Whole House Fans and High efficiency Furnace

[Annie-Laurie Hunter]

In a house with a whole house fan and a mid efficiency furnace there should be a lock out switch so the whole house fan can not operate when the furnace is operating.
Does the same rule apply with the high efficiency furnace with both an intake and exhaust to the outside?

Annie-Laurie

[Jerry Peck]

Annie-Laurie,

My guess is that there is also a gas water heater there too, right?

Whole-house exhaust fans are a bad idea anyway as they depressurize a house and draw moisture into the house. It will also draw in fumes from an attached garage or storage area where chemicals, fuels, mowers, cars, etc. are stored.

Having any gas appliance installed with a whole-house fan present is an even worse idea.

That said, I know of no requirement to have the whole-house fan shut off when a gas appliance is operating (thinking back to the gas water heater, gas range, etc.).

[Annie-Laurie Hunter]

There is a gas water heater, now that you mention it.

I suppose running the dishwasher and the whole house fan at the same time might not be a good idea.

Up here, whole house fans are great. You run them for 20 minutes at about 9 or 10 o'clock at night and the whole house is cooled down for the night in the summer.

Annie-Laurie

[Michael Thomas]

As a practical matter, it seems to me the degree of potential hazard would depend on whether the Cat IV appliance was drawing its combustion air from the exterior or the interior. If from the interior I would take the hazard very seriously - on a recent inspector I had a mid-efficiency furnace that was being back drafted by the WH fan so badly that I could not hold my hand 18" from the draft hood for more than a second or two.

[Annie-Laurie Hunter]

In this case the furnace was drawing the combustion air from outdoors.

[Jerry Peck]

In this case the furnace was drawing the combustion air from outdoors.

But was there a draft hood? If so, Michael was saying that the whole house fan created such a backdrafting that everything was coming out at the draft hood (at least, I think that is what he was saying).

If it is direct vent for combustion air and no natural drafting component to the vent, then a negative pressure on the space the appliance is in should not affect the appliance operation.

[Scott Patterson]

Annie-Laurie what is your location? Fill out your profile, it helps folks to answer questions sometimes.

Whole house fans were great when we did not have central HVAC systems, but just as K&T wiring worked well for many decades, it is old technology. When you combine new technology with old technology you usually run into problems. Look at K&T and when you add modern insulation, on top of it!

The same would go for a whole house fan. The owners either need to get rid of all old gas appliances and go 100% direct vent, 100% electric or get rid of the attic fan and install a central HVAC system, not just a furnace.

Do I report that attic fans can cause problems? Seldom, and most likely not enough.

[Annie-Laurie Hunter]

I filled out my profile. I am in Syracuse. Up here where it is snowing 5 months of the year, most people don't need to use an air conditioner more than 10 days a summer. And with the cost of running it, even more people don't want to.

Our night gets quite cool (60's) most of the summer so a few minutes to change the air before bed is about all it takes.

I have been writing up any whole house fans that don't have a safety lock out but it occured to me that if the furnace is high efficiency with the combustion air coming from outside and an induction blower if probably doesn't need it and I wouldn't want to put people through something they don't need to go through.


Annie-Laurie