Mechanical Ventilation - Better Air, Money Savings, Safety, And A More Comfortable Home

Anyone who has spent money on tightening up an existing home or spent extra for energy upgrades for a new home will be irritated by the concept of mechanical ventilation. Understandably it doesn't make sense to make a home more airtight then add a way for more outdoor air to come in, but having your home ventilate properly is critical. Why?

Indoor Air Quality- Indoor Air Quality or IAQ has become a buzzword in the HVAC industry. Sometimes buzzwords come about from marketing or misinformation but here there is a legitimate need, as homes are tightening up pollutants are trapped in the home. Older homes are ventilated naturally, but at the cost of comfort and efficiency. Indoor air starts as outdoor air and becomes "dirtier" from pollutants in the home, ventilation removes dirty air and dilutes the existing air.

Common sources.

Excess moisture. High humidity can lead to condensation which can lead to mold.

Chemicals. Paint thinners, cleaning products, insecticides such.

Building Products. Most newer products contain chemicals from their production like glues or formaldehydes.

Pets. Dirt dust and dander

Smoke. Candles smoking or even deep frying let off contaminates that hinder breathing.

Energy Savings- The issue is air is coming in whether you want it to or not, any home exhausts a certain amount of air through bath fans, kitchen exhaust hoods, water heaters, older furnaces or one pipe furnaces, stack effect from leaky can lights, hvac boots, attic hatches or clothes dryers. All the air that leaves will be replaced through cracks, outlet boxes, open doors, or far worse a back drafting water heater flue. Since that air is coming in our goal should be to control it. Mechanical ventilation allows us to bring it into the duct system where it will be conditioned and filtered before coming into the living area. Some types of equipment have heat exchangers that pull the heat out of air before it is exhausted.

Comfort. By controlling where the air come in we reduce drafts and cold spots.

Safety. We know how as our homes vent or exhaust air the air needs to be replaced, this is called negative pressure. The safety concern comes when a home has a fire place or b-vent water heater that begins back drafting from the negative pressure. If air is being introduced through the b-vent when the water heater fires the exhaust gases will spill from the draft diverter allowing co2 into the house. mechanical ventilation reduces this condition. Regardless of your situation you must have co2 detectors in your home.

Basic types of ventilation

Exhaust ventilation- Removes the contaminant at it's source, like a bath fan or kitchen exhaust hood. While this qualifies as mechanical ventilation it is hardly optimal. Exhaust only leads to unbalanced pressures, drafts and potentially unsafe backdrafting.

Supply Ventilation- Provides a means of introducing fresh air into the home to replace exhausted air and help with dilution of home contaminants. Traditionally a duct is ran from the cold air return of your HVAC system to the outside metered by a barometric damper or an electronic damper that opens and closes based on preset conditions. Of the two I prefer the electronic version. By bringing the air through the return we can condition and filter the air before it is introduced into the living area. Coupled with quality bath and kitchen exhaust fans this setup is effective and should be your minimum standard.

HRV/ERV- Stands for heat recovery ventilator and energy recovery ventilator. An HRV/ERV is a balanced exhaust system that runs the exhaust and intake air through a heat exchanger, pulling the heat out of our conditioned air before we send it outside. An ERV is the same setup that also pulls out humidity making it a great fit for hot humid areas. HRV's can be installed stand alone or tied into the duct system. Based on conditions set by your installer the unit will exhaust and replace the same volume of air with reduced heating/cooling load due to the heat exchanger. Another fantastic idea that I saw involves a remote mounted bath fan that pulls air from several bathrooms that ties into the ERV. Instead of sending that warm steamy air outside it is ran through the ERV.

Below is a generic diagram of a typical ERV.

Aaron@onhomecomfort.com
http://www.onhomecomfort.com

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