Ventilation. Residential Low Rise

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1 Ventilation Residential Low Rise As of January 1, 2010, the 2008 California Building Efficiency Standards requires mechanical ventilation for Residential units. All new low rise dwelling units 1 and existing low rise residential buildings with additions over 1000sft 2 now have to meet the requirements of ANSI/ASHRAE Standard Ventilation And Acceptable Indoor Air Quality In Low Rise Residential Buildings (ASHRAE 62.2 ). ASHRAE 62.2 allows for window operation in certain climate zones 3 to meet this standard, however that exception does not apply in California. The California Energy Commission specifically states Window operation is not a permissible method of providing whole building ventilation required in section 4 of that standard 4 Bath fans are required in all baths even if there is a window. A kitchen fan is also required. For smaller homes bath and kitchen fans can meet all the whole house ventilation requirements. Larger homes will need a combination of local exhaust and whole house ventilation or your existing forced air system can be modified to meet the requirements. The ventilation requirements can be met either using intermittent or continuous fans. The advantage of using continuous ventilation is that smaller equipment is needed. To determine the required continuous ventilation rate you can use the following table: Ventilation requirements in Cubic feet per minute Floor area Bedrooms (ft²) > > Example: What ventilation rate would you need for a 1200 sft house with 2 bedrooms? Using the table above, you would need 45 cubic feet per minute (cfm). Or you can use the following formula for a more precise value: =1200/ (2+1) = =34.5 cfm 1 Subchapter 7 Section150(o) 2008 Building Efficiency Standards for Residential and Nonresidential Buildings 2 Subchapter 9 Section152(a)Exception Building Efficiency Standards for Residential and Nonresidential Buildings Exception.a ANSI/ASHRAE Standard Subchapter 7 Section150(o) 2008 Building Efficiency Standards for Residential and Nonresidential Buildings

2 Rounding up, you would need fan rated for continuous duty capable of providing 35 cfm. By using the formula rather than the table, you can meet the ventilation requirements by putting in a smaller fan, so don t be afraid of doing the math. How much intermittent ventilation would you need? You can also provide intermittent ventilation controlled by a timer that operates the ventilation system no less than one hour in twelve, in other words, twice a day. You can calculate the intermittent ventilation rate by using the following formula and table 5 : = intermittent fan flow rate = required continuous ventilation rate =ventilation effectiveness (from table) =functional on time (%) Ventilation effectiveness for intermittent fans Daily functional on time- Ventilation effectiveness- 35% % < 60% % < 80% % 1.00 For the same example used before, that is a 1200 sqft house with 2 bedrooms, we already determined that for continuous ventilation 35 cfm ( would be needed. So if we wanted to operate the fan 30% ( ) of the time which would be 72 minutes every 4 hours, using the table we come up with.33 ( ) ventilation effectiveness. = 353 cfm.. An intermittent fan for the same house running 30% of the time would need to be capable of ventilating at 353 cfm. Infiltration credit: For older homes, if you have had a blower door test showing that you have a leakage rate over 2 cfm per 100sft of living space, you can reduce the amount of required ventilation. The amount of reduction would be half the amount of infiltration measured above and beyond the 2cfm per 100sft default level. What equipment do you need? Negative pressure systems, exhaust only: As mentioned, bath fans are required. The minimum size and table 4.2ANSI/ASHRAE Standard

3 required for a bathroom is 25 cfm 6 if run continuously or 50 cfm if it is operated by a switch. Continuous bath fans must be sound rated at 1 sone. Intermittent fans must be sound rated at no more the 3 sones unless they are rated for more than 400cfm. The fan manufacturer will also have sizing requirements that also must be followed. Kitchen fans whether a ceiling exhaust fan or a kitchen range hood are also required. For continuous use, a minimum of 5 air changes per hour (ach) of the kitchen area is needed. Say your kitchen is 12 by 14 with a 10 ceiling. You would need an exhaust fan capable of providing a continuous 140 cfm. (12 x14 x10 x 5 ach) /60. For intermittent use, a range hood providing 100 cfm would be the minimum size fan needed. If your 1200 sft 2 bedroom house had a bath fan that was 1 sone and rated for continuous duty at 35 cfm, and a 100 cfm intermittent kitchen rage hood, you would meet the requirement at least for the mechanical side. Although this is the least expensive and easiest method to meet the requirement equipment wise, it may not improve your air quality if the sources of replacement air are coming from crawlspaces or garages or attics. When you use a negative pressure method of ventilation such as this, it must be in combination with sealing off undesirable sources of replacement air. 7 Most old Berkeley homes have no air barriers between the crawl space and the living space. The floors are predominantly 1x6 fir subfloor, covered by a finished oak floor. When there is a negative pressure in the living space above this type of floor, as much as 60% of the replacement air can come from the crawl space. If there is an attached garage, ducts terminating originating or passing through the garage must be sealed. Drywall edges and walls in the garage must be sealed. Positive pressure systems: If you would prefer to chose the source of the air coming back into the house, you might want to pressurize the house. You can have a fresh air ventilation system installed on the return side of your existing forced air furnace. The air coming into your furnace is required to have a screened inlet ten feet away from any possible source of contamination such as other exhaust ducts. The intake must also be filtered to at least MERV 6. The watt draw of this type of system must be less than 0.58w/cfm. If a default value of 0.8w/cfm is used as a design performance approach value, no HERS verification of watt draw is needed. The Fan On switch may be used for continuous operation or a timer must be used for intermittent use. It is important to note that by pressurizing the dwelling you could be increasing heat loss in the winter by exfiltration through cracks and gaps in the building. This could also increase the amount of moisture inside the wall surfaces. Balanced System: A Heat Recovery Ventilator balances the air coming in with the amount of air going out and recovers heat from the exiting air to warm the air coming in. Though this is a more expensive system, however it creates fewer problems as air is neither forced out, nor pulled in through the leaks in the building. Once again, the air coming into your HRV is required to have a screened inlet away from any possible source of contamination such as other exhaust ducts and be filtered to at least MERV 6. 6 ASHRAE 62.2 requires 20 cfm, California code requires 25 cfm minimum ANSI/ASHRAE Standard

4 Switching: Continuous systems need to be installed to operate without occupant intervention, but the override must be readily accessible. Any switches controlling a required ventilation system need to be labeled as to function unless it is obvious such as a bath fan switch. Owner s manual: Installation and operation instructions shall be provided to the owner and occupant. Ducting: 3 flex duct is not permitted. No more than 5 feet of 3 smooth duct for fans up to 50cfm is allowable. 4 flex duct can be used for 70 feet for up to 50cfm fans, 35ft for 80cfm fans, not permitted Additional Information: 2008 Building Efficiency Standards Compliance Manual and look at section 4.6.

5 Equipment Image Means Pros cons $ Continuous local fan bath (neg Inexpensive Cannot identify or control quality of replacement air, heat loss due to infiltration Continuous local fan kitchen (negative Outside air input to heating system (positive switching measures with existing fans ( negative Relatively inexpensive Filtered air from known source, Low cost, when using existing appropriately rated fans Cannot identify or control quality of replacement air heat loss due to infiltration More complex, system must meet energy use, heat loss increased due to infiltration to out of doors heat loss due to exfiltration $ Cannot identify or control quality of replacement air, heat loss due to infiltration plus install <100 Heat recovery ventilator (HRV) Balanced Energy recovery ventilator (ERV) Filtered air from known source, recovered heat from out-going air, balance system, not relying on infiltration Energy recovery though moisture exchange. Useful in areas with high cooling loads. $$$$Expensive $$$$$Expensive not suited for this climate zone 1300 plus install 1500 plus install Whole house fan

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