Here is a thermal photo taken behind the front panel of our heat recovery ventilator. Sadly, the thermal camera do not save the pseudo-color scale with the image, but the image is still simple to interpreter. The cooler colors refer to colder areas in the image, warmer colors to warmer spots. The metal surfaces reflect infrared similar to visible light, but I think this photo represents fairly well what is going on inside the ventilator. On the right side is the channel that pulls waste air from the rooms by the blower in the bottom part of the image. The warm waste air is blown through the heat exchanger that can be seen in the middle of the image (the tilted square object). After the heat exchanger, a little bit cooled waste air goes out of the house, the exit channel is in the middle-upper part of the image. The dark blue portion of the image is the channel where the cold outside air comes in. As you can see, it is heated up pretty much as it goes through the heat exchanger and arrives in the space lower-left corner. There the intake blower blows the air upward towards the rooms. The red/white glowing electrical heater gives extra heat to the fresh air if necessary. There are a couple of filters inside the ventilator that keep the motors and channels clean and prevent outside particles entering the house. This system is ecological and economical way to keep home warm and healthy, especially during winter. Instead of relying only on the natural buoyancy based ventilation, the active ventilation keeps the moisture from building up into the structures of the house, together with the moisture buffering wood inside our log house that damps moisture spikes. This is especially important while using shower, taking sauna, or cooking a lot, because our house does not have the best possible vapor barriers, and the water condensing cold lurks everywhere.

Thermal photo outside of our house. The hot spot on the roof is the ventilation channel where the waste air comes out. The heat recovering system is not 100% efficient.

In closer inspection I noticed the hot spot in the base of the waste air pipe. If it is a leakage in the channel itself, it could cause serious problems. Warm and moist room air combined with the cold structures of the roof will likely cause condensation that could eventually lead to microbe growth. However, I found that the heat came from the warm chimney used when the photo was taken. The heat distributes by convection in the attic, and this spot was one of the snow-free places were the heat radiated out towards the sky. So, although we have mechanical ventilation inside the house, it is good to realize that there is always buoyancy based ventilation in every open space, even in the attic. It helps to conduct moisture out under the roof.

This is the source of the heat. This chimney has three flues, and only one of them was in use when the photo was taken.

Here is the chimney seen in the attic. No other major sources of heat escaping the rooms were seen here. Notice that especially under the diagonal wooden beams the blown insulator can become compacted during the years due to the gravity, and open channels (cold bridges) could form. Non of them are seen here, because I have manually refluffed the blown insulator in all the risk spots.

Our cozy wood stove in use 🙂

Another photo from the attic. This can be a problem. These are stairs to one of our bedrooms, which can be laid down from the ceiling. Although the door on the ceiling is closed, a lot of heat is leaking to the attic. In the bedroom, cold flowing air can be easily felt with a bare hand. Well, due to the flow of the air inwards (thanks to our ventilator), this weak rim around the door do not maybe cause problems. At least it is not in the kitchen or shower, where most of the moisture is produced. That is why it is important to have small low pressure inside the house, so that the moist room air do not enter into the structures and condensate there.

Here is an outside thermal photo of our technical room. There are a lot of heat sources in the relatively small space, such as the water heater. Still, this thermal leakage does not look good. However, if I do not find any problems with moisture, I will not to try fix it. It would be a hell of a work to move the water heater. At least the house is pretty old already, and hasn’t rotten yet 🙂

These leaking door seals are easy to fix on the other hand. I will do it later.

During the independency day of Finland we grilled some sausages outside.

And here is the fire place after grilling. Notice also how the trail in the snow and the great and wise rowan conduct and emit geothermal heat. Snow is a good heat insulator.

A hot tit observed at the bird feeder I made 🙂

Here is a thermal photo I took from my workshop. Clearly, there is warmer microclimate in the porch.

In my workshop I built a buoyancy based ventilation channel for the waste air. When I’m not in the workshop, I keep it at about 8-10 degrees of Celsius. Still, the natural convection works pretty well, as it can be seen that the waste air channel on the outside wall glows nicely. I cannot see any leakages in the attic on the other hand. I used urethane foam to seal a few bad leakages in the workshop ceiling, otherwise the warm and possibly moist waste air could go into the structures of the roof. Now the only major escape route is the ventilation hole seen here.

So, about the over pressure modification I made to our heat recovery ventilator. There is an over-pressure switch for pumping a lot of extra air fast into the house, made to aid starting fireplaces. However, we haven’t used it much, we can start the fires even without the over pressure. Furthermore, even in a few minutes the extra blow cools the rooms pretty much. Thus, the switch has been unnecessary. On the other hand, we cannot use the ventilator in normal speed settings either when burning wood. Even in the lowest speed the ventilator causes small low pressure in the house, to keep the moist room air away from the structures. The intake and outward blowers blow with the same wattages no matter what the speed setting is, but the ventilator channels are adjusted to choke the flow of the fresh air a little causing low pressure. The ventilator should not compete with the fireplaces, because in worst case the ventilator could pull carbon monoxide inside the rooms and cause even death. However, because the fire need to take combustion air somewhere, it pulls it uncontrollably through all possible ventilation channels, and the heat recover and the electrical heater inside the ventilator do not work if the device is turned off. Thus, it is ironic that while using our fireplaces we might feel chilly due to the cold replacement air that distributes all around the house! After all the smoldering has stopped, flue plate is closed, and the ventilator is turned on, the heat left in the used fireplace distributes around the house and is captured by the heat recover. Before that, a lot of energy is lost. In the lowest normal speed setting both blowers get 100V from the transformer. However, there were even lower options also, 60V and 80V outputs. After considering and experimenting a little, I modified the over-pressure switch so that the intake blower takes 80V and outward blower 60V. The 60V was enough for the outward blower to start, but the intake blower was clearly faster. According to measured currents, I calculated that the intake blower took about 1,85 times more power than the outward blower. Now, when the over-pressure switch is turned on, air is only nominally circulated through the heat recover without disturbing the combustion (it is supported a little). Now we don’t feel cold anymore while using the fireplaces, since the liberated heat can be captured and distributed during the whole combustion process. The internal heater of the ventilator can also be kept on. I tested a possible dangerous fault state by totally disconnecting the intake blower. Although the outward blower fed with the 60V was running, two days earlier heated stove flue managed to pull the room air. So, if the intake pump, that makes the over pressure, breaks for some reason, this should not cause problems with carbon monoxide. Especially, in smoldering phase the used flue is already super hot and should strongly pull the air. While starting the fireplace, it is closely monitored, and backward air flow should be observed quickly. And oh, when our wood oven is in its “full speed”, it sucks strong low pressure into the house, it can be felt in hand although the high pressure setting is on. So, if normal room air is pushed into the structures, the state lasts only a while.

Unfortunately, I did not take a comparative photo of the ventilation channels on the ceiling before the modification, but they were dark blue during the combustion due to the cold replacement air they fed inside. Now, with the new over-pressure setting, the intake channels supply warm air into the rooms. The hot glowing background is due to hot convention coming from an electrical radiator.

A little extra story. Once I took my water bottle and started to scout the surrounding forests. I think I walked about 7 km in the snowy forest, just wandered around. Then I found these marks on the snow, I think it was a lynx.

The creature took a long jump over this funny little canyon, and I continued to other direction. Back to home to enjoy the heat 🙂