FAQ’s for Contractors

Hamstra Heating & Cooling

The following questions are frequently asked by contractors. Simply click the question for which you would like to read the answer.

Typically our schedule runs about 2-4 weeks out during the off season (November – March) and 4-6 weeks out during the summer (April – October). On average, you should call to schedule HVAC installation about 3-4 weeks before the house you are building is ready for HVAC install.

All dropped ceilings and soffits must be built and complete, plywood roof must be on, proposal must be signed (if this is the first phase on HVAC work to be d3), and we must have dryer vent and kitchen hood locations.

Outdoor stucco must be complete, indoor paint must be complete, indoor and outdoor disconnects must be up, condenser pads must be poured and dry, rough-in portion of job must be paid in full, exterior doors must be hung (including garage doors if units must be set inside of garage). What needs to be in place before Hamstra can perform a unit start-up?

The home must have finished floors down, gas turned on, electric fired up, and all exterior doors hung.

The worst method for sizing air conditiong systems is the square footage method. This method uses a standard that 400 square feet of floor space is equal to 1 ton of air conditioning. So, using this method, a home that is 1600 square feet would require a 4 ton air conditioning machine. This is completely incorrect and is nothing more than a lazy guess. Think about it this way: I’ve got two 400 square foot buildings, one has walls 8 foot high made of double masonry block and has one tiny window and one door, the other building is made of un-insulated 2×4 walls 15 feet high and has 20 – 12×3 single pane windows and a screen door. Now, do you think it is going to take the same size air conditioning unit to equally cool both buildings? The answer is no. The second building would probably need 4-5 times the cooling capacity as the first. Many HVAC contractors incorrectly use the square footage method and that is the reason why there are so many homes out there with poor air conditioning systems. It doesn’t work unless you get very lucky, bottom line. A full Manual J load calculation is the only method Hamstra will use to size units and ductwork.

It varies based on the size of the furnace or air handler required. In general, the minimum size of a mechanical closet/room for a gas furnace must be 56″ wide by 39″ deep. This dimension only accounts for the furnace and necessary ductwork. It does not include combustion duct and flues that may be needed. For a heat pump, the mechanical closet/room must be a minimum of 56″ wide and 30″ deep.

The general rule for required attic space is; the size of the ductwork plus 18-20″ for house insulation, duct insulation and truss members. Example: 24″ tall ductwork would need 42-44″ of attic space in order to fit.

Manual J load calculation should always be used to size heating and cooling systems. It is mandated by local codes and the DOE (Department of Energy) Manual J calculates the heat loss and gain through walls, windows, floors, infiltration and the roof. It also accounts for internal heat loads such as people, appliances, electronics, etc. No other method does this. Hamstra uses Manual J load calculation to size all of the systems we install. The design conditions that Hamstra uses for Tucson are:

104 degrees Outdoor DB (Dry bulb) with 75 degrees Indoor DB, 67 degrees Indoor WB (wet bulb). These design conditions/standards are per the model energy code.

Using any other method than Manual J is incorrect and should be completely avoided. (See “Why can’t Hamstra size my units using square footage?”)

It is always best to have insulation above the ductwork at the roofline. This maximizes the energy efficiency of the home because the ductwork won’t gain as much heat from the attic space because the attic space won’t get as hot.

You need to submit a floor plan with house orientation, roof insulation values, wall construction and insulation values, window sizes, window type with U-values and solar shade coefficient, and interior elevations (illustrating ceiling heights). You need to let us know of any additional expected internal heat loads (computers, flat screen TV’s, electronics, etc.) that will be added to the home. We also need know if the customer is satisfied with the standard model energy code design conditions (104 degrees outdoor dry bulb, 75 degrees indoor dry bulb, 66 degrees indoor wet bulb). Lastly we need to know if the customer wants gas equipment or heat pump.

Yes, very much so. Example: Take a house that has 400 square feet of glass with no porch facing west versus the same house but with the windows facing north. The house with the west facing windows will need roughly 2.5 tons more cooling capacity than the home with the north facing windows.

Fresh air intake is a code requirement. The code says that we must provide 15 CFM per bedroom plus one of fresh outdoor air for the home. Example: A home with 4 bedrooms must have 75 CFM of fresh air. New homes must have fresh air intakes because they are built much more air tight than they were in the past. Fresh air intakes are ducted into the return air of the air conditioning system and the fresh air is then filtered through the systems filter.

Transfers are a means of returning air supplied to a room back to the system’s main return(s). Only about 100 CFM of air can undercut doors and make it back to the main return(s). Any room that has more than 100 CFM of air supplied to it must have a transfer in order to get this air back. If air supplied to a room cannot get back to the return, the supply air quantity will be reduced and the room will become uncomfortable. Also, the area where the main house return(s) is/are located will become negatively pressured, which can backdraft fireplaces and increase outdoor dust and air infiltration.

Hamstra uses Manual J load calculation to size all of the systems we install. The design conditions that Hamstra uses for Tucson are:

104 degrees Outdoor DB (Dry bulb) with 75 degrees Indoor DB, 67 degrees Indoor WB (wet bulb). These design conditions/standards are per the model energy code and will be used exclusively unless more stringent standards are requested by the contractor before the system designed.

Physics. Hot air rises, cold air falls. This is why Hamstra recommends separate systems for upstairs and downstairs or zone controls. It is impossible to have a balanced, comfortable system in a two story house with one unit and no zone control. Many HVAC contractors wrongly install one unit on a two story house as a way to save money. While this does indeed save on the initial cost, it will lead to an uncomfortable home that is impossible to balance. We are only interested in happy and comfortable customers. This is why we will not install a single unit on a two story application unless it is equipped with an electronic zone control system.

Different SEER options:

13 SEER – Is the minimum standard for efficiency

19 SEER – Is about the highest efficiency available

15 SEER and up – these systems typically have 2-stage cooling and heating and variable speed operation. These systems provide the best overall means of comfort and quiet operation for the money.

Filter options:

1″ pleated filter à Standard installation

5″ Filter upgrade à Is about 20 times better than the 1″ filter

Accuclean/PureAir filtration systems à Are about 100 times better than the 1″ filter.

Exhaust Fans

Standard exhaust fans that we install have a SONE rating of about 2-3 (SONE rating is a sound rating, the lower the rating the quieter)

UltraQuiet exhaust fans have a SONE rating below 1.0

Please call our office if you have any further questions on the options that we offer (520) 629-9833

We recommend no more than five degrees of change from your normal setting. More than five degrees of change could cause damage to the contents of the home, especially in the summer when we are dealing with extremely hot temperatures. Wood floors, cabinets, pets, electronics, etc. are all items that are sensitive to large temperature changes.

Your furnace smells because dust has accumulated on the heat exchanger inside the furnace. The smell is the dust being burnt off. Under normal conditions, this smell should stop coming from the furnace within 24-48 hours.

You should never close more than one register in your home if the air conditioning system was installed by Hamstra. If your duct system was not installed by Hamstra, you should not close any registers. CLOSING OFF REGISTERS DOES NOT SAVE ENERGY! If you close off air to rooms they will still have heat gain from the outside. This heat gain is transferred to the rest of the house through doors, walls, ceilings, etc. This heat gain will cause your unit to work just as hard as if all the registers were open. There is no energy savings to be gained from closing off registers.

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