We recently received a thoughtful email from prospective clients who have been giving energy efficiency and Passive House design some serious consideration; their primary concerns with such a well insulated and tight home is with ventilation of moisture, cooking smells, and excess cooking heat in summer.
We particularly enjoy these types of questions, read on for the questions and answers.
[From the client]
“I hope this is not too premature. We have been looking at kitchen
appliances and plumbing fixtures. We are starting to figure out what
we want and don’t want and are narrowing our choices down. Some
technical questions have come up that depending on the answers could
direct us in different directions.”
Q. We prefer cooking with gas and know that gas produces moisture. How would this affect the air environment of a passive house?
A. Cooking with gas works just fine in a PH. The act of passing the fresh incoming air across the heat exchanger within our Heat Recovery Ventilation (HRV) system tends to reduce the relative humidity level in the home. There is a small pipe at the bottom of the HRV that delivers condensation water to a drain.
In some climates, this drying effect is actually a problem, and in those cases we would choose an Energy Recovery Ventilation (ERV) system instead of an HRV. ERV’s manage humidity in addition to performing the heat exchange function of an HRV. However, in the pacific northwest, the ambient humidity and the action of the HRV act together to keep the indoor relative humidity at a level that is recommended for humans. Because enough air to completely fill the house is brought into the home through the HRV every three hours or so, cooking with gas has little impact.
Q. Cooking with either gas or electric produces lots of heat as well. In a passive house how comfortable will the kitchen be in the summer?
A. In a regular house, when it comes to dealing with cooking heat during the summer months, you can open windows and doors as needed. That’s what you will do in a passive house as well. Additionally, you can turn the HRV up to the high setting, using a booster switch that will be installed in your kitchen. This will bring fresh air into the entire house as needed.
If it is too hot outside to gain some relief by opening windows or running the HRV, you will be no worse off than you would be in any house. But living in a PH reduces the effect of high outdoor temperatures during those hot afternoons. In the summer, you can open things up at night and close them up during the day. Because the home is super-insulated, chances are that your home will be cooler than the house next door is on a summer afternoon. There will be days when you are enjoying your indoor temps and you don’t want to cook indoors and warm things up. But in a PH, you will have a better chance of avoiding having this be the case.
Q. Today we were introduced to the idea of induction cooking stove tops as a way to reduce the problems of moisture and heat. Do you have any thoughts on this? We are both not drawn to that style of cooking, but thought maybe we should consider it.
A. Some of our Passive H owners selected the induction cooktops. They are pretty neat! If you are attracted to the low energy use, fast cooking times, and the fact that the surface of the cooktop does not really get hot, an induction cooktop may be for you.
Some of our PH owners cook with gas. They have reported no issues specific to this approach. So, don’t avoid gas cooking if that’s what your prefer.
Q. When we were at Albert Lee in Tacoma we discussed the concept of recirculating vent hoods like you showed us in the two houses we viewed with you. The salesman there gave us the low down on them and seem to be not as efficient at removing the heat, moisture, smells, grease as a regular vent hood that exhausts to the outside. We have concerns about this technology and would like to understand better how the heat exchanger is going to take care of the recirculated air from such a vent hood?
A. I think it’s generally true that a recirculating range hood will not be as effective as one that is vented to the outside of the home. But when you have an HRV in your home, this is not a problem. The range hood is there to collect heavy steam and the grease that is in the air right above the cooktop. The HRV deals with everything else – minor cooking smells, moderate increase in humidity, etc.
It’s important to remember that the HRV is is moving a lot of fresh air into the entire home, and that this approach works well. Here is an analogy: If you have a pool in the yard that is full of water that is never cleaned, you will be really picky about keeping impurities out of the water. But if the pool has a stream running into and out of it all the time, the flow of water from the stream will keep the water in the pool clean, even if impurities are introduced occasionally. I hope this analogy applies for you!
Q. Like wise we are still concerned about the amount of moisture released by showers and cooking and how this will be evacuated from the house.
A. We will install booster switches in the kitchen and the bathrooms that you can use to turn the ventilation system up to the high setting.
Current ventilation code requires fans that are rated to remove 50 cubic feet per minute be installed in bathrooms. In actual practice, most fans in bathrooms today don’t move the amount of air that they are rated for. But we turn on those fans and they do the job if they are not too crummy! The typical owner of a regular home never knows how much air is being moved by the exhaust fan.
When you buy a PH from The Artisans Group, after the home is completed, Randy and an experienced Engineer will show up to test the ventilation system. We spend two hours, and use specialized equipment, to measure air flow at various flow settings on the HRV (low, medium, high, etc.) We check the air flow at every single ventilation register in the home, and take the time to adjust the system until it is offering air flow rates that are consistent with our design goals for the home. After you are in the home, if something goes awry, or you don’t see the results that you want when you are cooking or showering, we will want to know about it! We will come back and adjust things until everything is groovy.
[editors note] We received an email from a reader who made some noteworthy observations regarding the efficiency ratings of gas vs. induction cooking~40% to 85-95% respectfully. Also worth mentioning is gas is not a renewable resource. Good points!