Furnace sizing and duct work

We just purchased a new to us post and beam house. The heating systems leave a lot ot be desired, The house has a 21 ft. cathedral ceiling, one 32 ft. wall that is almost 70% windows (triple pane). The house is fairly well insulated with 2 by6 walls. 1250 SF main floor, 700SF loft and 1250 SF basement ( insulated with 2 by 4 walls). There is also an attached 26 by 30 ft. garage. Part of the loft is cabover (over garage). The furnace is a 10 year old XL80 Trane mid efficiency. Presently the basement, garage and main floor also have in floor heat via a 40 gallon gas HW tank. One HVAC guy recommended that I do away with the HW tanks and install a 60 gallon electric for domestic HW and an electric boiler for the Hydronics. He also recommended a High efficiency furnace. This way there would be no chimney. We are located in the Canadian prairies and it does get very cold. According to the power company ( also the gas utility) there is not much cost difference in our area between gas and electric Hot Water. The duct work in th house is horrible. By the time the heat gets to the loft there is almost no force. I have not opened up the basement ceiling but I suspect too many bends. The previous owners had very high energy costs but they were very sloppy in their energy usage( 2 teens!)

Questions:

Are there tradesmen who or designers who can properly design a duct system?

Is 80,000 BTU enough furnace?

Can one use duct boosting fans?

What about a small furnace in the garage area with direct ducts to above?

Presently there is no central air and I doubt a system would cool the loft in it's present form.

With all the cu. ft. of air space and the high ceiling I dont think the floor heat will service the house without forced air assist.

Moisheh

troubles

It is near impossible for a designer to size the furnace andd cooling without a plan indicating local, materials of construction and orientation. If your furnace is standard eff. and the input BTUH is 80000 than the furnace is probably about 80% eff. with an output of 64000 BTUH.
Furnaces are notorious for not having enough external static capability to overcome the losses of the duct system so the designer has to pay particular attention to the duct size and layout.

Check with Trane and see if you can replace the furnace fan with a larger one also ask them about the feasibility of an inline fan in the supply duct. Check your breaker size or electric panel space to ensure that it can handle a larger fan motor or an additional inline blower.

In reference to cooling the loft area, I have never seen a "simple" system (one T-stat) that can maintain comfort in a lower or interior room and a second floor at the same time. The additional HVAC system for the area above the garage you mentioned has merritt

Your floorplan (cathedral ceiling, levels, cabover, etc) and issues sound very similar to mine when we first moved in, although we have a concrete slab, walkout basement and no floor heating. Our furnace is oversized by comparison with 110,000 Btu/hr input, standard efficiency and heats the whole home via 3/4 hp forced air.

The trick is in getting the heat where you need it to go. (Ditto for cooling with AC, but not an issue for you.) To get air out to the extremities of your system some of the other areas closer to the furnace will likely need to be closed/nearly closed. (You become a zone control.) It's not clear to me how your furnace is configured.

Manual balancing only helps so far though. Leaky and uninsulated ductwork will work against you. I spent a lot of time sealing all the duct joints I could reach, including at the plenum and air handler cabinet. Now a much greater percentage of the air actually reaches the end of the branches. Some of this is easy like sealing leaks at the register boxes. Others are difficult like reaching up into the main duct to seal gaps in branches between floors. I also insulated some exposed ductwork running through uninsulated space.

One thing to check in the cabover is whether or not there is insulation between the garage and floor above. Ours doesn't have any, and the long duct runs through the floor there are uninsulated as well. It is our master bedroom so eventually I'll address this deficiency. Fortunately, the garage is relatively well insulated and not too drafty, so losses are perhaps half of what they would be if this was an external wall. It's going to be a major PITA to fix as I'll have to completely remove the textured drywall ceiling in the garage.

I'm guessing that on the Canadian prairie you are getting super cheap hydro electric. If your electric came from elsewhere then natural gas would likely whip it hands down for water heating.

p.s. The previous owners of this home used three times as much electric annually as we do...and they did that with half as many occupants.

Get a HVAC engineer ASAP

Unfortunately such disasters are common. You really need a HVAC consulting engineer who can run the numbers. Some years ago I built a multi level house with the lower bedroom level on slab.

The heating contractor (by his own admission a "tin knocker") installed 2 hot air furnaces, a 60K BTU 92% condensing for the lower level BR wing and a 120K BTU 92% condensing for the remainder Total SF was about 2,700. Troubles began at once. The 120K unit was serious overkill and had temperature overshoot because of this. This meant that there was excessive temp swing in the upstairs. Not a comfortable situation. The lower level with the 60K was a disaster. The 12 inch round duct was buried in the slab without sufficient insulation surrounding it and had way too many bends. As a result the bathroom and far BR just didn't get sufficient heat, the flow was low and the air was tepid.

After adding a couple of in duct booster fans (noisy suckers!) with limited results I finally gave up and called a HVAC consulting engineer. He came, made lots of measurements and basically ran off without a solution. (He never billed me either). I did some more patch fixes but never did solve the problem entirely.

Lessons learned: 1. Get a competent HVAC guy in as soon as possible. 2. Patch up measures rarely do the job unless they are part of a well thought out plan. 3. Beware a contractor who solves his incompetence by putting the largest unit he can buy ---- too big is just as bad as too small!

Sorry for the long winded post.

Thanks for the great replies. I will take all the advice to heart. I think it may be time for a little "detective" work.

Moisheh