UGHH!!!My builder put in closed cell sprayed insultation along with our two  wood burning fireplaces in our one level 3000 sqr foot house. The way the Heat Pump is pulling air through the system/ filters through the returns, it seems that the house is very, very  tight.
When we light one or both of these fireplaces where will it pull air in from? Are we going to suffocate because the fireplace wants air yet the house is so tight it will use up all the oxygen?

You should ask the builder to explain how the fireplaces are vented and where the combustion air comes from.

What kind of fireplaces are they?

It takes more than just close-cell insulation to make the place tight enough to preclude running a fireplace, but assuming it IS that tight it's not too tough to run backdrafting test and know for sure.

Even where there are problems, the problem isn't going to be using up all the oxygen, but rather putting toxic combustion products into the indoor air- you'll die of carbon monoxide poisoning LONG before you run out of oxygen in the room, so don't sweat it! ;-)

Turn on all of the kitchen & bath exhaust vents, AND the air handler AND the clothes dryer, then check the fireplace to see if you have a nice steady flow of air coming down the flue when you open the damper. If yes, some remediation may be in order.

If you don't already have one, if the house is that tight you really need an ERV or HRV ventilator to keep indoor air quality up. Most of those would provide sufficient combustion air for a fireplace, even though running the fireplace would temporarily put the ventilation balance out of whack from the lower pressure induced by the fireplace.

The two fireplaces are Heatalator Icon Series 60- 36-Inch Woodburning Fireplace and Icon Series 80 - 40-Inch Woodburning Fireplace.

I think I will try Dana1's suggestion by turning on the Kitchen Exhaust, two Bathroom Exausts, Air Handle,r and the Dryer and then open the damper. If I understand your idea Dana1, I then would open the damper and see if the flow of air in the fireplace is being pulled back into the house which would then mean I need to somehow get better airflow into the house.
Should I open only one of the fireplace dampers or both of them? I'll use a small bird feather to see which way the air ends up flowing.

I hope the feather does throughthe roof and not back through the house.


Thanks

I assume this is with small fires burning - if not, I would expect any house to pull air down the chimney when you have other exhausts running. I'd like to think that builders could be more precise about it and actually measure infiltration and pressures and get everything balanced (on a room by room basis if you have ducts) - but I doubt it.

You should get the optional outside air kit for those fireplaces.

Considering this and other issues, can someone explain how open fireplaces are considered "green"?

I agree with ICFHybrid that open fireplaces are not useful in a high energy efficiency house. The best way to keep open fireplaces from backdrafting is to open a nearby window and then let your air heated by your conventional heater go up the chimney. I have a sealed combustion system, natural-gas fueled, fireplace, which means that it brings in outside air for combustion air. It provides some ambience and is reasonably energy efficient. If you like fireplaces, and want to have an energy efficient house, this is one approach.

I have also stuffed a wood-burning stove into a fireplace to get net heat delivered to the house (a previous house) instead of sucking it out. This works fine and heated the whole house, but it can often be a fire hazard if not done carefully, and a neighbor burned down his house with this approach. Further, the ambience is gone unless you use a glass-fronted firebox.

There are EPA certified fireplaces or wood stoves, whatever you want to call them, that are sealed, have glass fronts and are extremely efficient wood burners. They use outside combustion air while delivering the heat to the inside of the building.

I agree on the wood stove comments. They are far better for energy efficiency than an open fireplace. A fireplace really has no place in the design of a new house that is proposed as being energy efficient, as they tend to leak air badly, need far more combustion air for proper draft than a stove, and don't lend themselves easily to using outside air ducted in for the purpose.

For our new (superinsulated and very tight) house we finally moved into a couple of months ago, I selected a Quadrafire Millenium 2100 wood stove. It was the smallest they make, has a tight welded steel firebox, glass front door, and an adapter for attaching an outside air duct. We actually heated the whole house with it over last winter, before the heat pump was installed and made operable. I don't worry about drafts around the stove when it isn't burning, since the air/stove/chimney loop is completely sealed off from the living space air. I looked at a small Vermont Castings stove, but it didn't have the outside air duct capability; the stove shop phoned the vendor to verify that, and was told that such a duct would just dump air "into the vicinity of the stove," a poor solution in my mind. An outside air duct shouldn't be allowed to dump raw air into the living space, unused for combustion, when the fire is dying out and the stove is producing little heat. With the duct connected directly to the stove, any air flowing in through the duct just goes right back out the chimney, so heat loss is minimal.