Our house has spray foam in walls and roof, so we have an enclosed building envelope. The good, our AC bill is lower in the summer. The bad — our HVAC system was not properly installed... and the correct type of unit was not installed.
Our builder had a 3 ton unit installed. No heat pump, single speed blower (it has multiple sppeeds but is set only for one), an outside make up air duct, filters at the registers and no damper on makeup said vent.
We were on a maintenance contract with an HVAC company, when they inspected last fall, there was mold throughout the system.... they bid $4500 to do cleaning and add UV light. So... we called a few HVAC companies.
What we learned for spray foamed:
- HVAC needs a fresh air vent with an electronic damper control. We just had an electric damper installed April 2021... the dust in the house is 90% less.
- HVAC should have a 4” filter at the unit (no need for filters at the registers). If dust isa major concern, consider looking into an electro static precipitator at the unit too
- HVAC Ducts
—should be connected with Wyes. Ours initially had triangle boxes. The wyes have less resistance and therefore allow more air to flow through and reduce the static pressure so the fan does not have to work as hard.
— Look at where the ducts are routed... we have lots of space in attic, but it’s unusable because of wires and ducting
— consider solid ducts rather than coiled — much easier to clean and less static pressure
— HVAC main unit should be a variable speed unit.
- Heat pump would be good as well
- Humidity control is a challenge... the dehumidifier will be $3500 if we decide to have it installed... we are adding a vent fan in the master bath area to remove steam from shower. Major sources of humidity are showers and cooking in our house.
EcoBee thermostat— great control, includes humidity monitor, can over cool to reduce humidity
HVAC — after having the unit cleaned, the HVAC company installed a UV light in the coils area.
— consider adding surge protection for HVAC, especially if using a higher SEER unit
— after snowmageddon 2021, I would consider installing a propane furnace
Building envelope -
- with spray foam, the building envelope is sealed, so there is minimal air infiltration... makes for better efficiency if there are no leaks
- we had three HVAC companies out to look at our system. Only one (Larco in Millsap) took the time to walk across the attic to the fireplace.... found air gaps around the chimney, which is another source of humid air to enter.
Our $2200 HVAC temporary solution :
Replaced triangle duct boxes with wyes
Built new plenums (old was moldy)
Installed UV light
Cleaned coils and blower fan
Sealed around fireplace
Installed 4” media filter
added electronic damper
