Question from energy homeowner:

 

Contractor has recommended installing a two stage Water Furnace Envision w/desup NDV049A system into a 2700 square foot cape cod, 1000 square feet basement, 1000 square feet first floor, and a 700 square foot second floor.  The house is all brick and was built in 1950, walls and attics are currently insulated using r 11.  The blower door test gave a  2800 cfm reading at 50.

 

Contractor is recommending a 4 ton geothermal system, According to his comments it is a two stage system that  will run at 60% capacity at the first stage and 100% at the second stage.  Contractor feels the 4 ton system will provide more heat using the geothermal without going to the back up heat.,

 

If the system is over-sized to accommodate the heating season, does this make sense.?  He says with a two stage system it does.  Will the system operate efficiently.  If we were installing a regular electric heat pump the manual J test called for a 3 ton system  (single stage)   Is the contractor correct in over-sizing the unit to provide more geothermal heat in the winter months?

 

One other question: What is the advantage of using galvanized ducts as compared to 1 inch rigid fiberboard ducts?

 

Thank you for responses

 

 

 

Views: 779

Reply to This

Replies to This Discussion

Hi my name is Steve.

If the manual J suggested a 3 ton I would look at a 3 ton two-stage. The two stage units are usually a 1/2 ton larger in size. When I size my units, I try to shoot for a balance point of 5 to 10 degrees outside temperatures here in Michigan. The operating cost seems to be the best at these temps (even with the little back up thats needed). The reason is the larger compressors use most electricity. Now, it's not a lot of difference in operating cost. Having the next size larger is not devastating but you need to have larger duct system and extra loop installed driving up installation cost.

My question is? Did the contractor you are referring to complete a manual J load and does he know where his balance points are. If he can not show you he calculations he is guessing and not doing you a good job.

Note: The home generates a certain amount of heat and you can design at 77% of the calculated load. So if the manual J says you can install a 3 ton then it does not matter if it it two stage or not. Sorry I have to go now my wife i waiting, You can contact me if you have more questions at performancegeothermal@gmail.com.

Steve Shannon

PS, I like sheet metal for duct work.

If the contractor doesn't calculate a manual J,D, and S worksheet for the house then he's merely guessing. Also, galvanized ducting last much longer, is easier to clean, and is more rigid that fiberboard.

RSS

Home Energy Pros

Home Energy Pros was founded by the developers of Home Energy Saver Pro (sponsored by the U.S. Department of Energy,) and brought to you in partnership with Home Energy magazine.  Home Energy Pros is sponsored by the Better Buildings Residential Network.

Latest Activity

Profile IconJohn Doe and Ariston C. Hernandez Jr. joined Home Energy Pros
12 hours ago
tedkidd replied to Damien Greenfield's discussion Is there is cost saving for you in having a tankless water heater?
"Bob, here is where our perspectives diverge. I think people should switch to electric because they…"
yesterday
tedkidd replied to Damien Greenfield's discussion Is there is cost saving for you in having a tankless water heater?
"Here our thinking falls out of alignment. Going to electric is default for me. People can't…"
yesterday
Bob Blanchette replied to Damien Greenfield's discussion Is there is cost saving for you in having a tankless water heater?
"If you are going to stay with gas service, might as well keep the gas water heater. Switching gas…"
yesterday
tedkidd replied to Damien Greenfield's discussion Is there is cost saving for you in having a tankless water heater?
"8 people, sometimes under 10 therms. Just not enough energy used heating water to get obsessive…"
yesterday
Eric Kjelshus replied to Damien Greenfield's discussion Is there is cost saving for you in having a tankless water heater?
"Biggest is to keep the CO  or other gas down in building  "
yesterday
Bob Blanchette replied to Damien Greenfield's discussion Is there is cost saving for you in having a tankless water heater?
"Look at your SUMMER gas bill where water heating accounts for most of your gas use. 10-15 therms…"
yesterday
Bob Blanchette replied to Damien Greenfield's discussion Is there is cost saving for you in having a tankless water heater?
"The marathon fails miserably in operating costs when compared to an ordinary gas water heater.. NG…"
yesterday

© 2015   Created by Lawrence Berkeley National Laboratory.

Badges  |  Report an Issue  |  Terms of Service