Thread: Open circulation floor registers

A recent discussion on a woodheat group is about cutting air vents through floors to allow heat to circulate in single family residences. The general scenario is a wood burning stove in the basement and the owner wanting more heat to go upstairs. So if the owner cuts a hole in the floor lines it with tin and puts a floor register on it with it being open to the basement area where the stove is; is it legal, illegal under (Which?) code. Does distance from the wood stove matter? Thanks for your input.
Gary from Wisconsin.

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Originally Posted by Gary Goetz

A recent discussion on a woodheat group is about cutting air vents through floors to allow heat to circulate in single family residences. The general scenario is a wood burning stove in the basement and the owner wanting more heat to go upstairs. So if the owner cuts a hole in the floor lines it with tin and puts a floor register on it with it being open to the basement area where the stove is; is it legal, illegal under (Which?) code. Does distance from the wood stove matter? Thanks for your input.
Gary from Wisconsin.

Gary,

I don't have a code for you, but I cannot imagine why it wouldn't be ok. Stairways are essentially a hole in the floor system as are laundry chutes. However, I would not vouch for any efficiency.

Most municipalities, building codes and fire departments refrain from permitting cutting holes because of smoke and fire spread.

Cutting holes in floors in order to help distribute the heat are not effective, and I have never seen any that actually allow the heat up.

I can't vouch for the efficiency, but there's no code issue. You can have as many openings in a floor as you want.

Firestopping only applies to concealed openings (such as holes in plates within a wall cavity).

As Gunnar said, a stairway is just a large hole in the floor. There's no need to firestop that.

Commercial constuction is dfferent. Required egress stairs have to be enclosed, and floor/ceiling assemblies usually have a fire rating, which prevents unprotected openings.

Originally Posted by Gary Goetz

A recent discussion on a woodheat group is about cutting air vents through floors to allow heat to circulate in single family residences. The general scenario is a wood burning stove in the basement and the owner wanting more heat to go upstairs. So if the owner cuts a hole in the floor lines it with tin and puts a floor register on it with it being open to the basement area where the stove is; is it legal, illegal under (Which?) code. Does distance from the wood stove matter? Thanks for your input.
Gary from Wisconsin.

That would basically make the basement into a supply plenum, with all exposed items in that supply plenum, i.e., an 'under-floor plenum' basically.

Normally, "under-floor plenums" are meant to cover the crawlspace area, not a basement, but, making the basement into a plenum means it would need to meet the same requirements (for the same reasons).

From the 2006 IRC.

- M1601.4 Under-floor plenums.

An under-floor space used as a supply plenum shall conform to the requirements of this section. Fuel gas lines and plumbing waste cleanouts shall not be located within the space.

- - M1601.4.1 General.

The space shall be cleaned of loose combustible materials and scrap, and shall be tightly enclosed. The ground surface of the space shall be covered with a moisture barrier having a minimum thickness of 4 mils (0.1 mm).

- - M1601.4.2 Materials.

The under-floor space, including the sidewall insulation, shall be formed by materials having flame-spread ratings not greater than 200 when tested in accordance with ASTM E 84.

- - M1601.4.3 Furnace connections.

A duct shall extend from the furnace supply outlet to not less than 6 inches (152 mm) below the combustible framing. This duct shall comply with the provisions of Section M1601.1. A noncombustible receptacle shall be installed below any floor opening into the plenum in accordance with the following requirements:
- - - 1. The receptacle shall be securely suspended from the floor members and shall not be more than 18 inches (457 mm) below the floor opening.
- - - 2. The area of the receptacle shall extend 3 inches (76 mm) beyond the opening on all sides.
- - - 3. The perimeter of the receptacle shall have a vertical lip at least 1 inch (25 mm) high at the open sides.

- - M1601.4.4 Access.

Access to an under-floor plenum shall be provided through an opening in the floor with minimum dimensions of 18 inches by 24 inches (457 mm by 610 mm).

- - M1601.4.5 Furnace controls.

The furnace shall be equipped with an automatic control that will start the air-circulating fan when the air in the furnace bonnet reaches a temperature not higher than 150°F (66°C). The furnace shall additionally be equipped with an approved automatic control that limits the outlet air temperature to 200°F (93°C).

Gary,
Also being from WI. I see this as common to 70 and 80 yr. old 2 story homes, but not anything newer. I can't say they can not do it (it's their home) but it seems bubba-ish and although it may serve the purpose there are better ways to do this. They do have grates on the floor and on the ceiling (usually), and I have seen these ceiling grates about to fall off. That could smart from a 9' ceiling, not to mention other debris falling through the grates. Does'nt sound safe or very smart to me. Howd's you write it up?

Jim Weyenberg
HouseMaster Inc.
Green Bay and Fox Valley WI.

On the other foot if you have Kids down in the basement you can put your ear to the registers and find out there next move!

Always good to be one step in front of the gang

Best

Ron

Here is some more info on why people want holes in their floors. We are talking about died in the wool woodheat folks here. I haven't fired off my gas furnace in 2 years except to see if it still works. Many of us prefer systems that use no power at all. Many feel that the best set up is the wood burner in the main living area for several reasons. Generally the efficiency is highest that way. It's nice to be able to watch the fire. It is a shorter trip to adjust and refill the stove resulting in better operating practices. Less wood burned, less smoke, more even heat. Anyway some members have wood stoves in the basement for many reasons (think spouse) or existing chimney - wood access. So anyway if the wood heater is in the basement moving the heat up with out electricity really needs floor vents (big ones) Thanks for the input so far. Keep the cards and letters coming. I am not an inspector just spent years in the home building industry trenches and generally interested in as built vs code issues and attitudes.

Vents closest to the wood stove would likely work the best, while vents further away will do nothing as cold air falling will negate the warm air rising through the vents. Remember cold air is heavy and dense.

I would also recommend that if you take this course of action, even though many codes won't allow it to install smoke and CO detectors in each room which will have a floor vent.

Most wood heat members believe both close and far vents are needed to set up a circulation. An open basement stairway door often serves as the far vent. I have both a living room stove and a basement stove, the living room unit sees the most use but the basement stove gets run spring and fall for slower heat up cool down cycle and every few days in really cold weather to warm floors and basement plumbing pipes.
My living room unit is a sealed combustor equiped fireplace enclosed in a masonry stack with floor and ceiling air circulation vents. It produces even heat without the use of the fan. The stack weighs about 3/4 ton and helps even out the heating cycle. The master bedroom is 5 steps up from the living room and the temperature there is perfect for us. I burn about 5 or 6 cords of wood to heat about 1600' in Wisconsin. My house is a 60's trilevel that I have completely renovated, new windows, doors, 1 /1/2 foam under new siding 15" fiberglass in ceilings etc.

Well logic would say that the heat will rise. Logic would also say that the heated air will need to be forced through an opening. Why? Well if you have cold air that is pushing down on the heated air, the cold air will win. If you cut a hole in the floor the cold air will just keep sinking down that hole and will keep the heated air from rising up through the hole. So unless you can create some form of draft or air movement I don't see it working.

You might try posting this on The Inspetors Journal This is another home inspector BB and I think a few folks on it are wood burners.

Scott,

I can see it working where the openings closest to being above the wood burning stove will send hot air rising and the further away opening will be where the cooled air settles back down to the basement.

Think of it as a duct-less gravity system. Very inefficient, but they work.

You should consider the dwelling itself before attempting to install floor vents. If the dwelling has good air exchange (lots of leaks) then you are less likely to cause injury. If the dwelling was built following some form of energy codes or if there has been new windows, doors, flooring, roofing, kitchen hood, HVAC system, or if your natural draft fireplace barely meets the sizing requirements, then you may be creating a hazardous condition. Positive, natural and negative pressures within your dwelling may be affected when adding any openings through the floor line.

The stairwell is often the cause of malfunction due to its location in the floor plan and its distance from any natural draft appliance (example; fireplaces, water heaters and boilers). An increase in negative pressure can be created by the stacking or movement of heated air in an upward direction. If the lower dwelling areas air supply can not be replenished at the same rate then the negative pressures will increase. This probability can be increased when natural draft systems compete for the same air as the mechanical draft appliances. The end result may be a malfunction in an appliance and injury or death to the occupants.

This type of modification is simple and cheap. It has been my experience that simple and cheap usually equals malfunctions and injury.

Having lived in a 1849 Grist Mill with a woodstove located in the great room with bedrooms above on the 2nd floor and with 2 floor vents installed in the bedroom I can tell you that the floor vents (bedroom directly over the woodstove) did nothing to keep the 2nd floor bedroom warm. As a matter of fact in the winter months it was common to see ice forming on the inside panes of the windows, not frost but ice! The floor vents were both approximately 18" square. The vents served no purpose whatsoever. I was far better putting an oil filled electric heater in the room.

Allot of the older homes in Baltimore when I was growing up had gravity oil furnaces. They where located in the floor of the hallway and close as possible to the 2nd floor stairs. All the rooms had grates in the floor open to the first floor. Never heard anyone complain and one friend of mine still has one in his 50's built home. He said there was temperature difference between the rooms on the 2nd floor and it was much cooler then the first floor which was toasty but he could live with it.