High Performance HVAC Air Conditioning & Heating: Sun Porch and What Type of HVAC System Needed?
The Sun Porch or Florida Room: What Type of HVAC System Needed
15) We added a 300 sq.ft. of living space to our home as a sun porch. How do we effectively, efficiently heat/cool this space? We’ve been pitched several options. 1) Use existing with a manual duct damper to the new sun porch. 2) same as above but use a zoned approach w/auto dampers for main house 1st floor and sun porch plus separate thermostats. 3) HVAC with new units for sun porch (e.g., radiate, forced air, etc)
Sun porch is a 15×20 fully enclosed insulated space with 6 ft. casement windows on three sides. The forth side is the main house wall. Main house is 2 story, 1600 sq ft. per floor, gas heated with 2 Trane furnaces and cooled with 2 Trane central air units. The Trane equipment is new being installed in 2007.
This is Richard from High Performance HVAC responding to your question your sun porch and the type of HVAC equipment you need to keep it comfortable. The first thing I thought for your dilemma was a mini-split heat pump as I’ve seen many of these systems used successfully on sun porches. However, I see you reside in Illinois and I don’t believe heat pumps can take the cold winters there and provide effective heating for constant temperatures less than 38 degrees F. A mini-split heat pump with back-up heat strips would work. Electric heat is expensive but the installation cost for the mini-split is cheaper than a full sized HVAC unit (minimum sizes with these units are 1.5 tons which is too much for what you need) plus you don’t need duct work with the mini-split. You could get a straight AC mini-split with heat strips in the air handler portion for back-up heat on really cold days and the gas fired radiant heat. None of this would require duct work which is good because their are no future problems with replacing or repairing the duct work.
I’m not a big fan of the automated duct dampers in residential systems. I’ve seen too many problems and heard too many complaints about them. Some contractors swear by them but I will not recommend something that i don’t have confidence in and I don’t have confidence in these systems. The other problem which arises when thinking of using this type of system (automated damper system with two thermostats) is the size of the unit. Is the other parts of the house going to suffer or is the unit going run too hot when only one zone is calling. It will probably have a bypass damper so you only get the required amount of BTU airflow to the sun porch but where does the bypass bypass to? Back to the furnace where it will cause the furnace to short cycle (which is the common method of doing it in a system like this)? Does the furnace have staging to prevent short cycling and if so does the contractor have the talent necessary to hook up the controls properly to make work right?
Another option for heating and cooling the sun porch is to install a PTAC unit. PTAC units are through the wall heating and cooling units that most people will recognize from hotel rooms and is pictured above. PTAC is an acronym of portable terminal air conditioner.