Like the title says:
Like the title says:
going from 80% to 92% just doens't save that much and creates too many headaches in some retrofits.
Better to have a rule that requires proper load calculations and spend some money educating the public. You can save 5-10% effciency properly sizing.
Even better, just ban furnaces over 100k BTU and force people to actually improve insulation, size properly or install zone controls if needed. Give incentives specifically for the purchase of 40k and 60k furnaces. IT might force mfgs's to increase their 40k offering, and even offer a 40k with a 4 ton blower or come up with more innovative products like a package airhandler with a built-in combi boiler. You have package geothermal with desuperheaters, why is it such a stretch to have the tankless unit packaged with piping, valves, pump and expansion tank all together. A tankless is really just a modulating furnace with a water cooled heat exchanger, but with extra controls to measure water flow.
Motoguy, you're onto something. They could make a maximum sizing rule based on sqft, location, and age of home. Allow so many BTU per sqft and fix the house to keep the occupants warm. In the south a 40k would serve most of the homes, yet you see them ararely installed. Somehow a 10KW of heat is plenty of heat in an all electric home, but if gas is installed the furance has to be at least 60k??
On the cooling side a house that's reasonable tight and well insulated can get 1,000sqft out of a ton of properly installed AC for a 20 degree split indoor/outdoor. Yet the 500sqft per ton rule that's been used since the 60's is still used most of the time.
bracketing home sizes and setting maximum equipment sizes, IMO is just the same as having mpg limits for cars and makes even more sense than equipment effciency ratings. We have R value minimum requirements, but not how tight you make the home, no limits of solar heat gain, etc. We have standards for individual components, but not the whole.
Maybe you could start simple. Perhaps give bigger rebates or tax credits for smaller equipment. So a 1, 1.5 or 2 ton unit and a 20, 30, 40, 60k BTU heating plant would have a higher incentive. Oh.. and mfg's would be compelled to start actually making smaller furnaces, or packaged boiler systems.
We have packaged geothermal units and air to air AC, why not a packaged boilers/air handler unit. Just drop it in place, and hook up domestic water, electrical, and then install the split condenser (SC or heat pump) and an outdoor temp sensor. Give it a communicating controller and then the unit adjusts water temp according to demand and outdoor temperature as long as it stays above minimum fire. All expansion tanks, check valves, isolation valves, pumps etc. would be included. All pre-insulated. You could even include a small 2 gallon buffer tank and small pump for optional domestic hot water recurculation as well as connections for external heating loops.
Nice idea, but it seems manufacturers are going the other way. Trying to make equipment as compact as possible at the expense of airflow. Things like 14" wide cabinets for 1200CFM of airflow. You have to put at least a 17" wide coil on it, what gives? Firstco offers air handlers with water coils, a step in the right direction IMHO. Add a demand water heater and you have heat and domestic hot water.
Moved to General Discussion forum.
Energy illiteracy is the greatest impediment to properly sizing furnaces.
Most salesmen and installers probably don't even know how to convert between kw, BTUs, and tons.
They probably don't know much about residential construction, so you can forget about accurate load calcs; garbage in = garbage out.
Even 60k BTUs at 95% is an enormous amount of heat -> equivalent to over 11 1500 watt space heaters running on high continuously. :eek:
To add to the problem the differnce in wholesale cost between a 40, 60, and 80k is minimal. It seems like the larger blower/motor adds more to the cost than the extra burners. Of course the extra ductwork DOES cost significantly more, but who needs that? Lets cross our fingers and hope the furance never runs long enough to hit high limit, or if it does that the customer doesn't notice. Manufacturers have caught onto this and have lowered the tempature that high limit shuts down the furnace in order to reduce heat exchanger warranty claims.