Advice needed on a Replacement System
I am limping along with a 100K Bryant 90+ furnace and a 4 ton 10 SEER AC unit. The house is ~ 4300 sq ft. with three zones of similar size. The furnace has a bad secondary HX and the compressor was making bad sounds at the end of the cooling season. Located in Michigan. Since the house was new in '94, the outside walls have been re-sided with 1" foam (taped) added, windows properly sealed, additional ceiling insulation added, etc. to minimize air infiltration and improve insulation. I have just received three quotes with multiple options in each and am overwhelmed with the choices of Bryant, Amana, and Lennox and a huge range of manufacturer rebates, tax credits and Utility rebates. I have been on a steep learning curve in the past few days and stumbled across this site which appears to contain excellent advice.
One of the contractors has performed a load calc (do not know result yet) but the other two have just responded with 100K and 110K for 90% - 98% AFUE furnaces.
On the A/C side, the options range from a 13 SEER to an 18 SEER two stage 4 ton unit with significant increases in price. We typically only use the A/C for 4 months a year and are on the boat for two to three of those with the thermostat set at 80 deg. F. On the heating side, only the main floor is heated to 70 deg. F consistently. The other two zones are maintained at ~60 deg. F with mostly damper bypass and the occasional damper opening from observing the system. These two zones are used at 70 deg. F about 25% of the time.
Our zones are configured with a total of five dampers on the duct runs. There are no dampers on the returns. The dampers and control board are Honeywell Trol-a-Temp. We have three Honeywell Chronotherm III thermostats
Our "Best" Lennox quote is for a SLP98 110K and an XC16-48 with icomfort Wi-Fi thermostat; the "Next Best" is an EL296 110K and an XC16-48 with a CS5000 thermostat.
Another "Best" quote is for a Bryant 987MA Evolution and a 187B Evolution AC with the option of a Wi-Fi thermostat and and new zone dampers at a huge upgrade cost.
Another "Better" quote is for an Amana AMVM 96% and a ASXC18 AC again with the option for a Wi-Fi thermostat and new zone dampers.
Does anyone have any input to help me make a choice? I am particularly interested in:
1) Should I get an load calculation for each quote? I am a bit concerned about going with a 110K when the existing 100K 90% unit has worked well and I have made some improvements to the building envelope.
2) Will a two stage A/C give me significant improvements in my circumstances?
3) Will the best Lennox system with a Harmony III control work with the existing zone dampers and maintain all of the features/capabilities of the furnace?
4) Do I need to install new dampers, etc with the Bryant and Amana systems?
5) What thermostats/sensors would be the best choices for each proposed system?
Obviously up front cost is a factor in my ultimate decision but we plan to be here for the life of the system (15-20 years). I want to end up with a high quality, efficient and reliable system that takes into account total ownership costs. I do not want to end up with the "ultimate" system that can never pay back its increased cost over its life.
I probably have not asked all the right questions but hope to learn from your expertise so I can ask some more of the right ones.
Thanks for any advice you can give me.
1) Should I get an load calculation for each quote? I am a bit concerned about going with a 110K when the existing 100K 90% unit has worked well and I have made some improvements to the building envelope. I highly recommend getting a Manual J from any contractor. One you have made some adjustments with your insulation and other improvements. Each of the three brands you have bids on do not all produce the same amount of cooling; close, but a manual J & S will be the first start to verify if the equipment selected is the correct fit.
2) Will a two stage A/C give me significant improvements in my circumstances? 2-stage equipment is nice, but if it is not in your budget look at a single stage system, but I do recommend the variable speed furnaces they seem to be quoting. However, if you are going to keep 3-zones then the Lennox Harmony will require a 2-stage condenser. Another unit by Amana would be the ASXC16
3) Will the best Lennox system with a Harmony III control work with the existing zone dampers and maintain all of the features/capabilities of the furnace? I like this option in that it does not require a by-pass and yes the honeywell ARD's (2-wire) will work with Harmony. The Harmony board will even work with your existing thermostats. ** another reason to get a manual J is so the technician can properly adjust the dip switches for the zoning board. Hopefully it was your Lennox contractor who is running the manual J.
4) Do I need to install new dampers, etc with the Bryant and Amana systems? I am not 100% on Braynt's model #'s, but if it is similar to the Carrier's Infinity yes new dampers. 3-wires. Amana will most likely be using a 3rd party zoning like Honeywell or something else. You can go back with a new Honeywell zoning.
5) What thermostats/sensors would be the best choices for each proposed system? Most of those quoted are good. Will you be using the Wi-Fi feature for your thermostats? A good programmable thermostat is all you need. On the Lennox the Icomfort is great, but I like the CS7000 over the 5000. I believe Amana has a new stat from Emerson that is good too.
1) I suspect that heat capacity required is << 80,000 BTU/ Hr with ALL heat zones at 70'F.
Originally Posted by senojev
_ What is your current usage of natural gas per month?
_ Does your current system run more than 40 minutes out of an hour when it is 0'F outside?
_ ... No, .:. 80,000 BTU/Hr is More than adequate.
_ I doubt that selecting lower capacity would provide the needed air flow for A/C.
_ I believe that the Bryant model 987MA will provide the efficiency and Comfort that you're looking for.
2) NO, not in MI. Does your current A/C system consistently provide < 50% Relative Humidity?
It's Not Rocket Science, But It is SCIENCE
with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE
Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities
i would want a load calculation, i would also want a 2 stage furnace .as for the ac 2 stage ac systems do work better with zone controled units .i would also upgrade the trol a temp the bryant evolution with the zone control is a very nice set up
Made the decision and now the proud owner of a new furnace and A/C
Thanks for the advice, particularly to get a load calc.
Originally Posted by catmanacman
The guy doing the load calc came up with a 70K 96% 2 stage unit which provided some margin and a 4 ton single stage A/C. and decided to go with him. Was just not happy with others who seemed to oversize the furnace. Contractor did an expedited install of the furnace Thursday as my existing furnace had died completely, working until 6:30pm to get it wrapped up after finding some zone problems. Very pleased with the quality of the work done by the two installers and a service tech.
Even got a "free" energy assessment Friday with blower door test, etc. that lasted over four hours.
I suspect the 100 and 110K units proposed by others would never get out of first stage or would never modulate.
After a night of 4 deg. F temps, furnace ran fine and had no trouble keeping up with demand so sizing looks OK. Will look even better when I get my ductwork sealed and air infiltration reduced.
Thanks again for the feedback provided by the forum members.!
Make sure the 70K Furnace has a 4 ton blower drive on it. Many contractors will not match up the airflow of the furnace to the AC. I know a lot of brands do not have a furnace that small that has a 4 ton blower on furnaces below the 80K size.
If you go with a modulating furnace the new thermostats may not work with your existing zoning or not provide all features. Most modulating furnaces communicate and do not use 24V systems.
70K and 4 ton in Michigan aren't making sense!
I agree with Baldloonie. Something is missing here. Doubt if this is last time forum hears from OP.
I would be interested in knowing exactly what models were installed and scope of work.
Originally Posted by BaldLoonie
Can you tell me what does not make sense?
Some info on house: 4350 sq ft. on three levels, 1900 on each of two lower levels, balance on top level. Lowest level is at least 50% below grade with full exposure to west. House is 2x6 construction, R-19 walls with 1" taped foam over 5/8" OSB, fully taped Tyvek, low E Pella windows. Attic space is heavily insulated ~ R-50. No windows on N, three on E, two on S and W wall is about 30% glass.
Blower on the furnace can handle a 4 ton A/C per my contractor.
Thanks again for the responses.
20 yr old house in Michigan. Installed a Bryant 986T, two stage furnace with a Bryant 116B A/C with the recommended coil, new lines, Aprilaire MERV 10 filter and Aprilaire 600 bypass humidifier.. Currently using old Chronotherm III thermostats with a Honeywell Mabs II control board for three zones.
Blower door test shows about 4 ACH 50 pascals if that helps. Can drop this to less than 3 by taking care of three or four big air leaks.
Clarification - Furnace is an 80K - load calc showed 70K would work.
Originally Posted by senojev
To your south, where it is a tad warmer in the summer and warmer in the winter, I don't think I've ever seen a combo like that sold. If a house is so well built that despite its size can heat on 70K, sure ought to cool with less than 4 tons. I'd expect to see your combo much further south. Just seemed strange...
So Far So Good
The 80K furnace handled some recent sub zero weather with no problems heating all three zones and did not run at high stage continuously. I would have to conclude that it is sized OK. I guess I will have to wait for the warm weather to see how the AC performs.
Originally Posted by BaldLoonie
Thanks for your input.