Evaluating a Residential Ventilation System

It is interesting to me that the easiest steps in the process of settling on a ventilation system for a house are about all that the majority of programs follow: sizing the fans.  It’s not so easy to apply the standard to an actual house because you have to evaluate what is there now, is it ducted to the outside, can it be ducted to the outside, how much air is it moving,  does the homeowner really want to hood on the front of the house?  It is even complex to find the right products!  No wonder people just choose one and stick with it.  But there are a lot of ventilation product choices – unique solutions to fit unique situations.  Some solutions are more expensive than others, but meeting the ASHRAE 62.2 Standard may be as simple as increasing the size of the duct for an existing fan.

The steps involved in solving a residential ventilation situation are:

1. Size the whole building system: cfm = .01 x floor area + 7.5 x (bedrooms +1);
2. Size the local exhaust solution: 50 cfm intermittent bathroom, 100 cfm intermittent kitchen;
3. Select the design for the whole building system: exhaust-only, supply-only, balanced, balanced with heat or energy recovery;
4. Select a product that is quiet, has been tested to HVI specifications, and meets the airflow criteria;
5. Design an installation that will allow the system to work properly;
6. Install the system;
7. Test the installation;
8. Document the design details.

The fact is that the math is pretty simple. Selecting and installing and testing the system are not always simple. And the documentation is pretty straight forward. One of the simplest ways to clarify this is to do an analysis of your own house. Make an inventory of what you have for ventilation now, verify that the fans exhaust to the outside of the house, measure the flows, and document the system. You can use the TEC Exhaust Fan Flow Meter for most fans. You can use a duct tester.  You could use a vane or hot wire anemometer if you have one and do a traverse test.  If you have an HRV or ERV, you may be able to use the pressure taps on the unit to measure the flows and check the balance.  If it’s connected to the air handler, you should measure the pressures with the air handler running and not running.

ImagePHR talking about adjacent spaces

If your system runs intermittently, the total airflow should be enough to meet the formula in step 1 above. If the system runs half of every hour, for example, the flow should be twice the calculated rate. If it runs 20 minutes each hour, the flow should be 3 times the calculated rate. Then you have to verify that it really works that way. That’s a lot easier to do on your own system than when you’re verifying a system in someone else’s house.

There is definitely no point in going to the effort and expense of designing and installing a good ventilation system if the occupant is not going to use it. Mechanical ventilation gives us a license to tighten up the house as much as we want. It’s the ticket to tightening! The energy saved by tightening up the house can more than pay for the ventilation system.

(I want to thank the manufacturers that supplied me with products for my latest series of ventilation trainings: Broan for their Ultra fan, Panasonic for their WhisperGreen, AirKing for the ES80, Fantech for their SH704 HRV, AirCycler for their Smart Exhaust control, Honeywell for their HVC001 bath fan control, and Tamarack Technologies for their Airetrak Advantage.)

Paul Raymer – Heyoka Solutions, LLC


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