[carlom]

Hi everyone,

I am going to buy a new Heat Pump + Furnace and have spoken to several contractors. The problem I'm having is with getting consensus on the right size for my home. There are a few contractors that recommend a 3.0 T system and others recommend a 3.5 T system. I did the J Load calc using the online calculator and was hoping for some assistance. I may have misunderstood some of the parameter inputs. Please see attachment.

I have a 2 story cottage style + basement. 2250 square feet (without including the 1100 sq ft basement). I live in Southern Quebec (Montreal region).

Looking at a Trane XL15i + TAM7 furnace. Leaning towards 3.5 T but worried about oversizing the system.

Let me know your thoughts.

Thanks

 

[snupytcb]

for some reason I can't open the manj results. what does it calculate for heat loss and gain? 3.5 sounds a little big (comparably) but is too hard to sy from here. how well is the structure insulated? hhow about infiltration? have there been any recent upgrades? money is best spent when improving te buildings envelope. how old it the home?

 

[carlom]

The calculation seems highly dependant on the CFM fresh air. If I leave the field blank, the results are as follows:

Total Btu's Cooling 27493
Sensible Load 25910
Latent Load 1583
Total Btu's Heating 109755

If I input 450 CFM fresh air, the results are:

Total Btu's Cooling 39409
Sensible Load 29870
Latent Load 9539
Total Btu's Heating 147870

To answer your questions:

1.) House built in 1999 according to local codes. Nothing above code.
2.) Infiltration should be relatively minor.
3.) Only upgrade is finishing the basement but that had minor insulation impact.

 

[snupytcb]

100k btu seems high, that's a lot of heat and not common to install anymore. It seems like something may be amiss with the calc. I can't be sure but it isn't what we see often for that size house. you may want to look into doing a manual s and d as well. what do you have now and how does it perform?

 

[carlom]

I currently have the following combo:

Ruud Heat Pump: 3.0T Achiever (This was a warrenty replacement. I am 75% sure the original was a 3.5T)
Ruud Furnace: UBEH-21J18SUNA (Can you tell me if this is a 3.0 or 3.5T unit?)

In summer, unit works A LOT when it's hot an humid. I can't say we're uncomfortable however. Overall, it did the job.

The contractors are willing to sell the 3.0T or 3.5T units are the same price so I'm not worried about saving $$ on the equipment. It's more a concern around proper functioning and humidity control.

 

[beenthere]

You want the A/C to work a lot when its hot and humid outside.

 

[snupytcb]

I am not a ruud/rheem guy so I don't know the size. I did try to find it but no luck other than it is an electric furnace. I the 3 ton existing system did alright then i recommend tightening up the house a bit and definitely evaluate the ductwork. your current system may be lacking the airflow and if corrected then 3 ton would work. plus, if you do bump up to 3.5 you should be sure the ductwork will handle that. most of the time we see undersized/ poorly designed ductwork when doing estimates.

 

[lkapigian]

The calculation seems highly dependant on the CFM fresh air. If I leave the field blank, the results are as follows:

Total Btu's Cooling 27493
Sensible Load 25910
Latent Load 1583
Total Btu's Heating 109755

If I input 450 CFM fresh air, the results are:

Total Btu's Cooling 39409
Sensible Load 29870
Latent Load 9539
Total Btu's Heating 147870

To answer your questions:

1.) House built in 1999 according to local codes. Nothing above code.
2.) Infiltration should be relatively minor.
3.) Only upgrade is finishing the basement but that had minor insulation impact.

Seems high for fresh air...but I'm not in Canada 3 cfm per 100 square 7.5 cfm per person...Teddy Bear may be along......would love to see your inputs, I'm betting you are more in the 3 ton range

 

[carlom]

Let me know if you can see the jpeg of the j load calc.

http://www.mediafire.com/view/3shohpg3hb1a00b/j_load.jpg

 

[BadgerBoiler MN]

This load is not likely.

Your contractor should perform a Manual 'J' and produce the results with explanation. Ask them for a factory verification, the local supplier can help them out.