I have extended the concept of putting active rooms on the south to identifying and grouping key functions, excluding sleeping, where the bulk of these activities can take place in an Active Area that can be kept comfortable more efficiently. The temperature in the rest of the house is allowed to fluctuate with little discomfort.
Say it would cost you $X to heat the whole house to 64 degrees. I’d rather pay a little less and have it 4 degrees warmer (68 degrees) in 1/3 of the house where I’m sitting and working, or reading, or whatever, and let the rest of the house be 60 degrees where I’m not!
I have been recommending this to my Home Energy Advisors customers for years, especially in big old houses. The idea came from my experience as a kid growing up in a farm house where there was no heat upstairs in the bedrooms and little heat away from the kitchen. We all gravitated to the kitchen area; it seemed natural, not like we were sacrificing.
Note: This concept is not as important if you build a smaller home, especially if it is a single floor, with thermal slab on grade. But in a bigger house, and I do regard 2100 SF as being big, but sort of necessary for our family of four.
An advantage of building new is you are able to cluster more activities in your Active Area, and by design you can place this area on the south side where it benefits from solar heat and light.
In our situation, we find that cooking, eating, reading, computer access, TV, homework, laundry, games and most hobby activities can all take place in this Active Area. That is probably over 85% of our daily activities take place in these 700 square feet, which is about 33% of the overall space. It is not exactly the 80/20 rule, but it is close.
One of our highest priorities is to keep the Active Area “comfortable.” For us this means keeping the temperature between 68 and 75 degrees year round – without using any fossil fuel. The rest of the house can and will experience larger temperature swings, but this is OK with us.
So, first we maximize our conservation of heat in the space by insulating the ceiling (kids bedrooms upstairs) and back wall (our bedroom suite). This additional insulation slows heat movement to those areas, plus it helps cut down sound transmission as well.
Next we give this area priority heating in three ways:
First, passive solar: We have the bulk of our south facing windows in this area – a total of 104 square feet of glazing for about 700 square feet of floor space. This is more glazing than is typically recommended for passive solar heating; however, the rest of the house is under glazed for passive heating and when the Active Area overheats, we can move heat to those other areas.
Part of the passive approach is that the whole first floor is a 3 ½” thick concrete slab. This slab is just for thermal mass. When the sun shines on the floor, a lot of heat is captured in this mass and will release later after the sun goes down.
Second, supplemental heat: If there wasn’t sufficient sun in a given day, we can run hot water through PEX tubing in the floor in the evening from the active solar thermal storage. It is important to run this for just a few hours, so solar collection will not be impaired the next day by having the floor already heated. If we need a little heat in the morning, we can run the “air source heat pump.” This warms the air without heating the slab. This unit was primarily purchased to provide AC on the hottest summer days, but it also provides energy efficient heat with outdoor temperatures down to 20 degrees. Either circulating a little hot water or running the heat pump (installed by Ed Bishop of Enhanced Living) can take the chill off without a lot of energy or effort.
Third, the wood stove: If we need more heat or if it is below 20 degrees outside, we have a small (maximum output: 42,000 BTU/Hr) Jotul woodstove. When the sun doesn’t shine for more than a day, we can use this carbon neutral fuel to heat the Active Area and the whole house, if necessary.
The heating load for our whole house is less than 10,000 BTU/Hr. “Heating load” is defined as the BTUs/Hr required to heat a house during just about the coldest hour of winter, typically 3 AM on January 21st! It was hard to find a stove that could burn all night on its low setting and not deliver any more BTUs. We chose the Jotul F 3 CB, an efficient, clean burning, cast iron wood stove – purchased from Woodburning Warehouse in Watervliet. Because the house retains the heat so well, just firing the stove for 3 or 4 hours will provide enough heat for a day.
There will be days when the Active Area overheats, whether by the sun or wood stove (intentionally or accidentally). When that happens we can cool the Active Area to a comfortable temperature without “wasting the heat” (opening a window), by sending the excess heat to other areas of the house – see Heat Management System in a future blog.
Most of the Year
It is important to keep in mind that most of the year, the whole house will be quite comfortable and activities can occur wherever desired. Maybe as many as 300 days of the year!
Only on a few summer days will AC be used, and typically just in the active area. On most winter days the Active Area will be heated solely by solar energy and the other rooms will be just a bit cooler. On those days we will keep the heat in the Active Area and gravitate there; this is part of what I believe is a necessary mind set change – adjusting what we do and where we do it, to live within our energy resources – rather than just flipping a switch to burn fossil fuel and pollute the air.
Due to the insulation levels and air tightness of the house, our heating season will only be about four months. The sun will provide the bulk of the needed heat to the whole house. Still to make solar ends meet we will need to add supplemental heat. But not much! Over the winter I expect to burn just 1/3 of a full cord (a face cord – 16”x4’x8’) of hardwood (this is hobby burning and quite enjoyable exercise) and use less than 1500 kWh for the air source heat pump and active solar circulators.
As I accumulate temperature and energy data, I will share it. I will be able to say what the average temperatures were by space and what actual fuel quantities and costs were, as well as the number of days we needed to light a fire – thus, I will be able to quantify comfort and cost.
* I coined the name Active Area for want of a better one. If you have a better name, please let me know.
Dan Gibson is Reporter and Chief Coordinator of Our Energy Independence Community and Chief Energy Auditor and Solar Designer for www.HomeEnergyAdvisors.com. He previously spent 5 years performing home energy audits in NYSERDA’s Home Performance program. He is also currently “finishing” their 100% Solar Home – no, three years in the making and it's not finished yet. He can be reached at DanG@OEIC.us or at (518) 899-2400.