Losing Heat Through Bathroom Exhaust Fan
Posted on January 29, 2009 – 8:04 pm by admin
If there is one thing that I have noticed during this winter, it’s that the bathroom is really cold in the morning. I keep the door closed because I want to concentrate the heat, so that might be the reason. Either way, the whole thing got me thinking.
Can bathroom exhaust vents cause your house to lose heat? I am thinking yes. I did a Google search on this and came across a good article on “Ask The Builder” entitled, “Bathroom Exhaust Fan Leaks Cold Air.” It pretty much covered what I was thinking.
Basically, a bathroom exhaust fan is simply a fan attached to a hose that leads outside. The fan pushes the moist air you create from taking a shower outside, so you don’t rot everything in your bathroom. Some of the fancy fans have lights in them and I am told that the fans vary in quality. I guess they are supposed to have flaps in them too. The flaps stop the cold outside air from leaking directly into your bathroom and house.
I just walked into the bathroom to see if any cold air was leaking through the fan. I put my hand up to the vent and didn’t feel any cold air. Since that felt okay, I pulled down the attic door and went upstairs to see what that looked like. I saw both bathroom vent hoses leading outside. Nothing seemed too out of place.
Now that I am downstairs, I am thinking that I didn’t really do much to see if there was a problem. I mean, I still have to take the vent cover off to see if the vent flap is closing nice and snug. If not, I have to fix that. Then, I would like to cover the exposed vent hoses with insulation. An exposed vent hose in a cold attic can cause the air in the hose to get cold. That air can enter the house if the vent flap isn’t working correctly. Do you see where I am heading with this? I guess it doesn’t help that the boiler is kicking on and off all night, creating a vacuum in the house. Cold air is probably being pulled in through those vents.
I might need to do some more exploration to see if there is some sort of a “makeup air intake port” anywhere around. If not, I probably need to put one in.
Now, I admit, I am no expert at this. Any advice would be appreciated.
6 Responses to “Losing Heat Through Bathroom Exhaust Fan”
By oshea12566 on Jan 31, 2009 | Reply
I want more photos of empty roads!
By jayadmin on Jan 31, 2009 | Reply
There, there. You may have to wait until spring for that. The roads are pretty ugly right now.
By ben i on Jun 12, 2009 | Reply
i think you might be getting it wrong. it wouldnt be so much that cold air leaks in, than the heat leaking out. all the warmth would be going out of those exaust vents i think. i have just been thinking a similar thing about the ceiling exaust fan i have in the kitchen. our house is pretty open plan, so theres nothing really separating the lounge from the kitchen and the hall. which leads to all the bed rooms. so heat from anywhere would most likely be going straight up out of the kitchen exaust fan.
By Bazz on Aug 27, 2009 | Reply
Hi, i also think its your heat escaping rather then cold coming in. As the hot air rises from inside the house, the vent if open will funnel out your accumulated warm air bringing in cold air from floor level usualy. You should feel warm air at vent not cold.
By Lee on Dec 16, 2009 | Reply
Actually, depending on the prevailing winds at your site, cold air may blow in, or warm air may leak out. Many bath vents can be pulled down an inch or so since they have little clips holding them in place. If you are concerned about air flowing through the vent, just put a page of a magazine behind the fan grille and lock it in place. Then remove the page when your are showering and using the fan. It worked for me!
By H.O. Electric on Jan 31, 2010 | Reply
As the trend to larger spa-like bathrooms continues to gain in popularity, the need for proper ventilation becomes more important. While many people are tired of their noisy and in effective bath fan – not many people know how to properly size a fan to their needs.
There are a few different ways to calculate the number of Cubic Feet Per Minute (CFM) of air movement needed to properly ventilate a bathroom. Make sure you check out the end of the article and read about static pressure. A long duct run from the fan to the outside can skew your calculations.
METHOD 1
This method works on the assumption that the goal for bathroom ventilation is 8 complete air changes per hour. Take your square footage x ceiling height to get the total cubic feet to be ventilated.
Example: Bathroom measures 10 feet wide and 12 feet long. It has 8 foot ceilings. So 10 x 12 x 8 = 960 cubic feet.
We take the cubic feet and divide by 60 – which is the number of minutes in an hour. We take the result and multiply by 8 (remember, our target is 8 complete air changes each hour). The complete equation is as follows:
STEP 1
10 ft X 12 ft X 8 ft = 960 cubic feet.
STEP 2
960 divided by 60 = 16.
STEP 3
16 x 8 = 128
So – we need 128 CFM of air movement to properly ventilate this bathroom. Assuming there is not and excessively long or twisting duct run to the outside – we would select a fan that moves somewhere around 130 CFM or higher. Examples would be the Panasonic FV-15VQ4 or Broan QTXE150FLT, both of which are rated at 150 CFM. If an inline fan is desired – the Fantech FR 110 would suffice.
METHOD 2
This method is a simple one – for bathrooms under 100 square feet. According to guidelines of HVI (Home Ventilating Institute) baths 100 square feet or smaller require one CFM per square foot of bathroom – with a minimum of 50 CFM.
So – if you have a 7 foot by 9 foot bath – you need 63 CFM. It doesn’t get any simpler than this. Most conventional ceiling insert fans, however, are rated either 50 or 80 CFM – so you will have to round up or down (rounding up preferred).
METHOD 3
This method of calculation is designed for bathrooms over 100 square feet and factors in the number of fixtures in the bath (toilets, showers, tubs). The rules are:
* Allow 50 CFM for each standard toilet, shower or tub
* Whirlpool and jetted tubs need 100 CFM
So – if you have 1 toilet (50 CFM), 1 shower (50 CFM) and 1 whirlpool tub (100 CFM) – you will need a 200 CFM Fan. The Pansonic
How to Size a Large Bathroom Ventilation Fan
As the trend to larger spa-like bathrooms continues to gain in popularity, the need for proper ventilation becomes more important. While many people are tired of their noisy and innefective bath fan – not many people know how to properly size a fan to their needs.
There are a few different ways to calcuate the number of Cubic Feet Per Minute (CFM) of air movement needed to properly ventilate a bathroom. Make sure you check out the end of the article and read about static pressure. A long duct run from the fan to the outside can skew your calculations.
METHOD 1
This method works on the assumption that the goal for bathroom ventilation is 8 complete air changes per hour. Take your square footage x ceiling height to get the total cubic feet to be ventilated.
Example: Bathroom measures 10 feet wide and 12 feet long. It has 8 foot ceilings. So 10 x 12 x 8 = 960 cubic feet.
We take the cubic feet and divide by 60 – which is the number of minutes in an hour. We take the result and multiply by 8 (remember, our target is 8 complete air changes each hour). The complete equation is as follows:
STEP 1
10 ft X 12 ft X 8 ft = 960 cubic feet.
STEP 2
960 divided by 60 = 16.
STEP 3
16 x 8 = 128
So – we need 128 CFM of air movement to properly ventilate this bathroom. Assuming there is not and excessively long or twisting duct run to the outside – we would select a fan that moves somewhere around 130 CFM or higher. Examples would be the Panasonic FV-15VQ4 or Broan QTXE150FLT, both of which are rated at 150 CFM. If an inline fan is desired – the Fantech FR 110 would suffice.
METHOD 2
This method is a simple one – for bathrooms under 100 square feet. According to guidelines of HVI (Home Ventilating Institute) baths 100 square feet or smaller require one CFM per square foot of bathroom – with a minimum of 50 CFM.
So – if you have a 7 foot by 9 foot bath – you need 63 CFM. It doesn’t get any simpler than this. Most conventional ceiling insert fans, however, are rated either 50 or 80 CFM – so you will have to round up or down (rounding up preferred).
METHOD 3
This method of calculation is designed for bathrooms over 100 square feet and factors in the number of fixtures in the bath (toilets, showers, tubs). The rules are:
* Allow 50 CFM for each standard toilet, shower or tub
* Whirlpool and jetted tubs need 100 CFM
So – if you have 1 toilet (50 CFM), 1 shower (50 CFM) and 1 whirlpool tub (100 CFM) – you will need a 200 CFM Fan. The Pansonic FV-20VQ3 would work well in this bathroom. An inline fan kit that would work well in this bathroom is theFantech PB 230-2. This kit includes a 200 CFM fan and allows for 2 exhaust grilles in the ceiling.
Static Pressure and Duct Run:
A ventilating fan must overcome resistance when pushing air from the inlet, through the duct, to the outside of the building. This resistance is known as static pressure. The amount of static pressure depends on the duct length, type of duct, elbows and the roof jack or wall cap. Essentially, the more elbows, turns, duct length, etc. that you have – the more static pressure will be present and less effective CFM you will get out of your fan.
Panasonic provides some tools to calculate the model needed to ventilate properly after factoring in duct lenth, duct type, elbow, type of exterior vents, etc. As you might suspect – the end result of the calculations only leads you to select their fans. While it is possible to use air duct calculators and other tools to precisely determine effective CFMs you will get out of a fan – it is probably OK to simply round up to a larger fan if you know you don’t have a straight duct run to the outside would work well in this bathroom. An inline fan kit that would work well in this bathroom is theFantech PB 230-2. This kit includes a 200 CFM fan and allows for 2 exhaust grilles in the ceiling.
Static Pressure and Duct Run:
A ventilating fan must overcome resistance when pushing air from the inlet, through the duct, to the outside of the building. This resistance is known as static pressure. The amount of static pressure depends on the duct length, type of duct, elbows and the roof jack or wall cap. Essentially, the more elbows, turns, duct length, etc. that you have – the more static pressure will be present and less effective CFM you will get out of your fan.
Panasonic provides some tools to calculate the model needed to ventilate properly after factoring in duct length, duct type, elbow, type of exterior vents, etc. As you might suspect – the end result of the calculations only leads you to select their fans. While it is possible to use air duct calculators and other tools to precisely determine effective CFMs you will get out of a fan – it is probably OK to simply round up to a larger fan if you know you don’t have a straight duct run to the outside.