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becktheeng

How many btu's for direct vent?

becktheeng
15 years ago

I'm trying to minimize the size of a new direct vent fireplace in a living room (approximately 15'x20'). I live in So. Cal and would use the fireplace to warm the living room (east facing) as it seems that the furnace does not do an adequate job to keep the room comfortable. We'd like to use the room more often and thought that building a direct vent with built in cabinetry may be just what we need. Is there a formula for btu/sq foot?

Thanks!

Comments (9)

  • fandlil
    15 years ago

    I think some manufacturers of direct vent products (and other heating products) give estimates of how many btus you need to heat so many square feet. Most direct vent systems will heat an "average size room" whatever that is. The challenge is to distribute the heat througout the room instead of it being concentrated only near the unit. Most come with built-in blowers, which can be noisy on high speed, but are reasonably quiet at slow speed. An alternative is a ceiling fan that can be reversed so that it blows up toward the ceiling instead of down from the ceiling. That reverse air movement can be accomplished by a fan motor that can turn the blades in the opposite direction from the one you use in summer or, a fan with blades than can be "twisted" so that they can move air up instead of down. Since a direct bvent system is sealed, you can use a ceiling fan to accomplish this. But you cvannot do that with a traditional fireplace because the fan's air movement would conflict with the chimney's updraft.

  • becktheeng
    Original Author
    15 years ago

    Thanks...I'm considering putting a fan in the living room anyway as the ceiling is vaulted and I thought that a fan or large light fixture would help to "bring the ceiling down".

  • sniffdog
    15 years ago

    Look at getting a fireplace (I presume it will be gas?) that has an external thermostat control (I like the hand held remote kind), a blower fan, and a flame adjustment. Then you can tailor the output of the fireplace to room temp and seasonal variations automatically. You coul dtry doing a manual J calculation just for that room to determine the BTU's per hour needed, but that type of analysis is normally done for sizing HVAC systems and is based on worst cases.

    If you really want that manual J - post on the HVAC forum and tell them the size of the room (LxWxH), the type of walls and insulation, the size and type of windows, the typical external temp, the normal room temp, and how much warmer you want the room to be. They should be able to help.

    I have a Fireplace Xtrodinare FPX 864 TRV gas fireplace with a hand held remote. I use this unit to provide backup heat as well as ambience in my library which is 15' x 33' x 22 foot ceiling. It has a low flame flow valve so that I can turn the heat down during normal operation (6700 BTU output). When I need backup heat, I turn the valve and can generate up to 31000 BTU's. The handheld remote is placed in the room where we want to achieve a desired temp. Then the fireplace will turn the internal blower fan on and off based on the temp reading at the remote. It works great. The blower fan and hand held remote were accessories. There are also smaller capacity units available with similiar features - the unit I have is probably overkill for what you need, but it looks great in a big room.

  • becktheeng
    Original Author
    15 years ago

    Thanks sniffdog....I like the idea of an external thermostat. Did that feature add much cost to your unit?

  • sniffdog
    15 years ago

    The blower fan was $125 and the hand held remote was $130. I did not view that as expensive. These accessories were made by the fireplace manufacturer.

    Perhaps second party units might cost more but I found the FPX pricing for the extras to be reasonable. The fireplace was not cheap (Actually - expensive) - but they did not try to rip me on the add ons.

    I would check the other brands to see what they offer. Since I use my unit as a backup heat source (and I live in an area where it gets cold in winter) - I paid the money for the best quality heater rated fireplace I could get. For ambience and a little blast of heat, you might not need to spend as much.

    Good luck.

  • christopherh
    15 years ago

    How cold does it get where you live? Right now here in VT it's minus 10 outside. It's going up to 20 today and my stove is just chugging away.

  • sniffdog
    15 years ago

    I live in the Blueridge Mtns in Northern VA at about 1200 feet elevation. This morning it was in the high teens, low 20's. With winds (10 to 30 mph typical) its very cold.

  • fandlil
    15 years ago

    I'm in Chapel Hill North Carolina. The heating systems in this region generally work fine when the temp is down to the low 30s. But when it drops to the 20s, the furnace really struggles to satisfy the thermostat setting. That's considered "normal" here, because it doesn't get that cold very often. Therefore, builders are reluctant to install larger furnaces to deal with the colder weather, which is rare. I suppose it's about the same in Virginia, or perhaps not in the mountains.