

The integrated furnace control compares the values sent to it by the pressure switch and the pressure sensor. If these values are not the same, the IFC will lock out with a 3-flash. You will need a manometer and a DC volt meter to see if these two components are within the tolerances listed in the IOM. Some causes could be poor connections, faulty wiring, or a failed pressure transducer. It obviously isn't the pressure switch if the issue remains after changing it. Check the PS wiring, the inducer wiring, the PS tubing for leaks or cracks. Also examine your vent system for restrictions (termination kit must match the IOM; 1/4"/ft. slope back toward the furnace; no sags or dips). Make sure the vent system TEL is within tolerances for your pipe size.

A good method for checking wiring is to use your ohm scale (NOT the idiot buzzer). Since the hot and neutral wires are the same gauge, they should register the same ohm value. If one is 3 ohms and the other is 1 ohm, you have a broken wire or loose connection at the molex plug. This logic can be used on all wiring.

Wow Follow-up

@ December 31, 2013 10:31 AM in manometer

Figuring out design methods is a non-issue, so don't worry about that. This is all about pressure, and the ability of the blower you have to deliver that pressure against the resistances (pressure drops) in the system. This brings out another fallacy of direct-reading a calculator. The calculator gives you a friction rate, which is the total pressure from blower inlet to outlet. You can't confuse this with a pressure drop, which can occur at any point in the system, and your duct calculator doesn't know what pressure drops you have. For example: if you have a blower that delivers 800 CFM at .55 IWC and you have a 100' duct sized accordingly, you're going to get that 800 CFM. If you add a coil with a pressure drop of .25 IWC, your FR has gone down to .30 IWC. With that same duct, how could you possibly get 800 CFM? Yet every day, you have people telling you this doesn't happen, because they've "been doing this for 25-years and never had a problem." OK, I believe you, and I'll bet you put in a Taco 007 in every two-storey house because "it should work."


@ December 31, 2013 9:50 AM in manometer

It's certainly not you, so don't beat up yourself. It's an industry problem brought on by those lacking understanding of air principles teaching us their lack of understanding. In the 8 x12 duct situation, there are ONLY two situations in which that duct will produce that CFM at that pressure: (1) the duct is exactly the equivalent of 100 feet, and; you have a blower that will PRODUCE .10 IWC of pressure.

It's the same scenario with that stupid 400 CFM/ton thing. They only tell you that to keep you out of trouble. Reading a duct calculator directly and 400 CFM/ton may work; it's just not the right thing to do. High static pressures nationally prove that. Wonder how 400 CFM came about? If you look at studies based upon years of research, and you look at all of the CFM per ton amounts that those jobs should have had and average them, you come up with 400. Does a customer deserve average? They are certainly getting it because over half of the duct systems nationally are underperforming.

Believe me, doing it the right way doesn't take that much more time than using some ridiculous formula someone invented based on averages or rules of thumb. And you give customers the comfort and economy they want, need, and flat out deserve.


@ December 30, 2013 6:57 PM in manometer

Paul's original comments were related to an existing system, or at least I assumed as much, since he mentioned troubleshooting. In this case, the procedure is to establish the ESP (external static pressure) from the blower inlet to outlet. This encompasses everything in between; ducts, fittings, registers, grilles, filter, coil, dampers, etc. You then break down the total as to how much pressure is in the SA and the RA so you can see where the problem lies. It's usually easier to relieve pressure on the return side than the supply since the ducts are generally more exposed. Then you determine the pressure drops of the coil and filter and subtract them from the ESP to give you the duct pressure that the blower is trying to overcome. I gave Paul some early warning signals due to the manufacturers rating their blowers at .50 IWC, thinking that amount should be enough pressure for a good duct system and external accessories. However, the national average ESP is a whopping .82! At .90 IWC, the blower is cooked! This means the average duct system is performing at about 57% of its capacity, so you can be a real hero fixing comfort problems with a small effort at overcoming that "I design my ducts at point one" crap.

Duct Pressure

@ December 30, 2013 9:32 AM in manometer

There is an easy way to do this, yet the discussion is too involved for the space we have on this platform. Contact me anytime. In short, you determine your system total pressure by readings directly at the blower inlet and outlet. Then you determine the pressure drops across all external components; evaporator coil, filter, dampers, etc. subtracting the pressure drops from the total pressure leaves you with what the blower "sees" in the duct system. The "early warning system" is if either your supply pressure or return pressure are at .20 IWC or above, or your duct system pressure is at .30 IWC or above.

Interestingly enough, it is these very principles that will show you that someone who looks at a duct calculator and tells you that an 8x12 duct at .10 IWC moves 480 CFM doesn't have a clue about air flow.

Flash Code

@ December 24, 2013 12:20 PM in aire-flo gas furnace not reaching target temp, i have flash code

You have presented two distinct issues: open limit and roll-out switch. Regarding the limit, if the filter was formerly plugged and the limit continues to open, the blower assembly or the indoor coil (if you have air conditioning) may be full of dirt, or you could have a duct system issue. The roll-out has a very specific job to do, as it's name suggests, which could be related to gas pressure or lack of combustion air.
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