Installing gas fireplace to supplement forced air - input needed!

peace_roseNovember 3, 2011

I need help choosing the right sort of gas fireplace to install/build in our basement addition to supplement the heat in the rest of our house. Here's the details:

Seven years ago we installed a new 60,000 BTU furnace (80% efficient) in our 850 sf ranch home (we also use the entire 850 sf in the basement). In the meantime we've added a 350 sf addition, as well as an additional 350 sf basement addition. (We cut a hole in the original foundation and added on below grade). So we now have 1200 feet above grade and 1200 feet below grade that needs to be heated, and the furnace isn't big enough to accommodate it all. We've investigated and have learned we would need a 75K BTU furnace to do the job. We've ruled out electric baseboard heating (too expensive in the long run to operate) and upgrading the furnace (seems like a waste to remove a perfectly good furnace. And running ductwork to the new addition would be tricky, too)

This is where installing a gas fireplace seems like a good option. The south wall of the basement addition (15' x 23') runs along the exterior of the house and could be easily vented to the outside. It also sits right underneath the gas line to the kitchen stove. We're thinking that we would run it on chilly days, and it would passively heat the new addition above it. Just enough to take the chill off. The basement walls are currently unfinished and the ceiling joists are still exposed, too. The plan is to insulate it all once it's drywalled, etc, but being unfinished gives us some leeway right now.

My husband has the expertise to do all the venting, wiring, gas, carpentry and tile for the mantle, and would be doing it on a homeowner's permit. (He's not just an average DIY guy - he really IS skilled). But we do need direction on what SIZE of fireplace to install, and any particular things that would be helpful to know. Also, will this considerably add to our heating bill if we go this route?

The house is brick, built in 1945, but has many upgrades (new windows, insulation, etc). Located in Denver, CO, where many winter days are in the 50's, but temps often drop below 30 degrees. Lastly, the room will be used either as a master bedroom or a family room, so people will be sleeping there. Aesthetically it's the perfect spot for a cozy fireplace!

Thanks so much!

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PS - Forgot to mention that it's Natural Gas (Xcel Energy). NOT propane.

    Bookmark   November 3, 2011 at 1:19PM
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Hi, Rose: I would say that you are underestimating how cold Denver is. The number of degree days there is about 6,000. If you live in the foothills that could easily go up to 7000--8000. I would guess that 10 degrees F is a good design temperature for Denver. The design temperature is the coldest temperature that you are likely to hit several times a winter.

Even so, 60,000 BTU is not necessarily too little heat production. In your shoes I would be asking if I have a heating deficit or a distribution problem?

The heat load for a house your size-- even with the basement-- in Denver should be well under 60,000 BTU if it is well insulated. The first thing I would do is check my insulation and then do or have done a heat load calculation. You may not need any more furnace at all. However you may need new insulation and new ducting. If you do want to get an insert, I recommend those made by Travis industries. (I own two of them and love them). They will be higher efficiency than your current should be plenty.


    Bookmark   November 3, 2011 at 7:17PM
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Thanks, Will. Ten degrees several times during the winter sounds about right. Sometimes I forget just how cold it gets here. We are in the city itself. I keep the thermostat around 68 degrees. On a cold day outside when it's 68 in the front of the house, it's about 63 in the back (ie, the new addition).

Thank you for framing it in terms of heat deficit vs. distribution. The ducts are basically vented to the front half of the house; partly because two were taken offline in the process of building the addition. And partly because it's awkward to run them to the furthest part of the new addition without getting in the way. (Thus the reason why we're in this predicament of considering a fireplace). We had a blower door test done - house is circulating 30% of its air each hour. And we did have a heat load calculation done - that's how we arrived at the 75K figure. But it would be great if the current furnace could handle the whole load. So all of this is to say, I'm still curious to know what size fireplace we might install. I'm guessing it wouldn't have to be very big. Anyone want to estimate what we would need?

    Bookmark   November 4, 2011 at 1:00AM
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