The Cedar Rapids station in NOAA's data
NOAA's engineering weather data includes a station at Cedar Rapids, recorded at an elevation of 869 feet. For that station it gives a 99% winter design temperature of -5°F. On the cooling side it gives a 1% summer design temperature of 89°F, paired with a mean coincident wet-bulb temperature of 74°F. The same data counts, in an average year at Cedar Rapids, about 355 hours with the wet-bulb temperature above 73°F and about 1,124 hours above 67°F.
Those are the station's figures as NOAA publishes them. Everything below is about your own house and the people you invite to bid on it.
Notes worth making before the first visit
You know the house in a way no estimator can learn in an afternoon. Spend a few weeks jotting down what you notice, then hand the same sheet to everyone who comes out:
- The rooms that never match the thermostat, and whether the problem shows up with heating, cooling or both.
- Upstairs and downstairs differences, and the times of day they are worst.
- Drafts at windows, doors, outlets and the attic hatch.
- Any rooms you have finished, added or closed off since the current equipment went in.
- What the furnace or heat pump sounds like when it starts, while it runs and when it stops.
- The model and serial numbers from the labels on the indoor and outdoor equipment, and the age if you know it.
- A year of gas and electric bills, if you can pull them from your utility accounts.
A sheet like this keeps each conversation on your complaints instead of on a brochure.
What the load calculation ought to tell you
Ask whether replacement equipment will be sized from a room-by-room heat loss and heat gain calculation, often called a Manual J, rather than copied from the nameplate of the unit coming out. Questions to put to each bidder:
- Will you run that calculation for this house, and will a copy come with the bid?
- What outdoor design conditions did you enter, and what source did they come from?
- Did you measure the insulation, the windows and the air leakage, or assume them?
- How does the size you recommend compare with what is installed now, and why?
- If I air-sealed the attic or added insulation first, how would the answer change?
A contractor who rounds up "just in case" owes you an explanation. Oversized cooling can reach the thermostat setting quickly and shut off before it has pulled much water out of the air, and an oversized furnace can cycle on and off more than it needs to.
Choosing the heat source
Heating bids may arrive in one of three forms, and each one deserves its own price line:
- A gas furnace with a central air conditioner. Ask for the furnace's AFUE rating, whether the blower is variable-speed, and whether the burner is single-stage, two-stage or modulating.
- A heat pump with electric backup. Ask what capacity the heat pump keeps at low outdoor temperatures according to the maker's published data, how much backup heat is included, and what tells the backup to come on.
- Dual fuel. A heat pump carries the load until a set outdoor temperature, then a gas furnace takes over. Ask where that switchover point will be set and why, and whether you can change it later.
For every option, ask for an estimate of yearly running cost worked out on your own gas and electric rates, and ask to see the arithmetic. Ask, too, which federal efficiency minimums apply to the equipment being quoted, and get the AHRI reference number for the exact pairing of indoor and outdoor units so you can look up its rating yourself.
Keeping summer air dry
An air conditioner removes moisture as well as heat: water condenses on the cold indoor coil and runs down the drain. How much it removes depends on how long the coil stays cold. Ask:
- What share of the quoted system's capacity goes to removing moisture, according to the manufacturer's data?
- Would a variable-speed or two-stage system, or a slower fan setting, keep the coil working longer?
- Can the thermostat show indoor humidity or run a dehumidify mode?
- Would a stand-alone dehumidifier help in part of the house, and where would it drain?
Venting, combustion air and the flue
Any gas appliance has to get rid of its exhaust safely. If a new high-efficiency furnace is proposed, ask where the plastic intake and exhaust pipes will leave the house, how far they will sit from windows, doors and the ground, and how they will be kept clear of drifting snow. If the old furnace shared a chimney with a water heater, ask what happens to that chimney once the furnace stops using it, and whether the water heater's venting needs to change. Ask for a carbon monoxide test at start-up, and keep working CO alarms on every level of the house.
Ducts and returns
A new furnace or heat pump is only as good as the ducts feeding it. Ask each bidder to look at the supply and return runs they can reach and tell you what they find. Useful requests:
- a static pressure reading on the current system, taken before the bid is written;
- a duct leakage test, or at least a plan for sealing joints with mastic or a tape rated for ducts;
- a check on whether the return side is big enough for the new blower;
- separate prices for duct repair, so you can see what the equipment costs on its own.
Cedar Rapids on the record
Two facts about the city, stated for reference:
- The 2008 crest. On June 13, 2008, the Cedar River crested at 31.12 feet, its highest level in Cedar Rapids history. The previous record was 20 feet.
- Drinking water. Cedar Rapids draws its drinking water from shallow vertical and collector wells built in the sand and gravel deposits along the Cedar River.
Licensing, permits and coverage
Put these questions to every company before you sign:
- What state license or registration, if any, covers this work, and what is the number?
- Which city permits does the installation need, who pulls them, and will an inspector visit?
- Can you show proof of liability coverage and workers' compensation? If anything on the certificate is unclear, your own insurer can help you read it.
- Will your own staff do the work, or a subcontractor?
- What happens to the refrigerant in the system you take out?
Setting the bids side by side
Lay each proposal out under the same headings: model numbers for every piece of equipment, the efficiency ratings for the matched pair, the load calculation and the size it supports, the heat source and how backup or switchover is controlled, venting and flue work, duct testing and repair, the thermostat, removal of the old equipment, permits and inspection, the start-up readings you will receive, and the written parts and labor warranties. Where a bid is silent on one of those lines, ask about it before you compare totals.