Cold air return placement in hearth room.

[lumbajac]

I originally had the following post in the boiler room, but think it might fit better here in the hearth room...

I am planning on using an RSF Opel3 zero-clearance fireplace along with a natural gas forced air system to heat my new home. I plan on burning the fireplace 24/7 for the entire heating season and would like the natural gas to kick in as little as possible. The fireplace will be located in the living room of the first floor... home will be a two story with full basement.

The RSF Opel3 has an optional central heating kit that can tie in directly to the central heating system’s ductwork. See pg. 21 of the RSF online brochure if unfamiliar with this… brochure can be found at: http://www.icc-rsf.com/c/icc/file_db/maindocs_e/RSF-CAT.pdf. I visited a dealer this past week and got a good look at the stove. I am definitely going with the RSF Opel3, but am leary about spending the $500 plus for the central heating kit if I can find a better way to distribute heat, plus another $200 or so on other items that would be needed for this setup to work.

Instead of the optional central heating kit I am considering their gravity heat kit, which would allow air to naturally flow below the fire place unit itself through a louver, behind the fireplace and up, then out 2 separate gravity vents either on the front or on the sides of the fireplace… I’d then have a cold air return near each of the two gravity vents at ceiling level to capture a lot of this heat… having the variable speed fan on the natural gas furnace running very low all the time, on a timer to cycle on every so often, or on a thermostat to kick on when a certain temperature is reached would then distribute this heat to the whole house through the natural gas furnace’s central heating ductwork. I’m thinking this option would save hundreds of dollars up front on optional kits, would rely less on potentially noisy add-on blowers, and would probably consume far less power given that the new variable speed blowers on natural gas furnaces draw very little power as compared to what I would expect an add-on blower from the fireplace manufacturer to consume. If not familiar with the setup I am speaking of, woodheat.org has a good article with a diagram related to this type of heat distribution at: http://www.woodheat.org/planning/heatdist.htm

Any thoughts on this setup would be much appreciated.

Thanks,
lumbajac

 

[Redox]

I am probably going to get read the riot act for saying this here, but I have much of the return from both our central systems right next to the stove. It keeps the family room from overheating and spreads the heat out to the rest of the house, where it will do some good. I have the downstairs furnace on a timer to run the fan on low during the night. The upstairs system only runs when it is very cold and the return is preheated by the stove. It works very well. I know the return is supposed to be 10 feet from the stove, but I have never heard why.

That being said, I agree with you that it isn't a good idea to connect the fireplace directly to the furnace return as the heat can cause problems with the furnace itself.. My 90% furnace specifically states that you cannot have a return above 85F as there will not be enough cool air to condense the flue gasses. The furnace would just shut down on thermal overload. The fan motor in your furnace is cooled by the return air and most motors are rated for a 104F maximum ambient anyway. If you have one of the new ECM (variable speed) motors in your furnace, you will be using less current on low than most stove or fireplace fans draw. Most of the small blowers I've seen use a shaded pole motor that really isn't very efficient.

Just because I do it, doesn't make it right, though...

Chris

 

[lumbajac]

I am probably going to get read the riot act for saying this here, but I have much of the return from both our central systems right next to the stove. It keeps the family room from overheating and spreads the heat out to the rest of the house, where it will do some good. I have the downstairs furnace on a timer to run the fan on low during the night. The upstairs system only runs when it is very cold and the return is preheated by the stove. It works very well. I know the return is supposed to be 10 feet from the stove, but I have never heard why.

That being said, I agree with you that it isn't a good idea to connect the fireplace directly to the furnace return as the heat can cause problems with the furnace itself.. My 90% furnace specifically states that you cannot have a return above 85F as there will not be enough cool air to condense the flue gasses. The furnace would just shut down on thermal overload. The fan motor in your furnace is cooled by the return air and most motors are rated for a 104F maximum ambient anyway. If you have one of the new ECM (variable speed) motors in your furnace, you will be using less current on low than most stove or fireplace fans draw. Most of the small blowers I've seen use a shaded pole motor that really isn't very efficient.

Just because I do it, doesn't make it right, though...

Chris

Good info... I wasn't aware there was a 10' required distance from the fireplace to the cold air return, but it makes sense to not overheat your furnace or the blower itself. I'll look into this.

Thanks,
lumbajac

 

[quinn]

Lumbajac

I have an old home that has been fully insulated and updated so it is reasonably well insulated. With the woodstove in the living room on the main floor the house was too cold upstairs and in the rooms at the opposite end of the house on the main floor. I put in two cold air returns at ceiling height in the room with the fireplace and found that it moved some of the hot air. The living room did not get as hot when the furnace was running and hot air was being sucked out and distributed. However, I did notice a significant improvement in the colder rooms in the house. Too much heat from the cold air returns was lost as the wood heated air moved from the living room through the ducting to the rest of the house.

What I have done now is to remove the wall above the doors to the coolest parts of the house and voila, heat is moving beautifully. With this change I am heating a 2700 sq. foot house without any fans (other than ceiling) or using the furnace fan. If your house is very well insulated and if you insulate the ducting that carries the wood heated air I think your plan will work. If however, your ducting is not insulated I think you will find that most of your heat is lost as the air travels from one room to the next, particularly if that ducting passes through a cold basement.

 

[lumbajac]

Lumbajac

I have an old home that has been fully insulated and updated so it is reasonably well insulated. With the woodstove in the living room on the main floor the house was too cold upstairs and in the rooms at the opposite end of the house on the main floor. I put in two cold air returns at ceiling height in the room with the fireplace and found that it moved some of the hot air. The living room did not get as hot when the furnace was running and hot air was being sucked out and distributed. However, I did notice a significant improvement in the colder rooms in the house. Too much heat from the cold air returns was lost as the wood heated air moved from the living room through the ducting to the rest of the house.

What I have done now is to remove the wall above the doors to the coolest parts of the house and voila, heat is moving beautifully. With this change I am heating a 2700 sq. foot house without any fans (other than ceiling) or using the furnace fan. If your house is very well insulated and if you insulate the ducting that carries the wood heated air I think your plan will work. If however, your ducting is not insulated I think you will find that most of your heat is lost as the air travels from one room to the next, particularly if that ducting passes through a cold basement.

Thanks - if I go with this setup, I will definitely insulate the cold air returns from the fireplace room back to the furnace.

Anyone have thoughts on whether the central heating kit would be a better option and worth the $500+ for the materials?

-lumbajac