Poor performance from new Propane Furnace - please help

Old 02-07-14, 10:46 AM
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Poor performance from new Propane Furnace - please help

We recently built a new house last summer here in League City, Texas (near Houston). We have 6" walls with R-19 blown cellulose insulation. I don't even know what is in the attic, but I estimate it is around R-50 because it is a 22" double layer of fiberglass and cellulose (long story). The house is a 1.5 story, 3500 total, 2700 down, 800 up. The upstairs is just playspace and theater room, no bedrooms - so we rarely run HVAC up there. The downstairs has a lot of windows, but they are mostly covered with blinds and are all double pane Low E-SC. ceilings are 9 and 10 ft throughout downstairs. Before insulating I spent a month with 4 cases of caulk and 3 cases of spray foam sealing EVERY joint and air leak possible. It is tight.

BUT, our heater performance is terrible. It takes so long to heat the house, and we are always cold. We have to keep it at 72-73 just to be marginally comfortable with sweaters on. Last night it took 55 minutes to raise the air temp a single degree. We keep it at 66 during the day, and when we set it to 71 when we return that can take over two hours.

The furnace is a Trane 4 ton XT80 that is converted to propane. It is only 6 months old now. Pressure of the propane is verified at 11 in-H2O. The outlet temp at most of the vents is around 110-112deg, but some of them are around 102-105. The thermostat is a Radio Thermostat (similar to the 3M models) that is controlled by my alarm system. It controls to within .5 degree. I have verified its accuracy with a secondary thermometer. Ductwork is exposed in the attic and is R-8 insulated. We have return air ducts in all of the bedrooms.

For reference the upstairs unit is a 2 ton XT80. It gets hot really quick, but it should since it is 2 tons on only 800 sq ft. I think it was sized this way more for the AC and rising heat in summer than for the heater. The ACs are Trane XR15s. They seem to work okay, but I have not been through a super hot summer yet.

I really think that the main problem is lack of air flow. There is so little air coming out of any given vent. It is more than a wisp, but it is not impressive at all. It is not enough to feel that it is even on unless I get up on a ladder and hold my hand to it. The HVAC company is giving me the runaround saying that it needs to be balanced. But they expect me to do it. I do not thing that is the problem however, because no vents are getting excessive flow and no rooms are excessively hot or different temperature.

I would like to know if anyone has any thoughts on what could be the problem? Could it be that the heater is under sized? Is it a blower problem? A leak? I really really wish I had not installed a propane heater. It is costing us a fortune to keep this tank full, and it is really not that cold here (30s and 40s at night).

Any help or ideas is appreciated. Are there any tests that can be done to measure CFM of air from all the ducts to add up the total air and see if it is all there?

I have attached our ductwork schematic.

Thank you so much.
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Old 02-07-14, 03:06 PM
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air flow

before going to the individual rooms you need to check at the furnace. you need to check the nameplate data and then check the temperature rise at the furnace. if it syas 40-70 degree temp rise,you check the return air temperture,you then check the supplu air temperature. so if the return air is 70 degrees, then your supply aair can be anywhere from plus 40 degrees to plus 70 degrees. you can then check and then change the blower speed to get the best temp rise.
Old 02-07-14, 03:28 PM
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And I'm wondering if they did the conversion correctly? Not that I'm a furnace guy....
Old 02-07-14, 05:58 PM
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You say you have to get up on a ladder to feel the air from the registers. Are they ceiling mounted? Where are the returns?
If both are high, you are always going to have trouble heating. The heat comes out of the register, runs across the ceiling, & right back into the return. High supplys & high returns work fine for cooling since the cool air wants to fall naturally but for heating, it is the absolute worst design you can have.
Old 02-12-14, 10:25 PM
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It's important to make sure the furnace has the correct orifices in it.

After that, the contractor should verify that the btu output matches the nameplate - airflow must be determined (by checking static pressure or otherwise), along with temperature rise.

If the furnace is doing what it should, you have a ductwork issue.

Heating in texas requires a much lower blower speed than cooling; if the ductwork was sized properly for cooling, the registers might be too large to get proper air velocity in heating mode. With vents on the ceiling, the warm air has to come out with a fair amount of force to heat the entire room properly. (return air near the floor can help with that)
Old 02-12-14, 10:28 PM
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The duct layout is too small to see - could you post a larger version?

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