Thread: make up required?

Got a new construction home, electric water heater/HE furnace pulling intake from outside. No fresh air/make up air vent present. I know the mechanicals don't require it but what about when bath/kitchen vents are running. Thinking it would depressurize the home and cause little air movement due to how tight houses are these days. (no air exchanger) Any thoughts?

From the 2012 IRC: (bold and underlining are mine)
- R303.4 Mechanical ventilation. - - Where the air infiltration rate of a dwelling unit is less than 5 air changes per hour when tested with a blower door at a pressure of 0.2 inch w.c (50 Pa) in accordance with Section N1102.4.1.2, the dwelling unit shall be provided with whole-house mechanical ventilation in accordance with Section M1507.3.

- M1507.3 Whole-house mechanical ventilation system.
- - Whole-house mechanical ventilation systems shall be designed in accordance with Sections M1507.3.1 through M1507.3.3.
- - M1507.3.1 System design.
- - - The whole-house ventilation system shall consist of one or more supply or exhaust fans, or a combination of such, and associated ducts and controls. Local exhaust or supply fans are permitted to serve as such a system. Outdoor air ducts connected to the return side of an air handler shall be considered to provide supply ventilation.
- - M1507.3.2 System controls.
- - - The whole-house mechanical ventilation system shall be provided with controls that enable manual override.
- - M1507.3.3 Mechanical ventilation rate.
- - - The whole-house mechanical ventilation system shall provide outdoor air at a continuous rate of not less than that determined in accordance with Table M1507.3.3(1).
- - - - Exception: The whole-house mechanical ventilation system is permitted to operate intermittently where the system has controls that enable operation for not less than 25-percent of each 4-hour segment and the ventilation rate prescribed in Table M1507.3.3(1) is multiplied by the factor determined in accordance with Table M1507.3.3(2).
- - - - TABLE M1507.3.3(1) CONTINUOUS WHOLE-HOUSE MECHANICAL VENTILATION SYSTEM AIRFLOW RATE REQUIREMENTS
- - - - - (refer to the table for the requirements)


First and foremost, R303.4 means that a blower door test is REQUIRED (how else would one know what the air change rate was with a blower door test?) ...

... how many blower door tests are being done on houses built under the 2012 IRC?

It might behoove you to have a blower door test conducted to see just how tight the house is and if any make up air is being pulled in through seams, cracks, window frames, electrical outlets.

A heat recovery ventilator could be installed (HRV) and it would need to be sized and balanced.

Alternatively a duct from outside could be installed into the return air system.

https://www.cmhc-schl.gc.ca/publicat...ech/91-206.pdf

Or you could install a 6" dia. static make up air inlet as shown. The end of the duct is placed in a bucket and cold air is only pulled in when required. The bucket acts as a cold air trap.

Originally Posted by Raymond Wand

It might behoove you to have a blower door test conducted to see just how tight the house is and if any make up air is being pulled in through seams, cracks, window frames, electrical outlets.

A heat recovery ventilator could be installed (HRV) and it would need to be sized and balanced.

Alternatively a duct from outside could be installed into the return air system.

https://www.cmhc-schl.gc.ca/publicat...ech/91-206.pdf

Or you could install a 6" dia. static make up air inlet as shown. The end of the duct is placed in a bucket and cold air is only pulled in when required. The bucket acts as a cold air trap.

Thanks guys that will help. blower door test looks like only way to determine for sure.

As a new home built under the 2007 MN State Building Code, (2006 I codes, 2012 I codes don't go into effect until 1/24/2015) the code requires that the builder submit calculations to determine if, and how much, make-up air is required (2006 IMC Table 501.3.1). The local building department should have the information you need. Blower door tests are an option now; they will be required for all applications submitted after the 24th.