I’m a long time lurker here, but this is my first post. (I’d fill out my profile, but it doesn’t seem to give me that option) My wife and I bought a 100+ year old farm house in <!—-><!—->SW OH <!—-> last fall and we are looking to update the HVAC system. Currently, we have a 30 year old propane furnace located in the basement and no AC. It’s a 2 story house, but with duct work only going to the 1st floor. There are two 12†X 12†openings in the ceiling/floor to let hot air rise to the 2nd floor. It gets pretty chilly up there when the temp gets down close to 0°! <!—-> <!—-><!—->
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We plan on switching to a heat pump and had a reliable contractor come out and take a look and give us a quote. My question revolves around getting air up to the 2nd floor. He gave us two options, a single unit in the basement or a split system with units in the basement and in the attic. If we go with the single system, we would need to build a chase to run a duct and return up to the attic then branch off to the 3 rooms. We could take a corner of the dining room and a bedroom to accomplish this. Our contractor was concerned that it would be difficult to balance the temperatures between the two floors and we would have ugly bump outs in two rooms. His suggestion is that we go with the split system to eliminate those issues and I believe he mentions that the split system would be more efficient. The split system is about 50%-60% more expensive, so I’m looking for some input to help decide whether or not the extra money is worth it.
Paul
Replies
Black46,
1. You don't want HVAC equipment in the attic, unless you are willing to install insulation between your rafters to create a "cathedralized" attic, also known as an unvented conditioned attic.
2. Ideally, you don't want any ductwork in your attic either -- although it's easier to correct for problems arising from attic ductwork than it is to make attic HVAC equiment work well. All seams in attic ductwork need to be sealed with mastic and the ductwork needs to be deeply buried in insulation -- ideally, insulation that is not vapor-permeable. (Otherwise you can have condensation problems during the cooling season.)
3. If your HVAC contractor is competent, he or she should be able to design a duct system that is properly balanced. That means calculating heat loss and heat gain for each room in the house (following Manual J), and designing the duct system using Manual D. If the contractor doesn't know what Manual J and Manual D are, find another contractor.
You might want to look at the high velocity systems. Of hand I can't remember the brand name of any of them.
But they are often used for retrofit in old houses. They use realatively small ducts and distribution systems.
I think that this is a specialty area so that most HVAC don't do it.
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
I looked into the high velocity systems a bit. One comment I came across was that when used in combination with a heat pump, the higher velocity of the ducts and the cooler output of the heatpump doesn't give you a very comfortable system. Maybe I should investigate a little further...
Paul
I agree with Martinholladay. Only offer the following. I would want the 2nd floor unit on the 2nd floor not in the attic and only run the ductwork in the attic. As Martin mentioned both supply and return lines need to be sealed with mastic and mastic backed tape. I would build chases around the duct so you can insulate the top and sides to at least an R47 with the duct resting on the ceiling joist. Two systems installed correctly will be more comfortable and more energy efficient than one system for the whole house, again the attention to the details by the installers is critical including air sealing around each ceiling penetration. Jay
Two small systems, in the long term, will be much more energy efficient than one big system. Your home will also be much more comfortable.
Conventional heat pumps do not work well below 40* or so. Yes, they still extract heat from outdoors, but the number of available btu's goes down quickly. You almost need a "4 ton" heat pump for heating and a "2 ton" ac unit for cooling- which is really hard to do in one condensing unit. That means a two stage unit... or something like this: http://www.gotohallowell.com/
If you plan on replacing your propane system with a straight heat pump in a cold climate, you better have some type of backup (electric strip or a dual fuel setup) unless you use the product in the link above. A furnace/air handler with a variable speed motor is a must to save $$$ running the fan for the heat pump as run times get longer.
There is nothing wrong with HVAC equipment in the attic, as long as there is attention to detail. Air leaks on the return side are bad in both summer and winter. Service sucks if access is not planned out. An ideal solution is the equipment on the second floor in a closet with just the ductwork in the attic.
Replacing windows and adding insulation will make a big difference in equipment sizing, so have a plan there- if it isn't done already.
Danski,
You wrote,
"There is nothing wrong with HVAC equipment in the attic." Every major study by a reputable researcher has found the opposite to be true. During the summer, attic temperatures are significantly higher than outdoors. Supply-air plenums and return-air plenums are notoriously leaky; most furnaces or air handlers are delivered leaky by the manufacutrer, and include seams that are difficult to seal. Attic installation of HVAC equipment can easily result in a 20% to 30% energy penalty, right off the bat, and can get signifiantly worse than that depending upon the details of the installation. Not to mention maintenance and servicing problems.
I also added the qualifier "With attention to detail".
That would include sealing the ducts and making sure that the insulation is done properly. Enclosing the equipment in its own insulated room would be even better.
In my experience, people will not give up the square footage on a second floor for a mechanical closet.
I suspect that all the extra ductwork required to bring the air up from the basement would have a similar efficiency penalty compared to just putting it in the attic.
Aesthetic issues (soffits and bumpouts) or a lack of interior walls, or things like steel and LVL beams in the way also create problems.
While not perfect, attic installs function just fine given proper installation.... unfortunately, there is a lot of residential HVAC work lacking any sort of attention to detail.
The heating load is almost 3 times the cooling load. The last load of propane was over $3.50/gal, so we'll be using supplemental electric heat! :o) I have sizing questions as well, but I'll probably start another thread with those.
We're working on an insulation plan as well. If we end up with a unit in the attic, we'll go with a hot roof. The house has an old metal roof that is solid and dry, but there is no venting at all. I've read through the pros and cons on different threads here about the hot roof and still haven't figured out if one way is better than the other!
If you look at the heat pump link in a previous message, they claim it works below zero.
It is a two stage design with a booster compressor.
It is supposed to deliver an air temperature close to that of a fossil fuel furnace. All of the specs are on the website.
If you are serious about an air exchange heat pump as a primary heat source, then that is the one to buy.
The multi stage design also works for cooling, so it is not oversized.
Otherwise, I bet you are looking at about 15kW (roughly 30k btu and 68A *each* at full load @ 220v) of staged strip heat on each system to make up for the deficiencies of a normal heat pump design in a cold climate- even with something like a 2/3 ton two stage condenser section.
Choose wisely.
I was reading your comment regarding Hallowell; I am building a new home & was going to install a ground source geoothermal system until I talked to a heating company I have great respect for. They showed me a fairly new heat pump system by Hallowell International (http://www.mitsair.com) model 42C/46C which they claim puts out 35000 BTU at -18C (-2F) that is less expensive than an installed geothermal system. It is also supposed to have 1/3 the operating cost. I am building in an area that gets 1- 2 weeks a year in that temperature range but I do not need it for a/c. I am leaning toward this option and am looking for input. By your previous comment I thought you might have some helpful info for my situation. Thanks in advance!
I have never used their products, but based on the specs, it is a solution for those that want a heat pump in a cold climate.
Unfortunately, my ductwork is in the concrete slab, and it will not support the airflow requirements of their larger unit. Otherwise, I would have bought one.
I have also looked at ground source geothermal, and because my heating btu's far exceed my cooling btus (almost 4x), the numbers just don't work out.
Even the Hallowell unit alone would not heat my 1200 sf home, but it would cut gas usage by about 80% or so. More if I tore down drywall and reinsulated the whole house. If only they used R13 instead of R9.....
Kinda goes back to building efficiently the first time instead of later high tech stopgap measures.
spelling edit
Edited 2/10/2008 2:22 pm ET by danski0224
One word...
MINI-SPLIT systems = NO DUCTWORK!
You could use one for the 2nd floor and have the unit outside.
He!!, You could use them for both floors and get rid of the duct work.
OK a bunch of words.
Liberty = Freedom from unjust or undue governmental control.
American Heritage Dictionary
Edited 2/8/2008 8:37 pm by Hackinatit
Fine for cooling, not so good for heating below 40* outdoor ambient.
Since you'll be installing new ductwork for the upstairs it should be a relatively simple matter to install automatic dampers so you can have split control with only a single furnace/AC. Does add $700-1000 to the overall cost, but should be cheaper than a second system.
Until they come up with a modulating damper system that interfaces with a variable speed modulating furnace and air conditioner (think commercial medium pressure loop with VAV boxes), those damper systems suck.
Current accepted practice is to size the system for the whole home, then split it up into zones. Problem is, now the large equipment is only utilized for a smaller space, so run times are short because it is oversized and the extra capacity is dumped somewhere.
Current variable speed two stage furnaces are the best option if someone *really* wants a zoned system. Those give you a smaller burner and smaller blower on the initial call for heat (and cooling if it is a two stage condensing unit)
Something better is to size the equipment for the largest zone in a 2 zone system, but now the equipment is too small for the whole space if there is a problem. You will also have stacked heat or cooling calls.
Either setup can result in equipment that doesn't shut off for a long time because it constantly cycles between zones. Efficiency gains are lost due to dump zones.
Propely designed ductwork will work on a single system home and provide the desired comfort. It has to be done right so the room furthest away from the equipment also gets the conditioned air. Proper design is hard to get in the slam bam residential market.
Two smaller systems is a bit more forgiving in the design aspect, as long as the house isn't too big.
Two smaller systems is also much more energy efficient than one large one. It costs much less to start and run a smaller compressor compared to a large one.
Some professional thermostats allow multiple daisy chained installations connected to an interface unit, and some will interface with and average a remote temperature sensor.
It is also possible to connect two stats in parallel- then the equipment will run until both stats are satisfied, but you lose the averaging capabilities of the better stats (poor man's zoning without dampers).
Static balance may work for heating but not for cooling. And certainly not when switching back and forth between the two. The cooling load distribution of a house can vary dramatically between a sunny day and a cloudy one.Besides, sometimes it's nice to be able to shut down heating/cooling of part of the house, if it's unoccupied.
If your view never changes you're following the wrong leader
I have been in two system homes that have had *zero* temperature differential between floors and rooms using nothing but plain old ductwork. Both systems in the basement... or one in the attic- no difference.
It isn't hard to do.
I have also been in homes with electronic zone dampers. The system runs constantly and some zones never satisfy.
To each their own :)
Sure you can do it with two systems. But with a single system you need way more cooling than heating on the top floor, relative to the bottom floor, and one floor or the other is guaranteed to be miserable.
If your view never changes you're following the wrong leader
Cooling loads (and heating losses) are dictated by a Manual J load calculation.
If the equipment is sized right, and if the ductwork is installed properly using design principles in Manual D, then there are no problems.
Temperature differences between floors is a result of poor design and installation only. Open floor plans and an architect that does not plan for mechanical systems can contribute to poor design and installation practices.
Edited 2/10/2008 10:15 am ET by danski0224
I don't think the sun reads the manual.
If your view never changes you're following the wrong leader
If you have done a load calculation, you would know that solar gain through windows is accounted for. There are many options that define the direction the window faces, square feet of glass area, window construction (metal, wood, vinyl), panes of glass, storm windows, glass coatings, interior shading and exterior shading.
The load calculation gives you the number of btu's to cool the space, then it is up to the designer to make sure the ductwork can deliver that number of btu's to the space.
The sun does not read the manual.
Neither do many HVAC "experts".
Edited 2/12/2008 8:49 am ET by danski0224
And how the eff does the load calculation know if it's a cloudy day or a sunny day?
If your view never changes you're following the wrong leader
It doesn't... but someone has figured out things like degree days, average local temperatures, grains of moisture, temperature swing.... All that stuff is in tables used in the figuring.
All of those things make the load calc work without oversizing the equipment.
If it is sunny, the AC works more... if it is cloudy, it works less... sized correctly, it works properly :)
So on a hot sunny day the top floor is fine, but on a cloudy (but warm) day it's an icebox.
Averages are just that.
If your view never changes you're following the wrong leader
Uhhh, no.
Equipment is sized for the hot sunny day. Thermostat controls the equipment. No problems.
On a sunny day the heat gain of an upper floor with lots of windows is greatly increased vs the heat gain you'd have on a hot cloudy day. The balance that works on a cloudy day will freeze out the bottom floor on a sunny day, or roast the top floor.
I can't believe that this is so hard for you to comprehend/admit.
If your view never changes you're following the wrong leader
It isn't hard to comprehend.
I believe it is you that fail to understand that a ventilation system will function properly if a load calculation is done on the structure, and then the ductwork is sized properly to deliver the btu's required (air) to cool/heat the space.
By definition, it is impossible to size ductwork properly without a room-by-room load calculation. Yes, there are "rules of thumb", but if someone is trying to cool a glass room, then that person had damn well better do it right.
As long as the equipment and ductwork is sized for design conditions, the thermostat will do its job and control the temperature. The thermostat does not know or care if it is shady or sunny out, unless some genius puts it in the sun... or on the outside wall... by an exterior door... etc, creating a problem.
Homes, rooms or floors that do not heat/cool well are a result of poor design and/or installation. Poor design can also encompass building features, aesthetic issues or a low bid mentality that prohibit the proper installation of the ventilation system. There is no other explanation for those deficiencies.
Even with one system for a two level house, if the ducting is sized properly for the load calc (cooling load), and good design practices are used to minimize duct restrictions (Manual D) then temperature variations can be minimized or even eliminated. Admittedly, this approach suffers in the low bid mentality environment of residetial work in general, and problems occur when the proper ductwork can't be used because the building is designed without consideration for the mechanical system.
Elecric zone dampers in the typical residential forced air application are merely a crutch to compensate for something else that is done poorly. It takes just as much effort to design a duct system for electronic dampers compared to proper design without them (download the Aprilaire zoning installation manual and read it if you don't believe me). If the duct system is not designed from the start for zone dampers, then that just creates problems, and you still have a system operating at 100% capacity being used at about 50% capacity (excluding multi stage equipment).
If you have done a load calculation, and installed a ventilation system properly, then it would be obvious that your points do not make any sense at all.
Edited 2/14/2008 9:10 am ET by danski0224
Danski, I am a homeowner building a new place, installing a damper system with a 2-stage, high-efficiency nat gas furnace (2 stories plus walkout basement). We wanted 2 zones (not enough space in the floor plan for additional duct runs). The house will be very well insulated with closed-cell spray foam.The HVAC contractor suggested either 2 smaller systems (one located on the top floor, one in basement) or the Arzel dampers. We had just completed the plan and didn't want to change floor plan to allow for the 2 unit system. Now I am second-guessing the Arzel choice based on the potential for short-cycling. Thoughts?A lesson I learned form this:Have mechanical contractor(s) and insulator(s) in at the planning stage so you don't have to rig a sub-optimal system once the floor plan is done.
Westmich,
I would have chosen two systems, and made the changes in the floorplan to make it work.
That statement comes from someone that has experienced HVAC systems that work well... and many more that do not. My opinion may very well be different if I lacked that experience and if aesthetics was the primary concern.
In a typical residential zoned system, the equipment is operating at 100% capacity, yet the zone calling for heat or cooling requires less than that. There is no way around this simple fact unless the home is divided reasonably equally, and the equipment sized for the largest zone. Now, you have equipment that will function properly for the space being conditioned, but the equipment is not sized to condition the entire space (space as in the 2 zones added together).
Multi-stage equipment is a partial solution to the sizing for the whole house and then dividing it problem.
Newer zone systems are not 100% shutoff, so if the ducting is done right from the initial design, there is enough air bleed in the "off" side that a dump zone may not be required.
In the end, a whole bunch of stuff is being added to fix a problem that can be addressed with good design practices. Plain old solid duct runs do not break over time. Zone dampers may not be accessible in the future.
As long as it is a "plan" it can be changed. The costs of changing may very well be offset in terms of comfort and efficiency.
Danski, thanks for the reply. I can still look at the 2-unit system. The dampers were designed to be placed in an accessible spot (basement closet), so that's not an issue. I agree with what you said about proper design from the get-go.
My house is 1600 sq ft. 800 up and 800 down.The lower level is SOG. I am on a hillside and while the back of the house has a 12 ft high concrete wall it is only minimal in the ground. 4ft at the back tapering to nothing abut 1/2 around the sides and in the front the ground was built up.Yet, when I built in 1979, all of the HVAC contractors kept saying that they would stick a couple of registers in the ceiling for the "basment". Well the house does not have a basment. And I know such a design would not work.Well I finally found some one that would do something else. Ended up with 2 system side by side. One an updraft feeding the 2nd floor.The other a down draft feeding under slab ducts.My design I only installed AC on the 2nd floor and that seems to be OK.The only problem is that they installed 2 big of units. IIRC 86k BTU (inlet) on the 2nd floor and 100k on the first. Based on run times during the coldest weather I am guessing that the 2nd flr unit is 2-3 times larger than needed adn the lower 3-4 times. And the blower on the lower level is way too big, even on the slowest speed.It is time to replace that equipment. It is all, along with a WH in a closet with external combustion air inlet. I want to eliminate that.I don't think that either logistics (clearance space for external inlets and discharges) and costs will allow me to go back with a similar system, but with equipment with brings in external combustion.So I am looking at going with a sinlge furance and manual dampeners connecting to the existing duct works. Deeping on how much variation I might endup going with an automatic one.If I was doing the same house today I would do radiant heat in the 1st floor slab and hydro air for the 2nd. And again only AC on the 2nd, but with maybe a few ceiling registrers in the 1st floor to get just a bit more cooling when I have company.I like the idea of using water as the distribution method as it decouples the energy source from the loads and you can relatively easy get heat from several different sources..
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A-holes. Hey every group has to have one. And I have been elected to be the one. I should make that my tagline.
Yeah, I suppose the 86k and 100k btu units are a bit oversized, unless you leave the windows open all the time :)
My house is also on a slab, and I have toyed with retrofit radiant heat using an ultra efficient boiler and an indirectly fired water heater, but even for me at cost, it is quite expensive... Yes, I know the operational costs will be lower than what I pay for forced air, but I doubt there will ever be a return on the investment... or an increase in the value of my home.
Let's forget about undercutting the doors (or replacing them) and redoing all the floor coverings and baseboards for just a minute, too.... hee heee heee
If you want to do load calculations, go to http://www.hvac-computer.com and pay for the limited use homeowners license.
I think 95%+ efficient two stage equipment and the variable speed drive is the only way to go for conventional forced air.
We have a two-zone damper system and are happy with it.
If your view never changes you're following the wrong leader
I'm happy to get positive feedback on this--gives a guy hope.
You're in SE MN--I used to live in west WI. Great area. Big time heating and cooling extremes, so I am glad to hear about a successful damper system.
With a single unit located in your basement, don't expect much in the way of A/C on your second floor. Sure they can put registers up there, and every once in a while I even see a return installed in that situation, but the system won't work very well.
Also, I don't think that dampers work very well in controlling comfort through an entire house. Especially in a retrofit, where you are going to have to put in chases and registers where you can fit them, not necessarily the optimum location for heating and cooling. I would go with two units. It will be much more comfortable, and more efficient as well.
A great way to save money is to use equipment of appropriate size. Many hvac contractors will install larger units than necessary. If you do your own load calculations you can avoid this. Look for the program hvac-calc online, it's easy to use and well worth it IMO.