What's a renter to do? Air sealing can be low cost and effective

After over thirty years of home ownership, I found myself a renter on MV. This made good sense to us - we didn't want to buy a house while we owned our NH home, and we got to try out the cohousing life without making a more permanent commitment. For the first time since I was a kid, I was living with an oil boiler for my heat and domestic hot water (DHW).

If you arrived at this blog, you don't need to be convinced that it's a worthy goal to burn less fossil fuels. That's not the only reason to want the oil system gone, though. Have you ever been in a house where there has been a spill of fuel oil? It soaks into the ground below. You can smell it for decades. The cost of clean up can exceed the value of the house.

For the meantime, though, we were going to be heating our water and the house with oil. We'd started with the 330 gallon oil tank 3/4 full at the beginning of June, and I didn't want to buy any more oil through the winter. We had data from the last renter who'd been there and they'd used an average of 435 gallons of oil annually over a two year period. We had some work to do, then, to meet our no more oil goal.

Heat in houses is lost by conduction through the foundation (yes, heat flows down - it flows from hot to cold), walls, and roof; by conduction through the windows and doors; and by air leaking into and out of the house. It would be an unusual situation in which a renter would add insulation or change windows in a house (although they might convince the landlord to implement upgrades that they agree to pay more rent for). But the air leakage can easily be 30% of your heating bill, and it's the easiest, and least expensive, to address.

The way building performance professionals measure air leakage is with an instrument called a blower door. The most popular product is made by the Energy Conservatory, it's called the Minneapolis Blower Door. An expandable frame fits into an exterior door opening, and it is covered with a nylon shroud, into which a large calibrated fan is installed. A digital manometer measures the pressure drop across the fan and the pressure drop from indoors to outdoors. The idea is to use the blower door to depressurize the house to a fixed pressure below outdoors (typically 50 pascals in homes) and measure how much air it takes to sustain this pressure difference. The tighter the house, the less air the blower moves to reach 50 pascals. A MN blower door will move over 6,000 cubic feet of air per minute (CFM) (that's quite a gale). Some houses are so leaky that you need more than one blower door to bring them to a 50 pascals pressure difference. Others, like houses built to the Passive House standard, might require under 100 CFM. (Disclosure - I am a Certified Passive House Consultant, and probably certifiable in other ways as well, so I'm a True Believer in very tight houses, and a mechanical ventilation system.)

Being a building geek, I own a blower door, so it was a simple matter to test the house. Besides using the blower door to get a CFM at 50 pascals measurement (called CFM50 in the trade), we can use them to find leaks, and to assess which part of the house is leaking the most. When I look for leaks, I use a theatrical fog machine, which I'll describe in a future post. The results of my testing showed me that the house was 919 CFM50. This is better than the typical new house but leakier than I expected. I then used a technique developed by Michael Blasnik called Zonal Pressure Diagnostics. This told me that the leakage between the house and the outdoors through the basement were four times higher than the leakage through the attic. This helps focus attention on the places where the largest improvements may be made.

Some of the leakage locations were obvious. There were big gaps below the exterior doors. The attic hatch had a cover that was too small, and was un-weather-stripped, and had no insulation to boot. As is not uncommon, this last was despite the construction drawings showing a weather-stripped and insulated hatch cover. In the basement, there were holes I could see outdoors through around the door at the base of the bulkhead stairs (though, at least this house had a door at the base of the bulkhead -  a common omission) and around the triple awning window at the south end of the basement. In about two hours of work, and maybe $30-50 of materials, I dropped the leakage from 900 to 650 CFM50. This is work that probably has a one year payback. I installed a door sweep on the exterior door; weatherstripped the hatch and made a 4 inch foam insulation plug to go on top of it; and used foam sealant in a Pageris foam gun (this link is to the professional tool, but there are less costly homeowner versions) and some caulk for the small gaps (less than 1/4 inch) to seal at the basement window and door.

It's not beautiful, but it works.

Comments

[Abe]

In my experience, air sealing has been a very rewarding investment in my rented apartment. It is a renovated barn, and had all kinds of gaps around timbers where they joined other timbers or butted up against sheetrock.

The first winter I used over 400 gallons of propane, which motivated me to spend a couple of days sealing gaps with spray foam, caulk, backer rod, and even some wooden blocks to cover the largest holes. I also dropped the thermostat 5 degrees the next winter, and saw my fuel usage drop significantly. I did a bit more sealing the next year, and since then I've burned about 200 gallons/year.

Admittedly,the apartment below mine is heated, so I think lowering my thermostat has an even larger affect than in a stand-alone unit. Not only is the heat loss from my apartment to the outdoors decreased, but the thermal flux across my floor into my space from the apartment below increases as my air temperature drops.

An added benefit is that the cigarette smoke odors from neighbors have gone down from the air sealing as well--since the entire building structure is connected in strange and leaky ways, I have tried to seal all joints even in interior walls.

[Marc]

Great point about the reduction in smoke and odors caused by air transfer! Thanks, Abe.

[Harold Orr]

An interesting project but is "stealing" heat from your neighbor cricket? What does 650 CFM50 represent in air changes per hour at 50pascals? (ACH50) After you had done all the air sealing where were the major leaks remaining? Do you now need an A-A heat exchanger? How much further tightening would be needed to make an A-A heat exchanger cost effective? You have reduced the leakage but you have also increased indoor pollution. Is this going to be a health problem?

[Marc]

Harold, it's GREAT to "see" you! In the words of The Carpenters, We've Only Just Begun. 650 CFM50 in this house is a bit over 2 ACH50. We have mechanical ventilation in the exhaust fan for the composting toilet, and one of my investigations will be whether I can run that necessary exhaust through a heat recovery ventilator without detectable air quality issues. I hope this week to remove the second of two indoor air quality problems - a gas range. The first was the oil boiler. Stay tuned!

[Marc]

Oh - the bulk of the remaining leakage I believe from the zonal pressure diagnostic work is in the basement at the sill and rim joist area. Although we have lots of intentional holes - a direct vent gas heater that will be going, a clothes dryer, the oil boiler inlet and vent.

[Abe]

Marc, I'm glad to hear you talking about heat recovery from composting toilet exhaust--it's something that's been nagging at me, too. If you try hooking it to an air-to-air exchanger, I'd love to hear how it works. I imagine the filter on the exchanger filling up pretty quickly, since the exhaust can be damp and dusty. Have you considered building your own exchanger out of coaxial ducts, with the air intake running inside of the exhaust pipe? I don't know how efficient that would be, but it would require no filtration of the exhaust, just perhaps a cleaning of the pipe every decade or so.

P.S. @Harold: I did consider the ethics of keeping my apartment cooler than my downstairs neighbor's, but decided that I wasn't going to burn lots of extra propane heating my space beyond my needs, just to keep his ceiling slightly warmer. I wouldn't do it if it were zero-sum--if every gallon I saved cost him a gallon extra--but since I share four walls and a cathedral ceiling with the outdoors and only one floor/ceiling with my neighbor, I feel fine about keeping my place at the temperature I prefer. But yes, it is true that I am profiting slightly at another person's expense.

[Heating and Plumbing]

Never got to work with such situation, this looks little bit weird as the finishing doesn't looks that good to me but still as it works would love to try out someday.

[efficient gas furnace]

I have never heard about air sealing. By this post i think air sealing is necessary for our homes. It reduces smoke caused by air transfer. I would like to try this one day. Thanks for sharing.