Fresh air in the winter, please
October 15, 2013 1:41 AM Subscribe
Mr Uans is convinced that even cracking the window an inch to bring in some fresh air on a cold day allows ALL the heat to escape the bedroom. He says why run the furnace if you are going to open the window? I, on the other hand, very much appreciate a little fresh air and think the heat loss is marginal. Which one of us is right according to the facts, not anecdata? Can you point us to some helpful links that will end the arguing? Thanks!
Technically, any furnace must have a fresh-air intake, by code, so that it maintains a positive pressure differential and the noxious products of combustion, like carbon monoxide, are properly vented up the chimney (or out the high-efficiency hood). Additionally, typical North American construction is going to have a significant amount of airflow leakage, as mentioned by pracowity, e.g. between the framing and the foundation, then up through the walls, and finally out the attic. This leakage is now the subject of great attention for energy efficiency experts, as it is the largest solvable problem for most already-built construction.
Opening windows in the winter seems to be a Northern European thing. I picked it up from my German/Swedish heritage, I suspect. It also dates back to folk medicine concepts about health -- which may have some merit but mostly predates the 19th century and germ theory. (It's a 20th century musical, but 1776 has an amusing hotel-room argument between Franklin and Jefferson on the matter, IIRC.)
But you are probably reacting less to "non-freshness" and more to stuff that is actually in the air, such as VOCs from various plastics in your home. A few things you could try to improve the perceived air quality:
* more plants (fragrant or not to taste)
* a more expensive, and/or more frequently changed furnace filter
* ceiling fans (which usually have a reverse, i.e. winter, setting)
* steam-cleaning carpets can make a BIG difference
* dehumidifier if you have a damp, musty basement (note, a truly wet basement may need more intervention)
In general, to save on heating bills and energy usage, you probably want more insulation, and better sealing, rather than actually letting heat out. You can also build more time outside into your lifestyle, e.g by walking a dog or sitting in a sweater on the porch while you read the paper, etc.
posted by dhartung at 2:39 AM on October 15, 2013 [7 favorites]
Opening windows in the winter seems to be a Northern European thing. I picked it up from my German/Swedish heritage, I suspect. It also dates back to folk medicine concepts about health -- which may have some merit but mostly predates the 19th century and germ theory. (It's a 20th century musical, but 1776 has an amusing hotel-room argument between Franklin and Jefferson on the matter, IIRC.)
But you are probably reacting less to "non-freshness" and more to stuff that is actually in the air, such as VOCs from various plastics in your home. A few things you could try to improve the perceived air quality:
* more plants (fragrant or not to taste)
* a more expensive, and/or more frequently changed furnace filter
* ceiling fans (which usually have a reverse, i.e. winter, setting)
* steam-cleaning carpets can make a BIG difference
* dehumidifier if you have a damp, musty basement (note, a truly wet basement may need more intervention)
In general, to save on heating bills and energy usage, you probably want more insulation, and better sealing, rather than actually letting heat out. You can also build more time outside into your lifestyle, e.g by walking a dog or sitting in a sweater on the porch while you read the paper, etc.
posted by dhartung at 2:39 AM on October 15, 2013 [7 favorites]
Best answer: Might I suggest an approach:
Place a thermometer in the middle of the room and take a reading. Leave the window open and take readings every 30 minutes. Then you can answer it unequivocally for your property.
Opening a window will leak warm air, but not as much as if you use the old sash window trick of opening the top and the bottom a fraction - at that point hot air escapes through the top and cold air is drawn in through the bottom. In other words, the amount of air exchanged is key. so, for example, a windy day will see you lose more heat. If you go to page 8 of the document linked here you can get the maths.
Ventilation rate based on Air change method:
V = ACH * A * H / 60
Where
o V = Ventilation air in CFM
o ACH = Air changes per hour usually 0.15 to 0.5 ACH depending on the construction
of the building
o A = Area of the space in ft2
o H = Height of the room in ft
Note A * H is the volume of the space.
Ventilation rate based on Crack method:
Volume of air = I * A
Where
o V = Ventilation air in CFM
o I = Infiltration rate usually 0.15 cfm/ft2
o A = Area of cracks/openings in ft2
posted by MuffinMan at 3:06 AM on October 15, 2013 [5 favorites]
Place a thermometer in the middle of the room and take a reading. Leave the window open and take readings every 30 minutes. Then you can answer it unequivocally for your property.
Opening a window will leak warm air, but not as much as if you use the old sash window trick of opening the top and the bottom a fraction - at that point hot air escapes through the top and cold air is drawn in through the bottom. In other words, the amount of air exchanged is key. so, for example, a windy day will see you lose more heat. If you go to page 8 of the document linked here you can get the maths.
Ventilation rate based on Air change method:
V = ACH * A * H / 60
Where
o V = Ventilation air in CFM
o ACH = Air changes per hour usually 0.15 to 0.5 ACH depending on the construction
of the building
o A = Area of the space in ft
o H = Height of the room in ft
Note A * H is the volume of the space.
Ventilation rate based on Crack method:
Volume of air = I * A
Where
o V = Ventilation air in CFM
o I = Infiltration rate usually 0.15 cfm/ft
o A = Area of cracks/openings in ft
posted by MuffinMan at 3:06 AM on October 15, 2013 [5 favorites]
Place a thermometer in the middle of the room and take a reading. Leave the window open and take readings every 30 minutes.
If you're on a thermostat, the room may not get colder because you'll be running the furnace more.
posted by Obscure Reference at 4:20 AM on October 15, 2013 [5 favorites]
If you're on a thermostat, the room may not get colder because you'll be running the furnace more.
posted by Obscure Reference at 4:20 AM on October 15, 2013 [5 favorites]
Sorry, yes - you switch off the heating before you do this or it doesn't make sense!
posted by MuffinMan at 4:30 AM on October 15, 2013 [1 favorite]
posted by MuffinMan at 4:30 AM on October 15, 2013 [1 favorite]
I agree that cracking the windows loses a ton of heat.
If the air really isn't fresh, you could have an air-to-air heat exchanger installed to allow some fresh air into the furnace's make up air so you are always getting a little fresh air.
posted by gjc at 4:32 AM on October 15, 2013
If the air really isn't fresh, you could have an air-to-air heat exchanger installed to allow some fresh air into the furnace's make up air so you are always getting a little fresh air.
posted by gjc at 4:32 AM on October 15, 2013
Agree with previous posters about heat loss.
Your use of the word "fresh" is telling. We've become acclimated to the idea that cool is equivalent to fresh and clean. The connection probably comes from that many people experience colder temperatures as refreshing. Personal product producers have capitalized on this - many face washes that are supposed to leave your skin "feeling fresh" (and clean) actually have a bit of menthol, which makes your skin feel cooler. We also associate warmth with fragrance and odorance (the latter for good reason) - ex. fresh cookies from the oven, but not clean. I don't think anyone would say that a hot oven is fresh, even if it is very clean.
Assuming that your indoor air quality is good (eg, clean), if you want to replicate that refreshing aspect of having a window open, maybe a fan would be sufficient? You get a bit of airflow, which when it blows across you might feel cooler. You aren't changing the temperature of the room, just the distribution of the air.
posted by troytroy at 5:26 AM on October 15, 2013 [3 favorites]
Your use of the word "fresh" is telling. We've become acclimated to the idea that cool is equivalent to fresh and clean. The connection probably comes from that many people experience colder temperatures as refreshing. Personal product producers have capitalized on this - many face washes that are supposed to leave your skin "feeling fresh" (and clean) actually have a bit of menthol, which makes your skin feel cooler. We also associate warmth with fragrance and odorance (the latter for good reason) - ex. fresh cookies from the oven, but not clean. I don't think anyone would say that a hot oven is fresh, even if it is very clean.
Assuming that your indoor air quality is good (eg, clean), if you want to replicate that refreshing aspect of having a window open, maybe a fan would be sufficient? You get a bit of airflow, which when it blows across you might feel cooler. You aren't changing the temperature of the room, just the distribution of the air.
posted by troytroy at 5:26 AM on October 15, 2013 [3 favorites]
Interestingly, some of this idea about fresh air is tied to the 1918 flu pandemic, which killed a whole bunch of people. Ventilation was thought of as a way to prevent the spread of the disease, and accordingly many buildings were fitted with bigger heating systems capable of keeping them warm even with windows open in winter.
Regardless of whether this makes sense in objective healthwise terms, I sympathize with you; the mixing of cool and warm air, the smells and sounds from outside can be delicious. You're definitely losing heat this way. How much heat you're losing depends on how wide you open the window, for how long, and the difference between the outdoor and indoor temperatures, but it unquestionably will raise your heat bills. It's up to you whether it's worth it.
posted by jon1270 at 5:58 AM on October 15, 2013 [3 favorites]
Regardless of whether this makes sense in objective healthwise terms, I sympathize with you; the mixing of cool and warm air, the smells and sounds from outside can be delicious. You're definitely losing heat this way. How much heat you're losing depends on how wide you open the window, for how long, and the difference between the outdoor and indoor temperatures, but it unquestionably will raise your heat bills. It's up to you whether it's worth it.
posted by jon1270 at 5:58 AM on October 15, 2013 [3 favorites]
Best answer: Let's say you open the window one inch as described - a typical North American double-hung window is, what, 18 inches wide? You can do a quick first-order approximation of how much energy you're wasting using this.
From here, we can determine the flow rate of outside air into your home. For a single open window, they describe the volumetric flow rate as V_dot = 0.05*A*v_ref. You say you're in Toronto, so let's call your general vicinity "Urban", which gives us a reference wind velocity (v_ref) coming through your window in December of about 6.5 mph. The open area of the window is 18 square inches or 0.125 square feet; 6.5 mph is 572 feet per minute so you're looking at a rough estimate of 71.5 cubic feet per minute of cold air entering your house.
Now, the average temperature in Toronto in December is 27F. To figure out how much energy you need to warm up 71.5 CFM of cold air to room temperature, we use Q = m_dot * Cp * (T_f - T_i), where m_dot is the mass flow rate of the air, Cp is its heat capacity, and T_f and T_i are the final and initial temperatures, respectively. Cp for ideal air is nominally 1 kJ/kg-K, so we'll use that. 71.5 CFM of air at 27F is roughly 2.6 kg/min (using the density of air at 27F and converting back to metric). Room temperature is a standard 70F or 21C (27F is about -3C), so then Q is about 63 kJ per minute.
So what does this mean? Well, if you heat your home with natural gas (low heating value of 47 MJ/kg), you're burning about 0.08 kg per hour to keep that window open, or about 3.6 cubic feet of gas per hour. Looking around online, I'm seeing gas costs in Toronto at about 17 cents per cubic meter, which means it's costing you about 2 cents per hour to keep the window open, or about $14.40 per month, and probably a lot higher if you're using heating oil instead of gas.
posted by backseatpilot at 6:03 AM on October 15, 2013 [8 favorites]
From here, we can determine the flow rate of outside air into your home. For a single open window, they describe the volumetric flow rate as V_dot = 0.05*A*v_ref. You say you're in Toronto, so let's call your general vicinity "Urban", which gives us a reference wind velocity (v_ref) coming through your window in December of about 6.5 mph. The open area of the window is 18 square inches or 0.125 square feet; 6.5 mph is 572 feet per minute so you're looking at a rough estimate of 71.5 cubic feet per minute of cold air entering your house.
Now, the average temperature in Toronto in December is 27F. To figure out how much energy you need to warm up 71.5 CFM of cold air to room temperature, we use Q = m_dot * Cp * (T_f - T_i), where m_dot is the mass flow rate of the air, Cp is its heat capacity, and T_f and T_i are the final and initial temperatures, respectively. Cp for ideal air is nominally 1 kJ/kg-K, so we'll use that. 71.5 CFM of air at 27F is roughly 2.6 kg/min (using the density of air at 27F and converting back to metric). Room temperature is a standard 70F or 21C (27F is about -3C), so then Q is about 63 kJ per minute.
So what does this mean? Well, if you heat your home with natural gas (low heating value of 47 MJ/kg), you're burning about 0.08 kg per hour to keep that window open, or about 3.6 cubic feet of gas per hour. Looking around online, I'm seeing gas costs in Toronto at about 17 cents per cubic meter, which means it's costing you about 2 cents per hour to keep the window open, or about $14.40 per month, and probably a lot higher if you're using heating oil instead of gas.
posted by backseatpilot at 6:03 AM on October 15, 2013 [8 favorites]
Do you have access to your electricity meter? I'd run a few overnight experiments during a time with relatively consistent outdoor temperature: say, three nights with the window cracked and three with it closed, everything else constant.
After you've gathered that data, if the cracked window gives you pleasure, and he does not mind it other than the heating inefficiency, perhaps you can identify ways to offset the energy loss: do more laundry on "cold," shut off the power strips on your power-draining electronics, check your vents and filters, etc. (your local power company probably has a good checklist, and many offer subsidies for energy conservation products/services).
I'm sure there are things he does that give him pleasure that are not the most energy- or cost-optimal choices. Hopefully you two can agree to the sweet spot on this one, too.
posted by argonauta at 6:16 AM on October 15, 2013 [1 favorite]
After you've gathered that data, if the cracked window gives you pleasure, and he does not mind it other than the heating inefficiency, perhaps you can identify ways to offset the energy loss: do more laundry on "cold," shut off the power strips on your power-draining electronics, check your vents and filters, etc. (your local power company probably has a good checklist, and many offer subsidies for energy conservation products/services).
I'm sure there are things he does that give him pleasure that are not the most energy- or cost-optimal choices. Hopefully you two can agree to the sweet spot on this one, too.
posted by argonauta at 6:16 AM on October 15, 2013 [1 favorite]
The open area of the window is 18 square inches or 0.125 square feet; 6.5 mph is 572 feet per minute so you're looking at a rough estimate of 71.5 cubic feet per minute of cold air entering your house.
In principle I like backseatpilot's calcuation approach, but if you only open one window then it probably overestimates the cost. 71.5 cfm can only come in that window if 71.5 cfm leaves the house through other openings. Opening one window on one side of the house will have substantially less impact than opening 2 of them on opposite sides.
posted by jon1270 at 6:52 AM on October 15, 2013
In principle I like backseatpilot's calcuation approach, but if you only open one window then it probably overestimates the cost. 71.5 cfm can only come in that window if 71.5 cfm leaves the house through other openings. Opening one window on one side of the house will have substantially less impact than opening 2 of them on opposite sides.
posted by jon1270 at 6:52 AM on October 15, 2013
if you only open one window then it probably overestimates the cost
The reference I linked to accounts for that. But, like I said, first approximations and all.
posted by backseatpilot at 7:09 AM on October 15, 2013
The reference I linked to accounts for that. But, like I said, first approximations and all.
posted by backseatpilot at 7:09 AM on October 15, 2013
Are you two really having this as a theoretical conversation? Or are you trying to figure out if it's okay to open the window? Whatever the numbers say I think only you two can figure out if cracking a window is making it feel colder or not. And I doubt he thinks it lets ALL the heat out, literally. If so, the temperature would feel no different inside than outside. Perhaps he means that it feels colder with the window cracked and it's not worth the loss of heat given how much heat you do have. If he feels no colder with the window cracked and is just arguing from how it's supposed to be, that doesn't make much sense at all. Either it feels colder or it doesn't. Perhaps you feel less cold than he does already, and think the loss of heat is worth it for the enjoyment you get from the feeling of a little fresh air. Perhaps he values warmth over fresh air.
posted by Blitz at 12:54 PM on October 15, 2013 [1 favorite]
posted by Blitz at 12:54 PM on October 15, 2013 [1 favorite]
I don't see the conflict here, can't you just turn off the furnace while you have the window open? He wants the furnace off when the window is open, you want fresh air, you both get what you want.
As a bonus, you'll find out pretty quick how much heat is lost for your very own house. I suspect it will be somewhere in between "all the heat" and "marginal".
posted by yohko at 3:40 PM on October 15, 2013
As a bonus, you'll find out pretty quick how much heat is lost for your very own house. I suspect it will be somewhere in between "all the heat" and "marginal".
posted by yohko at 3:40 PM on October 15, 2013
If this is more about fresh air rather than a cool breeze, an air purifier and/or ionizer might provide the freshness you desire without the cold air and heat loss of an open window.
posted by katemcd at 4:40 PM on October 15, 2013
posted by katemcd at 4:40 PM on October 15, 2013
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Could you open the windows wide for just a minute or two to let the whole room get a blast of cold fresh air -- long enough to replace pretty much the whole volume of air in the room -- and then close the windows tight? You would then have a roomful of fresh air that you could heat with the help of the heat that still remains in the furniture, walls, floors, etc., which have not had time to cool all the way down. Would that make you both happy?
posted by pracowity at 2:09 AM on October 15, 2013 [8 favorites]