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[2rjs]

I just recently bought a Legend 4135 furnace.  I have began the installiation but have some concerns about the size of the heat exchanger.  My house is 2500 sq ft and I only have room in my duct for either a 12x18 for 14x16 heat exchanger.  both of these are rated for about 90000 btu.  Will these be enough to heat my house?

Thanks,

[jerkash]

I asked the same question earlier.  Below is the link.

http://outdoorwoodfurnaceinfo.com/forum/index.php?topic=1137.0

I'm also in the process of getting a Legend 4135

[2rjs]

How many sq ft are you heating and what size did you end up going with?

Thanks

[Airgap]

If your original ductwork was sized properly when installed, and you have not added any more square footage the largest heat ex. you can fit, should heat your home.

[2rjs]

That's the problem!  My original duct work was sized for a 1800 sq ft house.  I added about 700 sq ft but I just extended the existing duct without giving much thought to it.  I've since had people tell me that the duct is too small.  My heat pump seems to do well now but it hasn't gotten cold yet.

[Airgap]

If it were me, I would get an HVAC contractor to come in and do some duct calculations. Especially since you've added that much sq. footage.

[willieG]

That's the problem!  My original duct work was sized for a 1800 sq ft house.  I added about 700 sq ft but I just extended the existing duct without giving much thought to it.  I've since had people tell me that the duct is too small.  My heat pump seems to do well now but it hasn't gotten cold yet.

im not sure what you mean by a heat pump? i have an in ground water furnace (besides my OWB) the way the heat pump (water furnace works) is it never gives hot air from the registers, it gives air that is about 7 to 10 degrees hotter than the room temp so having the heat exchanger int eh duct that is coming from the OWB giving off air that is 150 to 170 by far heats the home on the coldest day of the year. I would just fill your ductwork with a rad and see how she does. my heat pump has never kicked in but my rads fill a space of about 16x24

also your heat pump on the coldest day of the year will not be able to supply the same amount of btu as yoru stove on a continuous basis...fill with wood enjoy the heat

[willieG]

i guess what i really mean is 1-do you know what yor ductwork now is rated for (delivery of BTU per hour)

2- does your heat pump deliver  hot air in the real cold times of winter (some heat pumps as mine do not deliver hot air but warm air in high volumes)

an average 2500 square foot home needs (depending on your location) betwee 20 and 50 btu per hour per square foot so best case 2500 x 20=50,000 btu per hour max and worst 50x2500=125,000 per hour max.

take a look at this link

http://reviews.ebay.com/How-many-Btu-s-do-I-need-to-heat-my-home_W0QQugidZ10000000002054258

[2rjs]

I'm not really sure what btu it is sized for.  During really cold times the heat pump would delivery warm air but not hot.  However that was before I done the addition.

After I done the addition I seem to have good airflow to all areas of the house but I was concerned with the size of heat exchanger I could fit in which is only rated for about 90k btu.  Based on what you've told me, it sounds like I may be ok?

[mikenc]

You may look at getting coil with more rows. same size 12x18 but thicker.

[2rjs]

Yep, that's what I'd like to do if I could find one sized right.  I called Dodds Bros yesterday and they recomended a 4 row exchanger but they didn't have one to fit.  Anybody know of a place to get a 4 row 12x18 or 14x16?

[yoderheating]

 Be careful about using small thick heat exchangers, it may cut down on airflow. You would be much better off swelling your duct to 16 wide and using a 16x18 heat exchanger. It would most likely only take a hour or so and would get you good heat as well as good air flow.

[jdlieland]

I agree with WillieG, you fill that duct work with that size coil. Its going to be 5 times hotter than hotter than that heat pump air, Guaranteed.