Thread: Furnace Capacity

The 2 yrs old 6,100 sf 2-story with finished basement detached house having a high efficiency Lennox 110,000BTU input installed. The living room has a high ceiling. I told the client HI do not do the heat balance calculation but I thought this furnance heat capacity is at the margin. This could be the reason the home has 3 fireplaces installed. The client hired a heating service guy who said the furnace is brand name & good enough for this house, which I doubt.

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Originally Posted by Peter Louis

The 2 yrs old 6,100 sf 2-story with finished basement detached house having a high efficiency Lennox 110,000BTU input installed. The living room has a high ceiling. I told the client HI do not do the heat balance calculation but I thought this furnance heat capacity is at the margin. This could be the reason the home has 3 fireplaces installed. The client hired a heating service guy who said the furnace is brand name & good enough for this house, which I doubt.

A house like that in my area would most likely have 3 independent HVAC systems. One for the basement, one for the main floor and one for upstairs.

Originally Posted by Scott Patterson

A house like that in my area would most likely have 3 independent HVAC systems. One for the basement, one for the main floor and one for upstairs.

I agree or at least two.
If the house is super energy efficient, maybe........ For your own information, if you know a good HVAC tech, call him/her up and run this by them.

Unless the Seller can provide documentation for high level insulation and sealing, I'd say its nonsense. 6000 sqft is way beyond the capacity of one 110K furnace. Normally you'd be looking at 2500-3200 sqft under ideal conditions.
Around here that house would have 2-3 systems.
Its not only a questions of unit capacity but also airflow. I don't see how you'd get any air to the far areas of the house. Even a booster fan is installed then you'd have to account for temperature drop. It's all nonsense.

Without a heat loss calculation you are guessing.
Nothing about insulation levels either, so defer for further investigation by HVAC tech.

What is a Load Analysis and Why Is It Important?
It is a detailed calculation of how much heat is gained or lost by your
home under a specific set of conditions. It includes such things as the
size of each room, the size of windows, type of windows, size of door
and their type, insulation levels, and magnetic orientation of the home, temperature highs and lows for geographic area.

What Other Methods of Sizing Can Be Used?
There are no alternatives to doing a room-by-room Manual ‘J’ load
analysis. Developed by the Air Conditioning Contractor‘s Association
(ACCA). Manual ‘J’ is the only method approved by all equipment
manufacturers as well as the Department of Energy and the EPA. It is also likely required by the building department of your jurisdiction.

Most companies won’t spend the time or make the investment in
education to learn how to do a Manual ‘J’ calculation. Because this is
a voluntary procedure, most companies will cut the corner and guess
at the actual size of equipment and ducts needed for the job.

What Is the Result If A Manual ‘J’ Isn’t Performed?
Without the information resulting from a Manual ‘J’ calculation, there
is no accurate way to determine the size of equipment needed, the
size of ducts needed, the number and size of supply and return
outlets in each room and ultimately can and does lead to over or
under sized systems, noisy systems, imbalances (hot and cold spots)
in the system and higher operating costs. In short, the company that
fails to do a Manual ‘J’ calculation is just guessing at the size and
numbers of all the components needed to make your home
comfortable.

for that big window & high ceiling I prefer mini 120K output about 125K input though our winter is normally mild.

When you were there did you operate the furnace? Did it reach temp and shut off or run for hours on end. This will tell you if it's heating the house at least. I would think it's small for that size of house but the house could have R-30 in the walls for all I know. Much more info would be needed to even give a decent guess.

No info on whether the system is zoned, multi staged.

I’ll chime in on this subject since it has been a while . ..

I didn’t catch where the home is located but for the sake ofthis argument I will assume it is in a milder area of BC, say Spring Islandwhich has a winter design temp of 29°F, downright balmy by some standards.

A 110,000 BTUH highefficiency furnace would produce about 100,000 btu’s of heat which comes out toabout 17 btu/sq foot, which for a well-insulated home with good windows is notout of the question of being adequate. If I chose to live in a 6,000 SF home Iwould certainly want more than that, ifnothing more than for better zoning, but I still think it is workable.

The one thing that really blows it all out of whack is thethree fireplaces. IF they are nottightly sealed boxes that pull 100% of their combustion from outside there isno way in HE dbl toothpicks that furnace will be adequate. The chimney effect on a flue would pull so much cold air in that the heating requirement could easily tripple. The largest loss onany home or building is infiltration and that is one of the more difficultthings to predict.