Need advice. Two reputable dealers have conflicting advice.
The problem: 35 y/o ranch house with a 12x20 addition to the master bedroom for a long larger bedroom and bath. Currently has three registers,the two that go to the end of the bedroom and the bath are served by two insulated flex ducts that go through the unheated crawl space of the addition. The third duct remains in its original position. They tapped these flex ducts off the ducts that were at the outside wall prior to the addition. The ducts [about 23 ft long from the supply trunk] don't seem to have very forceful airflow and the addition portion of the room is never as cool or as warm as the rest of the house. The temp differential can be 4-6 degrees on really cold or warm days. The addition has three sides to the weather. I know most people are not fans of air boosters but I have been using a single small surface mount register booster that really changes the temperature of the addition potion of the master br up to that of the rest of the house.Only bad things are that it is noisy and the bathroom doesn't change its temp. Rest of house is very comfortable. Have a 400 sq ft north facing sun room that currently is served by a 21 yr old 80% 71k btu Carrier furnace and a 2 ton a/c unit. Has 3 large skylights and windows all around. Rest of house has a 119k btu 80% Carrier furnace and a 4 or 5 ton lennox a/c[label unreadable for size of unit]. The entire house is about 3000 square ft including the sun room.
One contractor says that he would leave the sun room on a separate furnace since it would give us the best control. Even though he sells ECW zoning he said we would be better of with increasing the supply to the addition in the master bedroom by running an additional 8" supply directly from the plenum giving us an additional register at he end of the bedroom and the end of the master bathroom. This would give a total of 5 registers [2 new 3 old and weak] for the 500 sq foot master. I thought this would work. He would use a 105k btu 90% rheem mod variable speed and a 3.5 ton 12 seer rheem for the main house and a 2 stage 50,000 btu 80% rheem and a 1.5 ton 12 seer rheem a/c for the sun room. He thinks the variable speed will solve 90% of the problem. He didn't do a manual J but the rheem mod will tend to compensate for that.
The other contractor who also seems to know what he is talking about thinks we should replace both furnaces and air conditioners with one a/c and furnace and zone [honeywell] the sun room 400 sq ft on one zone, the 500 sq foot master on one zone and the 2100 sq ft rest of the house on one zone. He is willing to do a manual J if he gets the job to finalize the size of the units. He initially proposes an american standard 90% 2 stage 112 btu variable speed and a 4 ton American std 12 seer a/c. He thinks that if we don't zone we will have the same problem when we are done since we have 3 sides to the weather and we will cool in the winter and heat in the summer faster than the rest of the house. Says that the zoning will solve our problem by allowing the furnace or air to turn on when the master needs it without waiting for the whole house to chnage temp. He will however run an new 8" supply from the plenum and run 3 registers off the new supply which will give us one additional register for a total of 4 registers [3 of the new 8" supply and one decent old register] in the master. Wants to use a bypass humidfier which will serve as a mini bypass damper. He seems very certain that this will work. I am concerned about trying to put 4 tons of cooling into the sun room or master bdrm. He says honeywell has a temp sensor in the plenum that will shut compressor or burners if certain temp are exceeded but the blower will run on to warm or cool the HX. Doesn't this sound like short cycling. Unless your zones have about the same load it would seem like this would always happen. Thinks we probably won't need a true bypass damper. Is it hard on the compressor or the gas valve and ignition to keep going on and off frequently. Can you get consistent temperatures with zoning as with a dedicated furnace. Unfortunately our basement has finished ceilings so access to the ducts is ltd.
They both sound reasonable and are the owners and have good brands with 10 yr parts and labor. We have no experience in zoning and it seems that people don't have as much experience with variable speed blowers and zoning. The one furnace system and zoning wll be significantly less expensive initially but seems more complex and trouble prone. The other choice is more expensive but I like the Rheem mod based on what I have read here. That will be an expensive mistake if we need to zone in the future if the second contractor is correct. The second contractor will do what first proposes but we will be responsible if it doest work. I apologize for the long question but this is a complicated expensive decision for someone who doesn't have the experience or knowledge. Any comments are appreciated.