# Capacity needed for 2500 sq ft house

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• 06-18-2008, 11:29 PM
Quote:

Originally Posted by jrock52766
A load cal involves a lot of measuring and math. But a short run down is that the contractor will have to measure the square feet of all exterior walls, windows and doors. Est. the R value of wall and ceiling insulation and ACH(how loose/tight the home is). Then do a bunch of math with given factors for your area and ta-daa...now he will know how many btu's your house loses or gains according to avg. low temps. in winter and high temps. in summer. Then they can determine the size unit to suggest.

Jeez ! Are you talking about going to Mars !?! Neither guy did anything close to this !!!
They looked on the house, checked fournace and pump (kicking it...), asked for living area, said that new fournaces are smaller, so there is a steel bending work to do, said that they will work on it in home and call back ...
• 06-18-2008, 11:31 PM
RyanHughes
Quote:

Originally Posted by Montreal_Canada
Jeez ! Are you talking about going to Mars !?! Neither guy did anything close to this !!!
They looked on the house, checked fournace and pump (kicking it...), asked for living area, sayd that new fournaces are smaller, so there is a steel bending work to do, said that thei will work on it in home and call back ...

You're beginning to see that many companies do not do true Manual J load calculations--some don't know how, some don't see it as necessary, some are concerned with changing the size, etc...
• 06-18-2008, 11:42 PM
Quote:

Originally Posted by RyanHughes
You're beginning to see that many companies do not do true Manual J load calculations--some don't know how, some don't see it as necessary, some are concerned with changing the size, etc...

Yeah, apperently almost all of them are so pro, so they do not need any calculation.
Seriously, they say that for an average 2,500 sq ft house 90,000 BTUS are good enough, so well for a 3 ton pump ...
So is it a good idea to have two stage and/or variable fournace c/w heat pump ? Looking either for Carrier 25HPA5 and 58 MTB or MVT, or Lennox XP14 / XP15 c/w G51 (as I would not need 2-stage..) or G61 ....
Thanks a lot !
• 06-18-2008, 11:42 PM
beenthere
High efficiency equipment in a house that ins't well insulated is not a waste.
It would be nice for your heating and cooling bill if you could make improvements to youor homes weatherization.

With the proper thermostat, second stage will only come on when needed.
That may be 10&#176; colder then when the furnace took over, or less or more. Depends on the house.
• 06-19-2008, 12:03 AM
RyanHughes
I agree with beenthere. None of the furnaces you listed are variable-speed. I'd go with a variable-speed blower personally, for comfort and efficiency. Of course, properly-sized ductwork is necessary in any application to make a system work correctly (you mentioned that your old system worked well, though). For variable-speed furnaces, you'd be looking at Carrier's MVC, MVB or CVA (depending on efficiency) and Lennox's G60V, G61V or G71P (again depending on efficiency). A 2-stage variable-speed furnace wouldn't be a bad idea because as beenthere said there are some thermostats that can stage backup heat (I believe Honeywell's VisionPRO is one of them).
• 06-19-2008, 12:08 AM
Quote:

Originally Posted by RyanHughes
I agree with beenthere. None of the furnaces you listed are variable-speed. I'd go with a variable-speed blower personally, for comfort and efficiency. Of course, properly-sized ductwork is necessary in any application to make a system work correctly (you mentioned that your old system worked well, though). For variable-speed furnaces, you'd be looking at Carrier's MVC, MVB or CVA (depending on efficiency) and Lennox's G60V, G61V or G71P (again depending on efficiency). A 2-stage variable-speed furnace wouldn't be a bad idea because as beenthere said there are some thermostats that can stage backup heat (I believe Honeywell's VisionPRO is one of them).

Thanks ! Any thought for comparing these models Cerrier versus Lennox ?
• 06-19-2008, 12:14 AM
RyanHughes
Quote:

Originally Posted by Montreal_Canada
Thanks ! Any thought for comparing these models Cerrier versus Lennox ?

The better one is the one installed properly. Carrier's Infinity control system is nice, but it's not the only way to get good indoor comfort.
• 06-19-2008, 12:14 AM
beenthere
Ones as good as the other.
• 06-19-2008, 12:15 AM
Quote:

Originally Posted by RyanHughes
I agree with beenthere. None of the furnaces you listed are variable-speed. I'd go with a variable-speed blower personally, for comfort and efficiency. Of course, properly-sized ductwork is necessary in any application to make a system work correctly (you mentioned that your old system worked well, though). For variable-speed furnaces, you'd be looking at Carrier's MVC, MVB or CVA (depending on efficiency) and Lennox's G60V, G61V or G71P (again depending on efficiency). A 2-stage variable-speed furnace wouldn't be a bad idea because as beenthere said there are some thermostats that can stage backup heat (I believe Honeywell's VisionPRO is one of them).

On Lennox site I see some fournaces to be with "Low-speed fan — Provides a consistent, continuous flow of warm air" - is it as good as variable speed ?
• 06-19-2008, 12:24 AM
RyanHughes
Quote:

Originally Posted by Montreal_Canada
On Lennox site I see some fournaces to be with "Low-speed fan — Provides a consistent, continuous flow of warm air" - is it as good as variable speed ?

When I saw this a little while ago I was confused myself. I couldn't find anything in their engineering documentation that mentioned a low fan speed setting. Does any Lennox dealer know if this furnace has a low fan speed setting for constant fan?

Update: I just looked closer into Lennox's engineering data for the G60, and it says "Terminal for continuous low speed blower operation." There's your answer. Looks like these things can be setup for continuous low speed operation. I'm not sure what the "low speed" is, though. This is good for comfort; however, a multi-speed blower cannot vary its speed and isn't as efficient as an ECM variable-speed blower.
• 06-19-2008, 12:24 AM
Quote:

Originally Posted by RyanHughes
I agree with beenthere. None of the furnaces you listed are variable-speed. I'd go with a variable-speed blower personally, for comfort and efficiency. Of course, properly-sized ductwork is necessary in any application to make a system work correctly (you mentioned that your old system worked well, though). For variable-speed furnaces, you'd be looking at Carrier's MVC, MVB or CVA (depending on efficiency) and Lennox's G60V, G61V or G71P (again depending on efficiency). A 2-stage variable-speed furnace wouldn't be a bad idea because as beenthere said there are some thermostats that can stage backup heat (I believe Honeywell's VisionPRO is one of them).

When we talk for say MVB and CVA - there is a huge difference b/w 96 and 80 AFUE ... what is the price difference between them (as idea). And what about MVC ?. Thanks!!
• 06-19-2008, 12:31 AM
RyanHughes
Sorry, it's against site rules to discuss specific pricing--even rough ideas. And I'm not familiar with Carrier's pricing anyway. You'll have to ask your Carrier dealer. :)
• 06-19-2008, 12:34 AM