Well, what is it? Not insulated, dirty, wrong color... he should pick a story and stick with it.

Two other installers can work with what you have... I think you have your answer.

What size is the new furnace and condenser?

Is the duct work in conditioned space? If not it should be insulated. Your existing plenum seems small. Does the contractor plan to make it bigger? A contractor who is telling you your duct work is too small want to do a good installation. Have him explain what he wants to do and the reasons behind it.

Mike_Home:

The proposed replacement is virtually the same size as what's there.

He did explain what he wants to do and why... and it sounds suspect - including that it's dirty.

If it's not in a conditioned space, it should be insulated and the other quotes include wrapping the plenum.

By size I meant the number heating BTUs and cooling tons. You don't want to connect your new equipment to undersized duct work. The current plenum will barely support a 2 ton AC. If your AC is bigger then you should be increasing the size of the duct work.

Are you saying the current furnace is installed horizontally and the contractor wants to install the new one vertically? What is his logic for doing this?

I have to agree with Jake some of the reasons are suspect. You don't have to install new duct work because its dirty.

Sorry, I didn't make myself very clear on the horizontal/vertical thing. The air handler/coil enclosure is taller than it is wide. The guy is telling me that the one he is installing is wider than it is tall, so he claims that he would have lay it on its side with he fan axis running vertically, which it isn't designed to do, or block off part of the area, which is what he claims the other guys were probably going to do. I may be misunderstanding him completely, and more follow up reveals that one of the plenums he wants to replace is an outlet plenum. Sorry to be so confused.

The rest of his bid and inspection was much more complete and thorough with all the parts listed and he just seemed much more professional in his approach. He is the only one that seemed to pick up on and include in his bid that one of my lineset was too small, that part of my exhaust flue was not double walled, and he is also the first one to mention that the ducts needed insulating. He is also the only one that did a part J calculation and he spent about an hour longer with me (measuring windows etc.) than the other guys did.

I went online and read about the lineset size in the install manual for the equipment and he was right that they called for a 3/8" liquid line and I have a 1/4" one there now. I called the other two guys quoting the same equipment and they agreed that the lineset was too small and increased their bids by about $250. By the time I got finished asking the other guys about all the little details, and negotiating down the thorough guy, their bids were within a few hundred dollars of the guy who was more thorough to begin with, so I ended up going with him. He also offered 36 month interest free financing included in his bid (worth around $300) vs the other guys' 12 months. Hopefully he isn't jerking me around, but I suppose its all moot now, although I haven't signed the contract yet.

All of these guys are supposedly reputable dealers, and recommended by publications and a home fixit radio show, and have been in business a long time. Hopefully I made the right decision, but my wife is getting hot and my unit died last week so..

This post was edited by smyrna5 on Wed, May 14, 14 at 18:11

The size of each AC unit is 2 tons (one in the attic) and the crawlspace is unconditioned space. Two 13 SEER Ac units, 70,000 80% gas furnaces (one in the attic and one in the crawlspace).

This post was edited by smyrna5 on Wed, May 14, 14 at 17:58

Sounds like he's limiting his options by sticking to one equipment manufacturer. I'd go with one of the other guys.

mike_home

To be honest, its not completely clear whether one of the other quotes include wrapping the existing plenum, although we discussed it. Several of the quotes I got were very minimalist as far as all the details on paper went. guess that is one of the reasons the other guy impressed me - he wrote down exactly what I was going to get including all the little details.

I'm certainly not an AC/Heating expert, but I do have some engineering background. I can only imagine how much of any of these proposals the average homeowner understands.

I still don't fully understand the horizontal vs. vertical issue. Most furnaces can be installed horizontally and can be modified so air is flowing to the right or left. It sounds like the contractor wants to modify the duct work so it will work correctly. Keep asking questions and make sure it makes sense to you.

This was a good lesson that bids for the same job may not be the same work. You really have to understand what you are getting from each contractor in order to make a fair assessment on comparing the bids. We all want to spend the least amount of money on replacing our HVAC systems, but sometimes it takes a little extra money to do a proper installation.

Your engineering background means you understand the basic laws of physics. You don't have to be an HVAC expert to ask questions and see if the answers make sense.

Good luck on your installation. Let us know how it turns out.

Thanks mike_home and others who answered. I studied thermodynamics, heat transfer, and all that theoretical stuff in college, but looking at this system has been an education in practical application of what all those HVAC engineers have designed.

I don't fully understand the plenum problem yet either, but I'll talk to him some more about it. I feel good enough about this guy to let him go ahead and begin the install next week. The fact that the other low bidders said they didn't need to change that lineset that the manufacturer said was too small, and that they had to increase their bids for that and other things this guy found after them really bothered me. Its possible they would have done it right, but how can you tell if they do such minimalist bids that leave out all the little but important details on paper? I'm spending 8 grand on this thing and want it done right.

I'll let you guys know how the install comes out.

This post was edited by smyrna5 on Thu, May 15, 14 at 8:59