heat loss 1

[marcus4127]

I have a house with an existing undergrond galvanized duct system under a concete slab. We used a company called Enviro Dust seal to spray a thin (1-2 mils.)rubberized duct coating made by enviroliner to coat the the duct, so we would have a clean and sealed duct system. After installing a new Bryant High efficient hvac system, It is producing 125 degree air at the plenum and 105 degree air at the register closest to the unit. As the air travels through the duct, by the time it gets to the other end of the house we have only 70-75 degree air coming out of the registers. The system is a 5 ton unit that runs for 2-3 hours and only heats the house to 65 degrees. Is that much heat loss normal?
Any help or Ideas how to fix this issue would be greatly appreciated.

 

[MiketheEngineer]

Is this a heat pump??

 

[marcus4127]

It is a split system with a gas fired heat exchanger

 

[dvd]

Has the system been balanced? Correct airflow in (and out of) each room? No excessive air leaks?

You might eventually transfer enough heat into the fill material that the heat loss from the duct is minimal (for winter usage with the opposite true for summer). Operating over time the system will be at steady-state. What does your HVAC contractor have to say about the problem?

Eventually, I would start considering insulated duct installed in the attic.

 

[marcus4127]

The system has not been balanced yet going to try that next, but there is so much heat loss. By operating the system Over time how would that correct the problem?
There is no attic it is a two story house with new insulated duct for the upsairs unit that is working fine
hvac contractor has no solution

 

[chicopee]

It seems that you lack adequate insulation.

 

[IRstuff]

Did it ever work? Can you confirm that the flow rate is correct? Are you sure there's no bottleneck?

Is it in contact with the soil? Soil, particularly if it's wet, makes for a poor insulator. How cold is the soil? A brute force calculation of convective heat loss says that 100ft of 10" diam pipe would sink about 2 tons of your heating capacity.

TTFN

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[willard3]

The forum rules discourage DIY projects.
Hire a contractor or an Engineer

 

[marcus4127]

I understand that we lack insulation, but you would think that the original system would have worked at one time.
The soil was dry around the elbowes, so I do not think the ground is wet.