Replacing gas furnace, how big?

[Travelover]

Contractor #2 came and went and I must say that he spent a lot more time looking at the job and asking questions. Unfortunately, he also bases furnace size on square footage, though he did agree to take a sheet of data (dimensions, wall and ceiling construction) about my house back to the office and do a calculation.

Who ever put in the AC created a bumped out area on the furnace plenum to get the A coil in and he said the A coil needs to be reoriented to be correct. So that adds a little to the price, though he is also quoting a Lennox vs an Amana.

I think I'm convinced that I want to go with a two stage burner with a variable speed motor.

I appreciate the feedback from all of you.

[beenthere]

See what size his load calc says.

2 stage does improve comfort.

[ampulman]

I'm not a pro, but when watching the demonstration of HVAC-Calc heat gain/loss calculator, it suggested a 15-25% safety factor to add to the heat loss. Still, that's putting you at 40k btu.

Sizing by square footage is never the right way to do it.

Like Ryan, I'm also not a PRO, but did my own ManJ using HVAC-calc after several PROs gave 'varying' quotes.

The program doesn't assume any particular OD temperatures like in your case, but relies on you telling it where you live. The result is a more accurate 'starting point' at which to add any safety factor if you should so choose.

The OD (design temperatures) are rarely exceeded, so on very cold days, you will enjoy long heating cycles.

Amp

[rbeck]

The load calc's can be very accurate and uses the OD design temp in your area. Here is a chart for for the US.
http://www.comfort-calc.net/outdoor_design_temps.html

[BamaCool]

Most 2 stage equipment will work off of a single stage t'stat.Sure will, Take your pick, 1st stage or 2nd stage. I suggest that you call a couple of manufactures, ask who they consider is the best 3 dealers in your area and go from there.Yea, that'll work!

[ampulman]

The load calc's can be very accurate and uses the OD design temp in your area. Here is a chart for for the US.
http://www.comfort-calc.net/outdoor_design_temps.html

That's a neat chart. Is there a corresponding one for Summer time temps?

Amp

[hahnster1]

All due respects sir, just trying to point this customer in the right direction and be profesional. Yes , Carrier 2 stage equipment will work very well with a single stage t'stat, and the Infinity controls are even better but I shouldn't have to remind you of that. Oh by the way, having worked for 2 of the top 3 Carrier dealers in the St. Louis area, beleive me, the area distributors know who they can rely on! Why such the negative attitude?

[Travelover]

The load calc's can be very accurate and uses the OD design temp in your area. Here is a chart for for the US.
http://www.comfort-calc.net/outdoor_design_temps.html

The Manual J program I used has a similar city chart built in and it spit out a number within 1 degree of your chart.

[BamaCool]

All due respects sir, just trying to point this customer in the right direction and be profesional. Yes , Carrier 2 stage equipment will work very well with a single stage t'stat, and the Infinity controls are even better but I shouldn't have to remind you of that. Oh by the way, having worked for 2 of the top 3 Carrier dealers in the St. Louis area, beleive me, the area distributors know who they can rely on! Why such the negative attitude?

No negative attitude here, I just pointed out that not all 2 stage units will work as designed with a single stage t-stat. As far as the other comment about calling the manufacturer, if the HO asks for the "best" dealers they have, the only info they will get, if any, would be the ones that sell the most equipment, which by no means qualifies them as the best dealer for the HO, but rather, the best dealer for them.
That's all. No disrespect toward you either.

[ampulman]

The Manual J program I used has a similar city chart built in and it spit out a number within 1 degree of your chart.

What was the 5 degree assumed temperature you mentioned earlier?

Amp

[Travelover]

What was the 5 degree assumed temperature you mentioned earlier?

Amp

The Manual J I used assumed 5 degrees F outside temperature. The chart posted says 6 degrees F for Metro Detroit, thus 1 degree difference.

[ampulman]

The Manual J I used assumed 5 degrees F outside temperature. The chart posted says 6 degrees F for Metro Detroit, thus 1 degree difference.

O.K., I skimmed your original post....missed that. Sorry.

Amp

[Travelover]

In my original post I was lamenting that I only had 4 wires to my current thermostat and I'd really like to have a two stage thermostat (5 wires) installed, but running the additional wire would be tough.

I came across this Venstar Add-a-wire gadget. Has anyone used one? It seems like a perfect solution. Would a contractor carry this?

http://www.venstar.com/Support/Manua...ManualRev1.pdf