joeldunn21
New Member
Posts:23
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| 07 Mar 2013 01:05 AM |
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My home is being built with OSB SIPs this spring in west central MN.
I have 2 questions that I can't find good answers for. Hopefully some of you with SIPs experience can weigh in on these questions and help me figure out what to do!
1) Does a kitchen range vent hood need a make-up air supply (~200-400 cfm)? If so, what is the best way to accomplish this?
(I'm not interested in cracking a kitchen window in MN in January! I also don't want a backdraft in the living room fireplace!)
2) Would you recommend installing individual bathroom fans, having HRV timers in each bathroom, or both? What are the benefits/drawbacks of each option?
Thanks for the help!
Joel |
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ICFHybrid
Veteran Member
Posts:3039
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| 07 Mar 2013 09:12 AM |
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If your house is built tight, then, yes, you are going to need a source of make-up air to avoid backdrafting the fireplace and any gas burning appliances you have. Outside is the only place you can get it from. All things considered, it's probably best to get it locally, from the kitchen because that will affect fewer places in the house when you admit that January air. Some people crack a window and some people use a fan to bring it in actively. I have a skylight nearly directly above the range vent with an opener that will open when the hood fan is turned on. I also have a sunroom in close proximity to the kitchen, also with a motorized window. It has a volume of 2,000 cubic feet, so, in theory, I could run my hood at 450 cfm for a few minutes, bringing cold Winter air in and displacing conditioned (warm) air in from the sunroom. After a while, the sunroom will have warmed the cold air again..... |
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cmkavala
Veteran Member
Posts:4327
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| 07 Mar 2013 10:38 AM |
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outside air kits for fireplaces are not sufficient |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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joeldunn21
New Member
Posts:23
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| 12 Mar 2013 02:08 PM |
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Anyone with thoughts on bathroom vents? Are individual bathroom fans necessary, or would HRV timers in the bathrooms be sufficient? |
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Lbear
Veteran Member
Posts:2740
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| 12 Mar 2013 05:43 PM |
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Posted By joeldunn21 on 12 Mar 2013 02:08 PM
Anyone with thoughts on bathroom vents? Are individual bathroom fans necessary, or would HRV timers in the bathrooms be sufficient?
Here is what I am going to use: AldesThis way you get your bathroom venting and your HRV needs met with one unit. You also don't have to poke numerous holes in your roof to run fan duct work for each bathroom. Typical bathroom vent fans have always been a necessary evil and they are a big energy waste since they are open to the outside air 100% of the time. They are basically a hole in your roof and the conditioned air just funnels right out like a chimney. Here in AZ you get scorpions and crickets that use the bathroom vent fan to gain access to the home. They simply crawl in through the roof vent and drop down into the bathroom. They try and put window screen around the inside vent but it never works because the vent cover is never flush with the drywall and a scorpion will always get through. A buddy of mine has this problem and he gets around 1-2 scorpions per day come into his home. Getting stung is a monthly norm.  The above product is a great alternative to energy wasteful bathroom fans and it also satisfies the HRV needs of the home. I will have one in each bathroom and one in the kitchen area (not near the cooking area). The fresh air returns will be in the vaulted open areas of the home. You don't want the fresh air return blowing on you directly because in a cold winter, even though it is "conditioned" HRV air, it will still be colder than the interior air based on the efficiency of the HRV unit. It would feel like a cold draft if you had the return facing you in a master bedroom situation. |
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Innova
Basic Member
Posts:121
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| 14 Mar 2013 08:21 AM |
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If your building code will allow, I would suggest a duct free bathroom fan, NuTone makes one that can be installed in the bathroom ceiling or wall with no penetration to the outside. If you are installing a ducted AC, you could consider installing a supply vent in the bathroom and eliminate the fan. Another condsideration is to try and configure your interior layout with bathrooms on an outside wall to allow for installation of a small window, preferably in or near the shower. |
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pcastleberg
New Member
Posts:13
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| 14 Mar 2013 11:37 AM |
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Posted By Lbear on 12 Mar 2013 05:43 PM
Posted By joeldunn21 on 12 Mar 2013 02:08 PM
Anyone with thoughts on bathroom vents? Are individual bathroom fans necessary, or would HRV timers in the bathrooms be sufficient?
Here is what I am going to use:
Aldes
This way you get your bathroom venting and your HRV needs met with one unit. You also don't have to poke numerous holes in your roof to run fan duct work for each bathroom.
Typical bathroom vent fans have always been a necessary evil and they are a big energy waste since they are open to the outside air 100% of the time. They are basically a hole in your roof and the conditioned air just funnels right out like a chimney. Here in AZ you get scorpions and crickets that use the bathroom vent fan to gain access to the home. They simply crawl in through the roof vent and drop down into the bathroom. They try and put window screen around the inside vent but it never works because the vent cover is never flush with the drywall and a scorpion will always get through. A buddy of mine has this problem and he gets around 1-2 scorpions per day come into his home. Getting stung is a monthly norm.
The above product is a great alternative to energy wasteful bathroom fans and it also satisfies the HRV needs of the home. I will have one in each bathroom and one in the kitchen area (not near the cooking area). The fresh air returns will be in the vaulted open areas of the home. You don't want the fresh air return blowing on you directly because in a cold winter, even though it is "conditioned" HRV air, it will still be colder than the interior air based on the efficiency of the HRV unit. It would feel like a cold draft if you had the return facing you in a master bedroom situation.
I like the look of those LBear, thanks for posting. It makes sense if you are building a tight house you are going to need air exchange anyway so why not pull the air from the areas that you need to ventilate anyway!
I would think you could install one of the inlets in the kitchen area where the rangehood would go and install the a timer there as well so that when you need to operate the range hood it would be doing it via the air exchange system.
This way you have less or no roof penetrations and you also are capturing the heat from the expelled air and transferring it to the incoming air.
Very good concept IMO. |
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Lbear
Veteran Member
Posts:2740
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| 14 Mar 2013 11:52 AM |
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Posted By pcastleberg on 14 Mar 2013 11:37 AM
I like the look of those LBear, thanks for posting. It makes sense if you are building a tight house you are going to need air exchange anyway so why not pull the air from the areas that you need to ventilate anyway!
I would think you could install one of the inlets in the kitchen area where the rangehood would go and install the a timer there as well so that when you need to operate the range hood it would be doing it via the air exchange system.
This way you have less or no roof penetrations and you also are capturing the heat from the expelled air and transferring it to the incoming air.
Very good concept IMO.
Do NOT install an inlet where the range hood would go. The reason is that grease/oil will get sucked into the duct work and it will cause problems to the HRV unit. You can install an inlet in the kitchen but NOT in the area where a range hood would go. Somewhere away from where cooking grease/oil can be pulled in. The less roof penetrations the better. Not only from an energy standpoint but also from a better weatherproofing standpoint. Less holes in the roof means less penetrations to seal and less leaks to deal with. I would install a unit in each bathroom and then one in either the laundry/mechanical room or in a non-cooking area of the kitchen. The fresh air returns would go into open areas or hallways. |
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cmkavala
Veteran Member
Posts:4327
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| 14 Mar 2013 11:57 AM |
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Posted By Innova on 14 Mar 2013 08:21 AM
If your building code will allow, I would suggest a duct free bathroom fan, NuTone makes one that can be installed in the bathroom ceiling or wall with no penetration to the outside. If you are installing a ducted AC, you could consider installing a supply vent in the bathroom and eliminate the fan. Another condsideration is to try and configure your interior layout with bathrooms on an outside wall to allow for installation of a small window, preferably in or near the shower.
50 cfm. minimum or 20 cfm continuous code no longer allow just a window |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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pcastleberg
New Member
Posts:13
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| 14 Mar 2013 11:58 AM |
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Very good point! Thanks! I would be more interested in just odor/moist air removal than anything so It could be anywhere, and if you do an over the range microwave you can get the ones that have the recirculating charcoal filter in it. That would help with odor's and catching the grease out of the air and would allow the HRV unit (in the ceiling..maybe over the center of the kitchen) to pull the moist air to be exchanged.
PS....how does a guy get spaces between paragraphs in this forum? I see that its possible but I don't see a way to do it. In every other forum I have posted in you just hit the enter key to create the line break and that does it. I don't see a way to do it here. |
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cmkavala
Veteran Member
Posts:4327
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| 14 Mar 2013 11:59 AM |
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Posted By pcastleberg on 14 Mar 2013 11:58 AM
Very good point! Thanks! I would be more interested in just odor/moist air removal than anything so It could be anywhere, and if you do an over the range microwave you can get the ones that have the recirculating charcoal filter in it. That would help with odor's and catching the grease out of the air and would allow the HRV unit (in the ceiling..maybe over the center of the kitchen) to pull the moist air to be exchanged.
PS....how does a guy get spaces between paragraphs in this forum? I see that its possible but I don't see a way to do it. In every other forum I have posted in you just hit the enter key to create the line break and that does it. I don't see a way to do it here.
it won' t post I will send in PM |
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| Chris Kavala<br>[email protected]<br>1-877-321-SIPS<br /> |
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Torben
Basic Member
Posts:216
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| 14 Mar 2013 01:10 PM |
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It appears to me you can still do an opening window in leiu of a fan/vent:
2012 Florida Residential Code
R303.3 Bathrooms.
Bathrooms, water closet compartments and other similar rooms shall be provided with aggregate glazing area in windows of not less than 3 square feet (0.3 m2), one-half of which must be openable. Exception: The glazed areas shall not be required where artificial light and a mechanical ventilation system are provided. The minimum ventilation rates shall be 50 cubic feet per minute (24 L/s) for intermittent ventilation or 20 cubic feet per minute (10 L/s) for continuous ventilation. Ventilation air from the space shall be exhausted directly to the outside.
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FBBP
Veteran Member
Posts:1215
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| 15 Mar 2013 11:07 AM |
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Joel - what heating system are you using?
Also be very careful of what those southerns are telling you ;-)) |
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Lbear
Veteran Member
Posts:2740
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| 16 Mar 2013 04:07 AM |
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The one drawback of the Aldes HRV is that the heat exchanger cannot be turned off. During a summer night when indoor temps might be around 80F and outdoor temps are 60F, one would like to bring in that cool outside air and remove the hot indoor air WITHOUT doing a heat exchange. It would be counter productive to temper the incoming outdoor air with the hot outgoing indoor air.
Are there HRV's which allow one to bypass the exchanger and just run it like a circulating fan? Removing the hot indoor air and bringing in the cool outdoor air during a summer night? I guess one could always just turn the unit off and open the windows.
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joeldunn21
New Member
Posts:23
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| 17 Mar 2013 12:35 AM |
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FBBP - I'm planning on a split geothermal system with radiant heat in the basement and forced air on the main & upper floors. |
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joeldunn21
New Member
Posts:23
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| 17 Mar 2013 02:04 AM |
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LBear
This HRV looks perfect. I think a half-ducted system putting fresh air into the HVAC while pulling stale air thru dedicated ducts in the bathrooms would work well. I see it only comes with 20 min timers. Any reason why you couldn't connect different timers with multiple times (10, 20, 30, etc) to this system?
Instead of a stand alone range vent hood, a microwave hood vent with charcoal filter and an HRV exhaust vent in another part of the kitchen may be another good option. |
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Lbear
Veteran Member
Posts:2740
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| 17 Mar 2013 07:02 AM |
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Posted By joeldunn21 on 17 Mar 2013 02:04 AM
LBear
This HRV looks perfect. I think a half-ducted system putting fresh air into the HVAC while pulling stale air thru dedicated ducts in the bathrooms would work well. I see it only comes with 20 min timers. Any reason why you couldn't connect different timers with multiple times (10, 20, 30, etc) to this system?
Instead of a stand alone range vent hood, a microwave hood vent with charcoal filter and an HRV exhaust vent in another part of the kitchen may be another good option.
All the experts agree that a fully dedicated ducted system for the HRV works best. Sharing the HRV duct work with the central air HVAC duct work never really works properly. One also has to run the air handler at all times which is more wasted money/electricity. These retrofits have been shown to be problematic. If this is a new build I would really try and run a fully dedicated duct system for the HRV. Each bathroom having its own exhaust duct and the kitchen having its own exhaust duct (6 feet away from the cooktop). The fresh air returns also having their own dedicated duct. You can install a charcoal grate option on the exhaust duct as on option they offer. The reasoning for the 20/40/60 timer is most likely due to preventing the unit from short cycling and premature breakdown. It's harder on the unit to constantly start and stop than it is if it runs continuously at slower speeds. |
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joeldunn21
New Member
Posts:23
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| 17 Mar 2013 08:58 PM |
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With air from the fresh air returns only being warmed by the HRV prior to entering the house won't this cause cool drafts where the fresh air returns are (especially in a northern climate like MN?).
Besides having to run the HVAC in order to use the HRV are there other drawbacks to ducting the fresh air returns into the HVAC and only having separate ducts for the exhaust ducts? |
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Lbear
Veteran Member
Posts:2740
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| 18 Mar 2013 01:12 AM |
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Posted By joeldunn21 on 17 Mar 2013 08:58 PM
With air from the fresh air returns only being warmed by the HRV prior to entering the house won't this cause cool drafts where the fresh air returns are (especially in a northern climate like MN?).
Besides having to run the HVAC in order to use the HRV are there other drawbacks to ducting the fresh air returns into the HVAC and only having separate ducts for the exhaust ducts?
That is correct. The fresh air returns during winter will blow cooler air and that is why returns should not be placed in areas where people might be sleeping/sitting. Place them up high and away from seating areas. The best HRV is around 90% efficient and so when it is 15F outside and 72F inside, the HRV can only condition the incoming air at 90% efficiency. There is an equation for this but I would state that the return air will blow around 61F. They also make a small heat resistant strip that can be turned on during really cold days and it is placed in the return duct. The colder it gets outside, the colder the return air will be. The other problems with using HVAC ducts is that it creates pressure imbalances within the home. You will either overpressure the home or create a negative pressure condition. The latter can cause a backdraft on certain combustion vents like a fireplace or furnace, this can result in carbon monoxide being funneled back into the home and the resulting DEATH of the occupants of the home. When you don't have a dedicated duct work for the HRV, you are never going to have a properly functioning system. Dedicated duct work creates a proper pressure balance, the same CFM of air going out and the same CFM of air coming in. Green Building Advisor experts do not recommend doing non-dedicated systems. |
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FBBP
Veteran Member
Posts:1215
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| 18 Mar 2013 01:16 PM |
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lbear - where do you get 61º supply air temp from?? If the exchanger core was working at 100% efficiency it could only raise the incoming air one degree for every degree it pulled out of the exhaust air so at BEST it would split the difference. So with 72ºf air going out and -30ºf (Joel indicates he is in western Mn, with out know the exact location, this is probably close to design temp.) air coming in the result would be closer to 21ºf. Certainly not something you would want dumping into living space.
The resistance heater that some HRV employ are usually defrost mechanisms and do not heat the incoming air. The unit you referenced appears to use indoor air for defrost. If there is a resistance heating module in any unit, it would require an breaker of upwards of 30 amps.
There is absolutely no reason a well designed HVAC unit would create any type of imbalance. If it is just heating the air in the house it will not effect the inside outside pressure at all unless it is still an open combustion unit. In that case the installer would need to bring in combustion air so it still would balance. If the fresh air side of the HRV was dumped into the return side of the f.a. furnace, it would still balance through out the house and would heat the incoming air as it passes over the furnace heat exchanger.
If the design temps are as low as I think they will be and Joel keeps the house anywhere above 35% r.h. then the core will be frozen for much of the time when outside temp approach this temp. Depending on the design of the hrv, it could simple slow down the exhaust rate or it could go into lockup and use electricity to defrost the core. not very efficient.
Joel - if you ARE using geo radiant for heat, you could use a small fan coil for dedicated make up air and just use straight exhaust. You will need to do some mechanical ventilation because you are going for a reasonably air tight house. While hrv's tend not to work real well in cold temps (this is why they become somewhat less common as the design temps drop,) they still provide some recovery in the shoulder seasons.
What is the reason for geo, if I may ask? Is natural gas not available in your area? |
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