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# Need advise in regards to Gas Furance

#1
04-23-17, 01:27 PM
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Need advise in regards to Gas Furance

I am looking to help my dad change his heating system from a coal-fueled system to a gas (propane) furnace. I have been measuring of all the rooms in the house (2 story)

I may have did the calculation wrong, but I measured each room ( length width height ); for example my living room is ( width=15ft / length=23ft / height=9ft ); then I multiply the three to get the total sq foot, I repeated this for each room & then added them all together to get my total sq footage that is being heated.

So that gave me a total of 21,747 sq feet does this seem right ? All suggestions & feedback to help me get this off the ground would be awesome!

#2
04-23-17, 01:38 PM
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Square footage is length x width only. 23'x15' = 345 sq feet.
Volume is L x W x H.

#3
04-23-17, 01:55 PM
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Ok, when I do L x H x W would be my air volume that I would need which is for duct sizing I am assuming for (CFM); so I did make a mistake it was 24x15 the living room.

So here is what I get L x W = 360 sq feet. So when I multiply 24x15x9 I get 3240 so I am assuming the measurement are different sq foot vs air volume correct?

So I will re-calculate all my measurement to get my total sq footage to be heated correct? just LxW ?

#4
04-23-17, 02:22 PM
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Joshua, you don't need to know the volume for a load calculation, just sq ft.

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04-23-17, 03:27 PM
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Awesome, so I just re-measured all my L x H of each room & then added them all up, I have around 2,365 Sq feet!

So now that I got the sq feet down for each room that will need heat. Next is find the proper size furnace I'll need, I found a size calculator & inputed my sq feet that will need heated including my zip code as it very's due to cilmate, so I rounded my number from 2,365 to 2,400 & than it showed me I'd need a 62 BTU so I am assuming this would be 62BTU/hr.

Does this seem correct to you'll & any suggestions on furnace types? I been scoping out a Goodman gas furnace they are priced just right & warranty seems good! So suggestions?

EDIT: I seem to have made a mistake it 2,400 __NOT__ 24,000

Last edited by joshua_; 04-23-17 at 05:49 PM.
#6
04-24-17, 07:34 AM
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Any advice on the size of unit I would need with the sq footage of the house?

#7
04-24-17, 10:07 AM
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Replacing a heating system is not a diy project. neither is designing one unless you know the theory.

Duct sizing done right is never done on the basis on square or cubic feet.

only a room by room load calculation.

And after that point it hinges on btu's per cfm, equivalent duct lengths, and other factors.

If this old house has a old gravity style duct system, it all needs to be ripped out and new perimeter supplies put in. The old supplies on exterior walls can be used as returns with new trunk lines.

You need a skilled designer who has connections sheet metal and hvac contractors.

Most contractors do not receive the training to properly engineer a system; they get licensed to repair and install. They may know some theory, some may be better than others.

It's going to be very expensive to do right. prices will vary depending on area, but if you get things done right i think it won't be lower than 10 grand, and probably closer to 15 or even higher.

And it would be wise to reduce heat loss of the house before changing the heating system. The BTU output requirements of old houses with no insulation can be cut by 30 to 50%+.

Some houses, like those that have framed walls will be easier and more worth while to retrofit.

#8
04-24-17, 10:13 AM
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for calculations, it's the exposed surface area times temperature difference divided by net thermal resistance value of each material that counts.

sq footage goes up to the square of surface area.

#9
04-24-17, 03:01 PM
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Thanks to everyone who has commented/suggested on here thus far.

@Muggle: I appreciate your comments here, & I am sure you are right on all of this, now in regards to what I have done thus far, I have made messasurements of each room in two different ways, one in volume & one in just sq feet. I just totalled the sq feet to help size the unit itself ONLY at this point. Once I have concluded the proper size then I will start basing the duct size from there, by simply as you pointed out & I agree w/ is load calculation for each room & then size the duct from there weather it be a 6' 8' or so forth.

So my main objective here is to come up w/ the proper size gas furance for this house, again no cooling needed only heating is my primary concern at this point.

#10
04-24-17, 07:23 PM
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ignore the user name, tried to get it changed.

to determine the heat loss, your best best is measuring the whole exterior of the house.

and the height of each floor.

check insulation, check wall construction type. you can sometimes tell by removing an outlet plate and probing with a long tooth pick.

2x4 or double brick, insulated vs not if framed?

try something like this, if u can enter figures manually ->https://www.coolcalc.com/products/manual-j

i really think you should consult a designer. i would if it was my own project.

The design of ductwork and installation of the furnace itself i would sub out.

if you're handy and good with metal, you may be able to manage removing the old coal system and running ducts if u can get the sheet metal fabbed.

Sheet metal is hard to deal with unless you're a pro, but at least there's no latent safety hazard. (though you will get lots of nasty cuts! that stuff is super sharp where cut.)

This is truly a huge project.

#11
04-24-17, 07:40 PM
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You'll need to start with the proper load calculations

Manual J for heat loss
Manual S for equipment selection
Manual D for duct design

You'll also need to pull all the required permits from the local code enforcement especially for the gas piping.

#12
05-11-17, 07:48 PM
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1. You will need experienced installers to put the unit in, and to design the PROPER ductwork with correct sizing. If you do this yourself, it will be done very badly and the house will have various comfort issues (or worse). Sorry but it is very clear from the back and forth and your questions that this is the case. Some people might be able to design and do it themselves. You are just not one of them - no offense meant. Figure on \$3000-6000 to install the heater and ductwork.

2. Simple sizing is just SQ FT * 25. So, yeah a 60,000 BTU furnace is fine, regardless of a standard or high efficiency unit. Essentially, on a really cold day you want it to run nearly all the time to keep up with the heat loss. What you don't want is a unit that will keep cycling on and off every 10 min. That's bad! A large unit would do so. That's the easy part.

Figure out whether it's worth the extra expense for the high efficiency vs a standard 80% efficiency unit. There MIGHT be tax advantages that would compensate for the extra expense for a high efficiency unit. The actual energy savings between a 80% and 95+ unit is minimal and the ROI is usually so long without tax incentives that it's usually not worth it.

3. What a gentleman mentioned about SEALING THE HOUSE is very very on point. It is super critical to finding and sealing all penetrations between the attic and the top floor. Very often the ceiling fans, attic doors and ceiling recessed lights are letting out TONS of heat. Use caulk and low expansion (yellow) foam to seal up all of that (and weather stripping for the attic door). Make it all TIGHT.

Second to that are other leaky areas (often around doors and windows hidden behind trim pieces.

Check the attic to see if it has a really nice heavy layer of insulation - WITHOUT GAPS. In WV you'll want LOTS of it.

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