HomeMy WebLinkAboutPermit Correspondence 2010-7-14
(J/O '778
To:
City of Springfield Building division
225 5th Street
Springfield, Or 97477
Attn: Steve Grahm
Inspector
Re: 2455 N 34th Street Residence Make up air for 900cfm max. range hood
Since the hood output exceeds the residential code max of 400cfm then the commercial code is applied.
The methodology is to take the total volume of air in the living space times the number of air changes
per hour divide that by 60 minutes to get an inflow cfm from natural and mechanical means. Subtract
from that any appliances that vent air from the building and the remainder is available to apply towards
the make up air. If the new appliance exceeds the current air available then additional make up must be
supplied.
In this residence there are no forced air inflow systems that operate year round, so only natural
infiltration will be used.
The house was built in 1967 so it is 43 years old. It is not built to any energy standards as required under
the new codes. Therefore it is very likely that the infiltration values are high. The construction is 2x4
walls w/insulation.
The house is electric heat (ceiling heat) there are no gas appliances other than a new residential range.
There are two bathroom fans rated at 35 cfm each a.nd an electric dryer rated at 150cfm. These are the
only venting appliances aside from the new hood. The total cfm outflow from these appliances is
290cfm.
A new energy efficient right home will average 2-5 air changes an hour. An older home may average
from 5-20+ air changes an hour.
If I use a conservative value of 6 air changes then 2000sf x 8' ceiling ht = 16,000 cf x 6 = 96,000/60
minutes= 1600cfm. 1600cfm - 290cfm (existing vent appliances)= 1310 cfm available.
1310cfm - 900cfm of new range hood= a balance of 410 cfm and requires no additional make up air.
If I went to 5 air changes 2000x8x5/60=1333cfm -290cfm=1043cfm. 1043cfm - 900cfm = 143cfm still no
makeup air required.
Less than 5 air changes would put this house in the class of a new energy efficient house and that would
not be an appropriate application.
Therefore I submit that using conservative values no make up air is required at this time.