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Old Home Needs AC Upgrade. HELP!

Post in 'DIY and General non-hearth advice' started by ckdeuce, Apr 23, 2008.

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  1. ckdeuce

    ckdeuce Feeling the Heat

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    I just bought a home that was built in the early 1900's. It has two gas furnaces that heat the home. Both are old non-efficient models that I plan to remove and install one High-Efficiency model. I also would like to add central air conditioning to the home. He is the problem. The home has no cold air returns other than one huge grate that is in the floor on the entry level of the home. It feeds both existing furnaces. There are no other returns throughout the home. Any quick solutions? I have heard about a high velocity system that uses 2" pipe. It goes in the attic an hooks to an outside condenser. Any thoughts about those systems?

    Thanks in advance
    Deuce

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  2. begreen

    begreen Mooderator Staff Member

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    This can be done with a conventional system probably. Most important is the location of the current supplies registers. Are they on the outside walls? Are there any upstairs? If the supply ductwork is sized correctly, then adding a second floor high return may be possible by running it up a first floor closet or other area where it can be boxed in. One thing you might consider is a heat pump system with the high-efficiency gas furnace as the backup heating for when it gets below 30 outside.

    I'd recommend having a pro come in and see if the current ducting is usable or not. And have then do a thorough analysis on the alternatives like a heat pump. The cost will be more, but the payback could be much quicker than a straight A/C addition.
  3. sylvestermcmonkey

    sylvestermcmonkey Member

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    Your house may not originally have had supply ducts at all. That large grate in the floor was common in older homes and served to allow warm air to rise from a stove in the cellar. Someone wisely pressed it into service as a return. If you have natural gas I would install a high efficiency furnace. It will likely pay for itself in a few years vs. using your two old ones. As for central AC, I have seen the high velocity system you refer to (a Trane, I believe). It works very well. You can put the ducts almost anywhere. It's ideally suited to retrofit older homes.

    I had a heat pump in a new construction house in eastern PA. It was the latest and greatest highest efficiency unit. Fortunately I only spent one winter there. That January it ran constantly and my house never reached an acceptable temperature. I mean constantly - it didn't shut off for a single minute, three weeks straight. My electric bill was nearly $500. The builder insisted it was working correctly but it was clearly unsuitable for the house. I was always cold, all winter long.

    Heat pumps are a fine idea and may work for some parts of the country but not here in PA. When I looked for houses recently, I completely ruled out any with heat pumps, no exception, and would do the same today. No heat pumps for me, ever again.
  4. Redox

    Redox Minister of Fire

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    Deuce, is your home set up as two zones or is it just two furnaces tied together into one duct? If it were two separate zones (say upstairs and downstairs), I wouldn't change it as zoned heat is more economical and works better. If you have two furnaces tied together to make capacity, you might be able to replace them with one high efficiency furnace, especially if you have added insulation and other improvements. I would recommend doing a heat load calculation to see what your losses are and size accordingly.

    Adding A/C to an older home can be difficult if the ductwork is less than ideal. Those high velocity systems are good for older homes if you have to snake ductwork down through a wall (thus the 2" duct size). The friction losses are higher and you need more fan horsepower to do it as well as all new (expensive) ductwork. Those 2" ducts are pretty pricey compared to conventional ductwork, but are a lot easier to install. If you have the room in the attic, you might consider a conventional heat pump with minimal electric heat for the second floor. The cold air tends to drift downstairs and cools the whole house on all but the hottest days and gives you a second zone of heat at the same time. Of course, if you can run the ductwork down through closets or box it in, it will work even better.

    This approach may be overkill for NW PA, but it will work the best and cost the least to run. Our house here in MD was done with the old GE Airwall system in the basement that uses 4" ductwork to go up 2 1/2 stories. It ran continuously and the second floor never got really comfortable in hot weather. I put in a heat pump in the attic and never got around to hooking up the electric heat. We don't really miss the electric heat much. It does get a little chilly when the unit defrosts, but I hate the thought of using electric heat. I think it works very well in our situation.

    Heat pumps are hard to get used to, especially if you are used to oil or gas heat or live up north. They are usually sized to handle the cooling load and will be undersized in cold weather. If you oversize the unit to cover the heating loss, the unit will not run long enough in the summer to dehumidify the house. They are not much more expensive to install compared to an A/C unit and can save you a lot of energy in the spring and fall. If you put in a conventional furnace and a heat pump, you will need what's called a fossil fuel kit. It's basically an outdoor thermostat that shuts off the heat pump when it gets colder out. Usually the stat is set at about 30 degrees as this is where the heat pump usually falls short and you start to need backup heat. I have mine set at apout 40 because the unit starts defrosting a lot between 30 and 40 degrees. You can adjust it later if you want.

    The big name in high velocity systems is Unico, though I seem to recall another similar system. http://unicosystem.com/ They are very highly engineered and need to be well thought out if they are going to work well. Shooting a hich velocity stream of cold air into a room is not without its problems, but they do dehumidify like nothing else out there. Sit down when you look at the quotation, though. Around here, they start at about $10k and go up, depending on the complexity of the install.

    Hope this helps!

    Chris
  5. ckdeuce

    ckdeuce Feeling the Heat

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    Very much! Thank you. My current home uses a heat pump.... We have been happy, but it is a small 3 BR ranch with a finished basement. The current setup in the old home (4BR upstairs and 5 large rooms down) is is a two zone system. One heats the downstairs, and the other heats the top. But.... They both pull from the one and only cold air return that is in the entryway of the home. From there, it gets heated then spread to the two different zones. I have a guy from my local heating co. coming on Monday to take a look and give me ideas. I can get HVAC at almost cost, and am very handy. I plan on doing all the work myself except hooking up the copper lines. Thanks again

    Chris
  6. mikeathens

    mikeathens New Member

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    My old 1870 log cabin had zero ductwork when I moved in. I had some problems to over come, like, how do you put ductwork inside the walls (logs) and how do you run ductwork between sections of the house (I didn't want to cut holes in old growth, 24' logs).

    The solution was to run returns through a downstairs closet, and then have them terminate on the floor in the upstairs; rigid heating ducts were flush-mounted upstairs. My plan is to build a closet around them to enclose them, and have the registers on the face of the closet.

    Get a good professional HVAC person, and I'm sure they will tell you they've seen this same thing before.

    I was skeptical that our system would perform well, but I'm happy so far. It was impossible to run duct work to the back of our house with concrete slab and flat roof, so in the winter it might drop to 50 while the front of the house is at 68 (if we rely on the heat pump during one of those very rare occasions - like wife going into labor). Otherwise, it's wood all the way!!!
  7. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    If you know your fuel cost and efficiency on the fossil fuel side, and your cost per khw on the electricity and HSPF, you can calculate the "crossover" point to set the outdoor thermostat.

    SpacePak is the other big name.

    My personal preference is the less-well-known Hi-Velocity, as they are dramatically more energy-efficient than the other two.

    For conventional, I really recommend the Nordyne product line. They are sold under Westinghouse and Frigidaire brand names, around here. The two-stage equipment is slick and efficient, and has a dehumidification terminal that allows you to force it into dehumidification mode (runs the A/C, but with the fan speed on slow) which makes up for the lack of dehumidification that sometimes results from heatpump sizing requirements.

    I'm going to be putting their 23+ SEER system in my house this summer, most likely. That one has a bit of a price tag on it, but it does pay for itself in the long-run, in many cases.

    An interesting thing to note is that the high-SEER equipment which uses variable-speed or two-stage operation of the condenser actually pays off better in this area than it does down south. In hot areas, the ability to throttle isn't all that critical, but up here where we can have a few months of "moderately hot, but not roasting" temperatures, the ability to run at part-capacity is a big bonus.

    Joe
  8. Redox

    Redox Minister of Fire

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    AAAHH, yes; the Space Pak! Used to be owned by Dunham Bush, IIRC. Couldn't remember the name.

    The "economic balance point" can be calculated, but the "comfort" point varies with each install and customer preference. Between about 30 and 40 degrees, the unit defrost cycles can get really long, expecially if the humidity is up outdoors. I'd rather be burning something else than putting up with 10 minute defrost cycles. YMMV

    I couldn't find any specs on the Hi-Velocity system, but it appears they are using a high zoot ECM fan motor which should save a few watts on the fan. Since it doesn't appear they are building condensing units, I can't believe they can improve on the other Mfg efficiency numbers. Not sure how dramatic the difference would be on the fan motor. You still have to squeeze all the air through the same 2" duct, consuming more HP than a low static system.

    Two speed cooling is really good at improving efficiency, as your unit runs at low speed for 80-90% of the time, and it is very efficient at this speed. Dehumidification tends to suffer on low speed, though, necessitating the extra controls. My parent's 2 sp Carrier seems to run in dehumidification mode almost all the time. Something about an 1860's farm house just seems to invite moisture in. Carrier tried inverter driven compressors back when I was in the business and our Lennox rep had numbers showing it would never pay for itself before it broke. I'm not sure that anyone had much success with VS drives on compressors, unless it was a large centrifugal unit. Two speed is much simpler and almost as effective. Oil return at low speed can be a problem, especially in a heat pump.

    Joe, that 23 SEER Westinghouse might be a record setter. How long has it been out? This is the first central unit I have ever seen with a rotary compressor. I couldn't find anything on the compressor warranty. I would hope it's 10 years for the money this baby probably costs. Nordyne used to use a tandem scroll for two speed operation, but then you had to buy two compressors.

    As long as we're plugging brands here, anything with a Copeland scroll compressor is good in my book. All the manufacturer is doing is buying the parts from someone else and putting it in their box. Copeland has the longest and most proven track record on this technology. They are supposed to be bringing a modulating scroll to market that is supposed to be the cat's pajamas, but I have yet to see any OEM's pushing it yet. DISCLAIMER: I don't sell residential equipment.

    Chris
  9. BrownianHeatingTech

    BrownianHeatingTech Minister of Fire

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    Yeah, the final adjustment should be up to the customer. Everyone's comfort level when dealing with temperature swings will vary, and the length of the defrost cycle relative to the heat demands of the house will vary for each particular installation, to some extent.

    The economic balance point gets you in the ballpark, then the fine-tuning is a matter of moving the adjustment slightly over time.

    They are over 13 SEER, as opposed to Unico and SpacePak which have exemptions allowing them to sell equipment that doesn't meet the Federal 13 SEER minimum. If you run the numbers for the Hi-Velocity stuff on the ASHRAE website, you can even get them up to 14-15 SEER, if you use the right condenser.

    Inverter technology is making a comeback. With prices the way they are, it does pay off. The Fujitsu 21+ SEER mini-splits run very slick on that inverter system they have. I have a customer who heated his house this past winter using three 1-ton units (adding $500 to his total electric bill for the whole winter) and 170 gallons of oil. The previous year, he burned 900 gallons of oil. Granted, in his case a lot of the savings involved shutting down the heat to everything except the master bedroom during the night, using the oil furnace just to reheat the house in the morning, and then relying on the heat pumps to heat the place for the rest of the day. And, of course, relying on the oil furnace during the very coldest weather. If he wasn't retired and had to heat more of the house during the night (kids rooms, etc.), the electric bill would have been higher. Atypical situation, but it ended up working out very well for him. Particularly since we sized the equipment for A/C, with no intention of it being used as heating except in the mildest weather, and his experiment in using it for heat was entirely his own doing.

    It's been out a couple years, at least, if I recall correctly. It's a matched system, with a specific condenser, evaporator, and a wall-mounted "thermostat" which is actually a computer that controls the whole thing. Good bit of wiring involved, so it's important to pay attention to the details. And, of course, to size the ductwork correctly. No sense having an ECM blower motor if it has to run at high speed all the time, just to force the air through restrictive ductwork. When I install mine, I'm going to have to replace all the existing ductwork, because the static pressure will be too high with the junk that was installed here. It will also only be for the first floor, since the ducts to the second floor are in the walls, and too restrictive to bother trying to shove A/C through.

    Joe
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