Performance so far: easy to heat; no air quality problems

It's January 2004, and I've been sleeping in the house for a few months. I still use my trailer for cooking.

My main concerns as winter set in were:

1. Would the slab be a cold, dismal floor?
2. Would air quality be bad?

It turns out I had no reason to worry.

Update April 2005: All of the following is still true. Basically, the house is very comfortable with one radiator and one "room" air conditioner that are both half the recommended size. Heat is surprisingly uniform, especially considering that the wood stove and radiator are downstairs and there's no ductwork. The assessor claims I have no central heating!

Cool, not cold floor

The slab is cool, not cold. Near the woodstove it's warm, even if I haven't had a fire for days. I often go barefoot. Guests wander about in their socks. The only time my feet get cold is when I sit for a long time with my bare feet on the slab.

The slab is most comfortable when I use the woodstove. When I rely on the propane heater for several days, the slab seems to lose some warmth, although the air temperature stays the same.

No big temperature swings

The mass in the slab clearly slows down temperature swings. My little woodstove conks out about 2 a.m., but the living room is still warm in the morning with no help from the propane radiator.

In the summer, the slab helped the house stay 5-10 degrees F cooler than the outside temperatures. Visitors thought I had air conditioning. Early in the summer, the house was cooler even with the windows open. Later on, I closed the windows during the day and opened them at night to keep the slab cool. It probably helped that the slab hadn't been heated during the winter.

Easy to heat

Besides the sun, I have two heat sources: a propane radiator and a small, efficient woodstove. Both are on the first floor and either could heat the house alone, though the propane radiator reaches the second floor better.

In December, I occasionally relied on just two 1500-watt space heaters, one on each floor. When nights were in the 20s F and days were in the 30s, the two space heaters kept the indoor temperature in the low 60s.

Woodstove: even heat

The woodstove is a small iron stove (Waterford Leprechaun) lined with firebrick. It sits on the slab and has a slate-tiled wall behind it.

The stove is slow to have an effect, but its heat seems to distribute itself magically through the house. The second floor doesn't get warmer than the first, even though the woodstove is next to the open stairwell and the steel chimney is exposed upstairs. I occasionally use a 1500-watt electric radiator upstairs when I'm relying on the woodstove.

Propane heater: stratification

The propane heater is a sealed combustion "wall furnace" that mounts on an outside wall on the first floor. It has no fan. I thought it would provide radiant heat, but it seems to work most by heating the air that rises past the heating element. The result is warm air at the ceiling and a slight difference between first and second floor temperatures.

The radiator is sized to heat only the first floor, but it easily warms both floors. I clearly don't need a second radiator upstairs.

I chose the propane radiator partly because I thought it would be silent, since it has no fan. I was unhappy to discover that I can hear the pilot light burning, even when I'm upstairs. I have absurdly sensitive ears, but that one pilot light does seem to make an unusual amount of noise.

I use both

I prefer the woodstove's radiant heat. It warms the slab as well as the air and distributes itself more evenly. So I use the stove when I'm home long enough to get a good fire burning and charge up the slab.

I usually figure if I have two hours to keep a hot fire going, it's worth firing up the stove. When I'm in town for long periods, the propane radiator kicks in.

Good air

I've been using an air quality monitor (senses VOCs) and my own sensitive nose to look for air quality problems. So far, the only problem occurred when I brought a new comforter cover into the bedroom, which sent the air monitor into a tizzy. I washed the cover and the problem went away.

Otherwise, the monitor registers little or nothing, which confirms my sense that there's no significant formaldehyde offgassing from the SIPs or manufactured I-beams. They've been in place for almost a year now.

Ditched the HRV

I originally planned to install a heat recovery ventilator, but now I doubt that will be necessary. When I want ventilation, I crack open some windows and turn on the bath fan.

I'm reasonably confident that the kitchen fan can handle the moisture that will be introduced once I have a real kitchen. So far, the humidity hangs around 38%.

It's possible that future owners of the house would want an HRV so ventilation is automatic. My current system requires some involvement and a commitment to avoid materials that offgas nasty stuff.

Endless hot water

I have a Takagi T-KD20 on-demand propane heater on the first floor to provide hot water for both the kitchen and bath. So far, it's worked well, though it takes a few seconds of flow before the water warms.