brizzad
New Member
Posts:10
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| 30 Aug 2010 06:22 PM |
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I am currently building a house, and had done some research on HRV's... deciding to spend the money on one for the new home. When the rough-ins were being completed, I was surprised to note that they installed bathroom exhaust fans, in addition to the HRV's exhaust points within the bathrooms. (Fully-ducted installation).
Is this typical and what I should expect in a brand-new installation??? My concerns to pass back to the builder & the hvac installer are:
Pressure Issues: Will running the bathroom fans in addition to the HRV potentially create negative pressure issues? I suppose this depends on whether or not the bathroom fans also have an air supply to bring in air as they exhaust it?
No Heat Recovery: The entire purpose of the HRV is to recover the heat from the air, and this will be negated.
Can anyone provide any insight or thoughts on this? |
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JohnyH
Basic Member
Posts:114
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| 31 Aug 2010 07:49 AM |
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When I built the house I'm in now I only had the HRV ducted to the bathrooms, laundry rooom and kitchen, and no extra exhaust fan in the bathrooms! This was 23 years ago maybe the rules have changed since?
Put a switch/timer in the bathroom to turn on the HRV to high speed for 20 minutes while it is in use and a bit of time after!
John |
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brizzad
New Member
Posts:10
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| 31 Aug 2010 10:57 AM |
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JohnyH... that sounds like the scenario I was expecting. We requested 20 minute timers in each bathroom, so I was surprised to find the existance of regular bathroom fans as well. |
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JohnyH
Basic Member
Posts:114
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| 31 Aug 2010 11:59 AM |
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I wouldn't want them?
John |
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brizzad
New Member
Posts:10
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| 31 Aug 2010 01:22 PM |
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Neither do I, but it is too late at this point probably. It unfortunately means I have additional openings in the building envelope that are probably not required. Less insulation, potential for leaks in the future, etc, etc.
Provided the HRV is capable of exhausting humidity from the bathrooms/laundry, etc ... to have bathroom fan controls there as well will only confuse any house guests and they will be redundant. Hopefully in the scenario where the HRV is running, as well as a bathroom fan ... this will now create any pressure issues.
I asked for a technical answer as to why they are there in addition to the HRV exhausts. I am in Alberta, so maybe it is a code-specific thing ... or the HRV they provided is not sized appropriately to exhaust these spaces? Either way this is the info I expect back from them. |
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JohnyH
Basic Member
Posts:114
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| 01 Sep 2010 07:48 AM |
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CMHC site has a research paper on HRV's that I was looking at sometime ago that has a lot of good information on HRV's. I have a PDF file someplace but not a shortcut to the paper, type in HRV on the CMHC site and you should find it! ( I downloaded the FREE paper!) I haven't looked at specific manufacturers or option's but they have become very innovative in the way that they do have sensors and open up the intake larger to allow more air removal in humid area's!
John |
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cmkavala
Veteran Member
Posts:4327
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| 01 Sep 2010 07:56 AM |
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John;
how about a link to the CMHC site? |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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JohnyH
Basic Member
Posts:114
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| 01 Sep 2010 07:59 AM |
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http://www.cmhc-schl.gc.ca/en/co/maho/gemare/gemare_004.cfm
John |
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JohnyH
Basic Member
Posts:114
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| 01 Sep 2010 08:13 AM |
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I you cut and paste on the link below and then do a search for 62015 it should get you there!
https://www03.cmhc-schl.gc.ca/catalog/search.cfm
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Eric Anderson
Basic Member
Posts:441
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| 01 Sep 2010 11:43 AM |
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In my house I have both a Bathroom vent that is about 80 cfm and located directly over the shower and a ERV in the house. The ERV has a stale air intake in the bathroom and in the kitchen
I kind of thought that when it was cold, the ERV or HRV was much more likely to freeze up if it was used to exhaust the very humid air in the bathroom as primary shower humidity control. Yes I know they come with defrost cycles.
Basically when I use the shower I set the vent to 30 min., and let the ERV take care of the rest of the moisture on its normal cycle. To prevent air from reversing into the house I use a well sealed vent (hartland dryer vent). When I put on the range fan to Maximum, I can’t feel any air at the bathroom vent so I don’t think it is a problem.
I do have to be careful with having too many things venting at once causing negative pressure in the house. I can backdraft the woodstove when I first light it if the range vent and or shower vent + dryer is on and I don’t crack a door or window. The ERV actually helps with pressure equalization, whether it is on or off. You can feel air blowing from the ERV vent when the range vent is on.
Cheers,
Eric |
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| Think Energy CT, LLC Comprehensive Home Performance Energy Auditing |
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brizzad
New Member
Posts:10
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| 01 Sep 2010 12:57 PM |
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Thanks for the links JohnyH, I've looked the CMHC site before but I'll have a look again. I did note that the Home Ventilating Institute says @ their bathroom ventilation guide http://www.hvi.org/bguide.html: Continuous ventilation:
Alternatively, ventilation may also be provided on a continuous basis at other rates. This may complement the use of fans to provide the HVI recommended rates. I suppose my main concerns were as Eric Anderson pointed out, there is the potential to cause backdrafting if you are not aware of what/how you are venting, given that additional exhaust fans are involved. |
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brizzad
New Member
Posts:10
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| 01 Sep 2010 01:04 PM |
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They also note in their "How Much Ventilation Do I Need" guide: http://www.hvi.org/resourcelibrary/HowMuchVent.html___________________________________________________________________
Bathrooms – intermittent ventilation
HVI recommends the following intermittent ventilation rates for bathrooms:
| Bathroom size |
Calculation formula |
Ventilation rate required |
| Less than 100 square feet |
1 CFM per square foot of floor area |
A minimum of 50 CFM |
| More than 100 square feet |
Add the CFM requirement for each fixture |
Toilet 50 CFM
Shower 50 CFM
Bathrub 50 CFM
Jetted tub 100 CFM |
- An enclosed toilet should have its own exhaust fan.
- Fans approved for installation in wet areas should be located over the shower or tub whenever possible.
- Bathroom doors need to have at least 3/4" clearance to the finished floor to allow proper entry of makeup air.
- A timer or other control that ensures ventilation continues for a minimum of 20 minutes after each use of the bathroom should be installed in each bathroom.
- For steam rooms, HVI recommends a separate fan located in the steam room that can be turned on after use to clear the heat and humidity.
Bathrooms – continuous ventilation
Continuous ventilation at a minimum rate of 20 CFM may be used in lieu of an intermittent 50 CFM exhaust fan.
____________________________________________________________________
With the last sentance relating to an HRV/ERV for continuous ventilation. I suppose I can run through some calculations on my own here. For the ensuite bathroom, and the other guest bathroom I can understand the additional fans perhaps, if the calculated exhaust flow of the HRV was not sufficient, though cannot determine why a fan would be required for the powder room on the main floor which only has a toilet. Ah well, lots to learn. |
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Dana1
Senior Member
Posts:6991
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| 01 Sep 2010 03:00 PM |
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When the bathroom fans are running, yes, the house is (temporarily) under negative pressure, but it's makeup air path is the bath of least resistance: The HRV system.
If the HRV is set up such that it's constantly drawing/replacing at least 20cfm to the bathroom on a continous basis it'll meet code without a bathroom fan. But that might require an excessive ventilation rate for the whole house to achieve that. Putting a code-minimum 50cfm switched/intermittent bathroom fan in there brings it up to snuff, and you can set the HRV to deliver the necessary ventilation rate for the whole-house and not be reuqired to hype-ventilate the house just to meet code in the bathroom.
Whether you use the bathroom fan or not is up to you, but if it's operated by an occupancy sensor switch or timer-switch so that it can't be accidentally left on for long periods it's not an energy-disaster. But if you insist on a balanced ventilation system with heat recovery, the li'l Panasonic single-room ERV meets code as a bathroom fan:
http://www2.panasonic.com/consumer-electronics/shop/Building-Products/Ventilation-Systems/Energy-Recovery-Ventilators/model.FV-04VE1.S_11002_7000000000000005702#tabsection
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Eric Anderson
Basic Member
Posts:441
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| 01 Sep 2010 03:57 PM |
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The other thing to keep in mind is that a bath fan is a fairly low CFM device usually. My range fan on High is 7 times higher in CFM, the dryer is about twice as high.
IF the bath fan is 80 cfm and you use if for 30 min at a time for 3 people who take showers, that is 3X30X80= 7200 cubic ft of air. Assume a 2000 ft^ 2 story house with a basement and 9 ft ceilings= 1000*(9+9+8)= 26,000 cubic ft of air. 7200/26,000 = 0.28 air changes per DAY.
In other words, the bath fan accounts for 1/3 of an air change per day or 1/24 th of the total minimum recommended ventilation rate of the house. Personally, I wouldn’t stress about this.
On an day with an outside temp of 15 °F and an inside temp of 65°F, to heat 7200 cubic ft of air 50 degrees f, 7200 ft^3* 50° *0.018 btu/ft^3air/degree = 6480 BTU per day. Unless you are going all passive house, you can sefely ignore this.
If you plan to live without AC, having a good method of getting rid of excess latent humidity is a very good idea.
Lots of stuff to stress over in a house, make sure they use good sealed vents on the fans and move on.
Cheers,
Eric
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| Think Energy CT, LLC Comprehensive Home Performance Energy Auditing |
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brizzad
New Member
Posts:10
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| 01 Sep 2010 04:32 PM |
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Those are great comments Eric (& Dana)... and more specifically what I was looking for some reassurance on. I'd expected to hear something like that from my query with the HVAC guys, rather than the response of: 'The bathroom fans are to expel humid air, and the hrv is to circulate air throughout the house' which ended up coming through the site super for the new neighborhood I'm building in.
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brizzad
New Member
Posts:10
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| 14 Sep 2010 03:25 PM |
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Just to follow up on this conversation, here is the response I received from the HVAC System Designer: The HRV is sized for the Principle Ventilation Fan based on the total number of rooms in the home. That work out to 150cfm, the HRV-200 is rated for 152cfm at .5”WC, so if you split that up over about 6 to 7 outlets, each outlet will only pull about 22cfm, which in my opinion is not enough to exhaust the humidity out of the bath rooms. That is why we recommended to leave the bath fans in place to be used as back up for the HRV. There is no concerns for depressurising the home with the bath fans running because all the fuel burning appliance in the home are sealed combustion or direct vent units. The loss of the heat recovery using the bath fans as back up to the HRV shouldn’t be noticed because it will be so minimal even on our coldest of days |
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nolanarcher
New Member
Posts:19
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| 15 Sep 2010 12:43 AM |
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Well that's not encouraging. If it doesn't make a difference, why have the HRV at all?
I live in Calgary, and have been having a really hard time even finding a company who knows what an HRV is, let alone how to install a system. |
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cmkavala
Veteran Member
Posts:4327
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| 15 Sep 2010 07:08 AM |
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Posted By nolanarcher on 15 Sep 2010 12:43 AM
have been having a really hard time even finding a company who knows what an HRV is, let alone how to install a system. You need to go to a bigger HVAC company , "make up air" units are larger versions of HRV / ERVs and are required in ALL commercial buildings in the US. I am just guessing they are also required in Canada too A smaller HVAC company would not be familiar with them |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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Eric Anderson
Basic Member
Posts:441
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| 15 Sep 2010 08:25 AM |
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The HVAC company’s explanation makes sense to me. The thing I would ask for is that the controls for the bathroom fans be on timers. I like the 5,15, 30 minute timers. For me it is very easy, when I want to take a shower, I hit the 30 min button on the fan control, take a shower and the fan shuts itself off later. You can also use humidity sensors or occupant sensors. If you live with the windows open in the summer, you can shut off the HRV, but you still want a bath fan.
Cheers
Eric |
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| Think Energy CT, LLC Comprehensive Home Performance Energy Auditing |
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brizzad
New Member
Posts:10
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| 15 Sep 2010 10:57 AM |
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I am in Calgary as well Nolan. I'm not sure who the HVAC company is, but I'm sure I could find out. Their answer says to me they know what they are doing. I was happy to see the explanation from the HVAC system designer because:
1.) It answered my original questions regarding why the bathroom fans were still there and that some real thought had been put into the reason. (By his calculations, the HRV will only draw 22CFM per outlet. According to the HVI reccommendations that 20CFM of continuous ventilation can suitably replace a 50CFM bath fan. So the HRV provides enough ventilation in the main bath with only a toilet just barely. For the other bathrooms though, he is correct... the bathroom fans will be required to get rid of the humidity generated when the shower/tub are in use).
2.) The answer aligned with Eric's calculations that heat loss from the use of bathroom fans is negligible.
3.) Negative pressure issues from using the bathroom fans will not cause combustion appliances to backdraft since they are either sealed or direct-vented.
His statement "on the coldest of days" was in reference to the heat loss due to using the bathroom fans being negligible. I did not take it as the HRV will not make a difference. While the HRV may not be capable exhausting all the humidity in a short time span when required by itself alone, it will still serve its purpose (I'm hoping) to continuously provide fresh air while at least recovering heat from some of the stale air.
Better to have the bathroom fans installed now, than miss them in the future if I were to find out the HRV does not in fact exhaust humidity sufficiently when using the shower/tub/toilets. I will report back in January/February when the house is done! Having built a home before, being in an area of constant construction was pretty dirty. When we wanted fresh air, having to open a window let in a ton of dirt/dust as was noticed by the window sill a short time after being open. I am hoping the HRV makes a difference in the first year of being in the home so we don't have to let in as much dirt/dust to get fresh air! |
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