It has been a while since we have posted and a lot has happened at 1209 Touro. We have the majority of our mechanical, electrical and plumbing systems roughed in. Each of these has carried with it a lot of decision making, and I’m not talking about whether your faucets are brushed nickel or polished chrome!
We will be sharing our decision process in a series over the next couple weeks, since showing pictures of ductwork, electrical wiring and plumbing pipes is neither exciting nor informative. And we are starting with the most difficult (and expensive) of all – the HVAC system.
A house’s mechanical system includes heating, air conditioning and general venting. We decided to install a central air system. There are other options to this type of system, but the industry standard for residences is currently central air.
The mechanical system selection depends on three things: the total tonnage requirement of the home, the functionality of the system (multi-system vs. single system vs. multi-zone), and the SEER of the unit itself.
To determine the tonnage requirement, we had an energy consultant do a J-load calculation. From the Internet – A Manual ‘J’ was developed by Air Conditioning Contractor’s Association (ACCA) and is a detailed calculation of how much heat is gained or lost by your home under a specific set of conditions. It includes such things as the size of each room, the size of the windows, type of windows, size of door and their type, insulation and magnetic orientation of the home. Ideally the subcontractor providing your insulation will perform the J-load, at a minimal cost.
In order for this calculation to be performed, we had to make a decision about insulation in the walls and at the roofline. Our next post will cover what we have decided and hopefully include some pictures of the install, since that is our next priority in keeping the schedule in tact. Our J load gave us our tonnage requirements in the range of 3 ½ tons to 4 tons. We opted for a 3 ½ ton system due to the issues that can arise with an oversized system and because we don’t keep our house extremely cold. (Human comfort zone is around 73 degrees).
We chose to do a multi-zone system rather than doing separate single systems (multi-system) for the upstairs and downstairs. Here is some information on how a multi-zone system works.
For the SEER of the unit, we went with a rating of 14. Our choices were 13, 14 or 15- with the higher number being the most efficient. There was about a $900 jump on the cost of the system for each SEER unit increase.
Two things influenced this decision. The first was an article I came across that suggested a 14 SEER unit will soon be the code minimum – that eliminated 13. And the second was our conversation with the HVAC subcontractor – why buy the most fuel efficient car if you are only driving it a couple miles a day? We aren’t going to set our thermostat at 60 degrees and therefore may never really see the life cycle cost benefit of the more expensive unit.
Another thing that helped us decide against the 13 minimum is the $300 tax credit available for installing a 14 SEER unit. Here is some information on that. (We will also be taking advantage of the $500 tax credit for insulation).
Another step in the HVAC decision making is where and how to route the ducts. In a house that historically did not have air conditioning and no longer has an attic, this was quite a puzzle! Here is a picture of the unit, located in the leftover attic space above the back bedrooms.