7 reasons that make home temperatures uneven (continued)
In the first part of this analysis we discussed how home temperatures fluctuate, and what is the nature and mechanics. Read through, ask additional questions (in the comment section below), and you could fix this comfort issue without getting a contractor involved. Here are 7 reasons that make home temperatures uneven:
4. Ductwork acts as a stack pipe.
As mentioned above, when the fan shuts off, the supply branches and grilles in different levels act as a stack pipe. It is similar to a chimney effect. The vertical stack, called trunk, allows warmer air to raise to the top, creating negative pressure on the bottom of the duct, which in turn “sucks” air from everywhere it can, including crawl spaces, laundry and waste rooms, garage and such. All pollutants being sucked as well. When the fan starts, the air pushed the contaminants into rooms. But this is besides the story, this topic is about uneven home temperatures, not air contamination. Some offer to use a magnetic cover to block grilles and vents (assuming they are metal) or anything suitable to prevent air leakage. Not a good solution for a home with multiple floors. Instead a homeowner might get an estimate for a ductless mini split system. Ductless means no ducts, and no related problems.
5. Thermostat located in one of the rooms, or hallway
When the main thermostat located in one of the rooms, or hallway, it does not sense temperature in other rooms, will over- or under-work the heating and cooling system, and will never achieve desired temperature in all rooms. It will be too cold or too hot. Only a zoning damper system can resolve this problem. If installed, each room becomes a “zone” controlled by an individual thermostat. This way the temperature can be controlled more accurate. Ductless mini split systems does exactly this – it has a thermostat (or a remote control) in every room, and commands a dedicated unit in that room, which in turn allows for precise temperature control. If a home is heated and cooled by one main central system, with one main thermostat, it will never be comfortable, as temperature fluctuations can be severe.
6. Varying heat load in a room
Appliances like large flat-screen TV and computers can affect heat load. Special purpose rooms (gym, pool, kitchen) vary heat load as well. With central blower and common distribution duct, the heated or cooled air distributes between rooms with no regard to load fluctuations, while these are important conditions. Rooms with more appliances, like kitchen, or living/family room will be overheating, while other will not. And this is only when those appliances are on! So it is impossible to adjust amount of air entering the room with regard to TV being on or off. After all this should be a comfort system, not something a homeowner be constantly adjusting. The same applies when you have a party. When more people gather in one room, the room becomes stuffy and hot, but you will not get additional air in that room as the ductwork is not designed for it. Keep adjusting the thermostat, or get a computer-controlled ductless mini split system, which automatically adopts to varying load.
7. Central system thermostat is “on-off” type.
Even if the display looks digital, like new touch-screen thermostats, it is still analog “on-off” type. What this means is: it tells the central heating and cooling system to start blowing if needed, or stop blowing if the temperature is satisfied. Sorry for being so technical here. Modern central HVAC systems are equipped with ECM motors, multi-speed compressors and programmable thermostats. These devices meant to control the system output, sort of varying capacity. Nevertheless these innovative devises still do not do the job. Here is a little example: if a central air-handler fan slowed down, the conditioned air does not reach rooms as it should, as the whole air distribution system gets misbalanced. The ductwork is designed with certain parameters: CFM (cubic feet per minute), SP (static pressure) and AV (air velocity), changing which undermines the whole engineering. You cannot help it, but an “on-off” system creates temperature fluctuations. Run the fan on all the time, but this is waste of energy!
Central HVAC system cannot achieve constant and even home temperatures in the house, unless the fan runs constantly, and wastes energy. A ductless mini split system eliminates these problems, and the need to run the fan constantly, therefore saves energy.
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