Heating and Cooling Questions

My upper floor does not receive enough heat. Can I adjust this?

Try balancing the duct distribution system. To do this, look at your main supply duct where it leaves the heating unit. Follow it until you see the supply branch round ducts leading off to serve individual rooms. There will be a handle to the balancing damper on each round duct. Close the damper by turning the handle up or down, but not parallel to the duct. This will restrict airflow to rooms that get too much warm air, particularly smaller rooms such as bathrooms. Some rooms on the first floor may also be too warm. Then make sure all dampers to ducts serving the second floor are in the full open position, with the handles more in line with the duct.

We have a new house, but two of our radiators won't heat up properly. What's the problem?

It may be the vent. To test, turn your thermostat all the way down, wait about five minutes, and then unscrew (very carefully) the vent from the side of the radiator. Turn the thermostat back up and wait for steam to be made. If the radiator now heats up, you just need a new vent. A WORD OF CAUTION: DO NOT OPERATE YOUR SYSTEM WITH THE VENT REMOVED. After this test is done, reinstall the vent until you get a new one.

I am going to get a new heating and cooling system. Which one is the best?

Brands are important—and the most well-known names are all good—but the installing contractor plays a more important role. You might have the best equipment but if poorly installed, it will not work as well as it should and will be less efficient. Check the contractor. Get references.

A good contractor will more than likely install good equipment properly. The second part of this

equation is proper sizing of equipment. Ask to see the contractor's heat loss and heat gain calculations for your home.

When my furnace kicks on, I hear all kinds of clicks and clacks and booms in the ducts. What's the problem?

Your noisy ducts could be caused by a number of things. One of the most common problems is undersized ductwork, which causes the ducts on the supply side to expand as they pressurize.

This in turn creates a small vacuum on the return side. In both cases, the ducts will expand and contract. When the blower comes on, the tin ducts begin making a banging sound. The other ticking noises could be the expansion and contraction between the hangers and the ductwork itself. Try isolating the ductwork from the hangers with some kind of rubber cushions. When the plenum causes banging noises, it normally means the return air part of your heating system is starving for air. Every warm air furnace manufacturer will give you a temperature rise number they expect to see from their unit. Check your unit by taking a temperature reading of the return air and supply air. The findings should match the manufacturer's requirements. If the temperature is too high, you do not have enough return air. This condition will shorten the life of the furnace.

It seems all homes have rooms with comfort problems! How come?

Any individual room that has more than two exposed walls deserves special attention. For instance, a family room over a cold crawl space with two outside walls, a garage wall, and an attic above has five exposed walls. Without effective blending and zoning practices, you cannot expect that room to be always the same temperature as the protected area around the thermostat.

Will a programmable thermostat make my house comfortable?

Not really. A programmable thermostat allows you to have more efficient settings, but this thermostat alone cannot make your rooms more comfortable. Only proper air balancing and zoning can do that.

Should I put a duct booster or register fan in the supply vent in my problem areas?

Supplementary devices like fans are available, but there is no substitute for good zoning practices.

The boosters usually only help when the system is running. If the system is not cycling properly or it was not balanced properly, these features will have only varying degrees of success.

How do I bleed my radiators?

It's a little like bleeding brakes. You turn the heat on, let the water start pumping, and then open the bleed cock very slowly to let the air out. Bleed cocks that do this automatically can be installed. The baseboard type of radiators may or may not have bleeders on them. The options here include a bleeder on the return side or a purge valve in the boiler area. In this case, connect

a garden hose to the purge valve. It is very important to keep air out of the system, which is detrimental to the boiler.

I want to put radiant heat in my kitchen when I install a new ceramic tile floor. What is the advantage of putting the radiant heat pipes under the subfloor between the joists versus in the mortar under the tile?

When you install radiant heat piping in mortar as opposed to under the floor, you get more evenly distributed heat, with fewer overly warm or cool spots. On the other hand, there is something to be said for going with the method that is easiest and thus less expensive to install. The floor temperature should not exceed 85 F, as anything over that will feel too warm on the feet. Also, remember not to put radiant heat under cabinets that will have food in them because the warmth is not good for stored food such as potatoes and onions.

Are there guidelines for deciding how big ducts should be for air conditioning units?

Yes, there are established industry standards and engineering guidelines for sizing air conditioning ducts. The most widely recognized authority for residential duct design in the United States is the Air Conditioning Contractors of America (ACCA).

1. Primary Industry Standards 

ACCA Manual D: This is the "gold standard" for residential duct sizing. It provides a systematic procedure to match duct resistance to the performance of the air handler's blower.

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ACCA Manual J: Before sizing ducts, a Manual J calculation is performed to determine the exact heating and cooling load (BTUs) for each room.

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ASHRAE Standards: The American Society of Heating, Refrigerating and Air-Conditioning Engineers provides broader standards for air velocity, pressure loss, and energy efficiency.

2. Core Sizing Principles Professional designers use several key metrics to decide on duct dimensions: 

Airflow (CFM): A standard rule of thumb is 400 CFM per ton of air conditioning. Each room's CFM requirement is determined by its specific cooling load.

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Friction Rate: The industry baseline for rigid metal ducts is typically 0.1 inches of water column (w.c.) per 100 feet. If using flexible duct, designers often use a more conservative rate of 0.08" w.c. or upsize the duct by 1–2 inches to account for higher internal resistance.

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Air Velocity: To minimize noise, residential supply ducts are usually designed for 600–900 feet per minute (FPM), while return ducts target 500–700 FPM.

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Total Effective Length (TEL): This calculates the resistance of the entire run, including the physical length of the duct plus "equivalent lengths" for every elbow, tee, and fitting.

3. Common Residential Duct Sizes While exact sizing depends on calculations, common sizes found in homes include: 

Small (4–6"): Used for low-airflow spaces like bathrooms or closets.

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Medium (8–10"): Typical for standard bedrooms or home offices.

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Large (12"+): Required for large living areas or main trunk lines.

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Rectangular Ducts: Often used in tight spaces (e.g., 8x16", 10x20") because they can fit between wall studs or floor joists more easily than round ducts.

4. Consequences of Improper Sizing 

Too Small: Leads to excessive noise ("whooshing"), increased energy bills, and equipment failure, such as frozen evaporator coils.

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Too Large: Results in low air velocity, which prevents air from mixing well in the room, leading to "hot spots" or stratification.

Source: https://dticorp.com/heating-and-cooling-questions/