Hello all,

Brand new to the forum and hoping for some advice. I came across this while searching for info and some of the responses that I saw posted to all were outstanding so I didn't hesitate to join (normally remiss about signing up).

Anyway, my current system is a Trane XE 80 forced air gas furnace that is tapped into old duct work, some of which is the old convection type for fireplaces/wood burning stoves in the basement (house was built in 1910 or so). The system has a Honeywell electrostatic filter, and I had the house insulated (blown in cellulose), and windows are relatively new (vinyl, double pane). Also, the kitchens and bathrooms have no heating (mother/daughter setup). I am looking to upgrade my system with the following goals/concerns:

Concerns (in random order):
- air is very dry
- temperature, while better than before insulation, still fluctuates too much
- two of my three kids have asthma, and allergens are a high concern
- have lived in the house 8 years, and not sure how old the system was when I moved - may be overly inefficient

Goals (also random):
- increased comfort/more stable temperature
- improved air quality/RH level
- add central cooling
- reduce energy use/ongoing costs (willing to absorb higher initial costs if the break-even point is reasonable)
- add heating to kitchen/bathrooms (something hopefully more cost effective than electric radiant to all three bathrooms)

I have been examining options and doing some research (how I came across this site) and have considered the following options:
- balance system, add registers, add system humidifier
- upgrade furnace
- add compressor, keep furnace
- add compressor, upgrade furnace
- add heat pump, keep furnace
- add heat pump, upgrade furnace

Any advice/guidance would be appreciated. I am starting to do my HW, but have no prior experience nor training on this.

Thanks,
Eddie

 

This is very involved and so before I write ten thousand words I want to make sure that you return. I'll ask one question and make one request.

Do the supply ducts from the existing furnace exit into the rooms on the outside walls or on inside walls?

Can you take some pictures of the existing furnace and ductwork and post them? I don't need any close-ups, just pictures from far enough away to get a general idea of how it is laid out.

 

Thanks for the reply Furd, and completely understand where you're coming from. I figured that I'd put it all out there to give as complete a picture as I could.

The ductwork is all in interior wall space and is optimized for heating (all registers are in the floor). I'll take some pictures and post those, but that'll have to wait until tonight at the earliest.

 

How many floors does the house have? How big are they? How many rooms on each floor? Are all the walls plaster?

 

Hi Eddie,
I'll key in on your "dry air" concerns. Forced hot air is often blamed for the resulting dry air, but the problem related to air leakage, sometimes made worse by poor air ducting. In addition, your desire to improve your air quality is affected by this air leakage. Here are some numbers.

When we air seal a house there is a limit where if we get too tight we must add a source of fresh air. That limit is generally considered to be 0.35 air changes PER HOUR. An air change is the entire volume of your home. At 0.35 that would mean a home is replacing all of its inside air every 3 hours. But, at that rate a home usually doesn't have dry air. That means your home is probably replacing all of the inside air every 2 hours.

I admit that when I first started doing energy audits several years ago I thought those numbers were ridiculous. But after conducting many blower door tests and seeing the difference between a tight home and a leaky home, I now understand the importance of air sealing and controlling the the air we breathe.

Go crazy air sealing and the obvious required insulation and you can probably eliminate the humidifier along with reducing your heating/cooling costs. Balance the remaining air needs with a powered ventilation system where you can filter that incoming air and your indoor air quality will greatly improve.

As Furd said, much more to come so I'll add a link on air sealing and add more as we get more details. And you are correct, this IS a great forum. I credit myself with only a tiny area of expertise and come her often to get my questions on many topics answered.
http://www.efficiencyvermont.com/ste...ide_062507.pdf

Bud

 

Pulpo, the house is a village colonial and the layout is:

• ~1,000SF basement (5 rooms - kitchen, bathroom, den, bedroom, HVAC room)
• ~1,000SF first floor (5 rooms - kitchen, bathroom, dining room, family room, living room)
• ~1,000SF second floor (6 rooms - bathroom, four bedrooms, nursery)
• ~700SF unconditioned attic

Walls are plaster, covered by gypsum. I'm not sure what condition the plaster is in since it was covered by the previous owner.

Bud, thanks for the thorough reply and link. I'll have to process the information more - a bit unclear atm. I had an energy audit done a couple of years ago resulting in a project to air seal and insulate the house. After the work was completed, the contractor ran the blower door test again and the change in leakage was substantial enough to qualify the project under NYSERDA guidelines for ROI (just barely made the leakage criteria).

 

Unfortunately many targeted air sealing programs only hit the quick and easy leaks and only need to reach that 0.35 mark I mentioned. I'll assume you have different groups living on each level, but maybe not, just built that way. In terms of air flow, the top floor is breathing a lot of exhaled air from the people below. Fresh air pushes in the lower floors, up through the building where it becomes no longer fresh, and out the upper leaks. With three different levels you might want to think about zoning the heating system and providing isolated air exchange.

The first actually tight home I worked at was an eye opener. The owner was addressing condensation on the windows in the winter. And that was while running 2 dehumidifiers. Once a home becomes tighter than 0.2 (or there about) the moisture contributed by the people and their activity will exceed the total required. Cold winter air, once heated to indoor temps, is usually below 10% to 15% RH, sometimes lower.

An ideal home of the future will condition (temp, moisture, and other pollutants) all outside air before it is introduced into our living space. It will also be conditioning the indoor air to remove the pollutants we and the things we own generate. Not going to happen today, but it gives you a target.

Do you recall the before and after blower door measurements?

Bud

 

I don't recall the blower measurements, but can probably find them in the report I received or get them from my contractor. As far as occupancy, up until early this year, I had tenants in an apartment basement, and my family used the remaining space. We are now incorporating the basement space for my family's use and it will be only us throughout.

Thanks for the clarification - now I get it. It may be tough to really get my house tight, but it's good to get a better handle on how much that influences comfort and how high the bar is.

 

The reason I asked the size of the house was that I thought it might be a good idea to convert to a hot water system or at least install one as a supplement. It could very well help the asthma problem, that your children have. That comes first.

 

My first consideration was to eliminate the furnace and install a tank-less, baseboard hydronic system. This would be easy in the basement and first floor (basement ceiling is exposed, but would be quite a project upstairs. Initial quotes that I received were close to $20K, and this would not include any cooling. We currently have window units, and my wife would like to eliminate those and go with central AC.

I also considered some kind of hydronic/mini-split system, but it doesn't seem efficient for my area. The heat pumps would do fine cooling, but it gets too cold here to pull sufficient heat out of the air efficiently.

 

That your ductwork is backwards is a huge deal, at least for me. By backwards I mean that since at least the 1940s heating engineers have followed a concept know as perimeter heater where the heat is introduced at the point of greatest heat loss. In simple terms this means that the supply registers should be located under the windows in the outside walls. By using perimeter heating you minimize the temperature differentials between the outside walls and the center of the room. Obviously this also means that return air ducts need to be installed in the interior of the house.

So, if you want maximum benefits then you are going to need to replace all the ductwork.

Bud has made excellent comments on air sealing; one hundred years ago houses were purposely made "leaky" from an air exchange stand point. There were two "reasons" for this construction, the first is that fuel was cheap and the second was the popular thinking at the time that most medical problems were caused by breathing "stale" air. In line with this the furnace was oversized, often vastly so, to make up for the inherent inefficiencies of the furnace itself and the much higher heating requirements of the house. With only a minimum amount of air sealing and insulation retrofitting is highly likely that a heating system of only one-third the BTU rating of the existing furnace would be adequate.

Pulpo's suggestion of going with a hydronic heating system is a good one, albeit just as expensive as replacing the existing ductwork and without any additional benefit of cooling. It is always easier to install piping than it is to install ducts. Having lived with (and designed/installed) both forced air and forced water systems I would always prefer the hydronic solution for new construction, especially if heating was the priority and the cooling would see minimal usage. Another downside of a hydronic system is that it offers no controlled air movement, no control of indoor relative humidity and no cleaning of the air.

Now, the very first thing you need to do is what is called a "Manual J" (manual as in handbook) heat loss/heat gain calculation on the home as it is. This will determine how big a heating (and/or cooling) system you need based upon the present construction of the house in its geographical location. From this you can then "plug in" various improvements in insulation and air sealing as well as improvements in windows and doors to see the net savings from making these improvements. There are numerous iterations of the Manual J process, the most conclusive being the full method as described by ASHRAE, the American Society of Heating, Refrigeration and Air conditioning Engineers. Doing the calculation manually is quite tedious and prone to mistakes in arithmetic so there are many computer programs that make the task easier. There are also many "quick and dirty" calculators on the Internet that offer free results. Unfortunately, as in all things, the price you pay is often very important regarding the results you receive. In other words, the free calculators will give usable, but generally poorer results than a fee-based program.

 

Furd,

The ductwork is set correctly on the main level, but is backwards as you describe on the upper floor. Changing this would be a nightmare, and might require building chases that would not be very aesthetically pleasing. Thus, I think I'm going to have to live with that and may just have to oversize the system to compensate.

My current furnace is 100,000 BTU's, and I'm not sure how large would be needed, but I started poking around with the Manual J calc's. I expect that a good contractor would run this analysis and I can use a quick web tool as a double check.

I went through Bud's (thanks again for the link) recommended pdf, and noticed that everything applicable was done at my home. The only areas that presented, and continue to present a challenge are the pocket doors. The contractor recommended sealing these up permanently, or perhaps replacing with French doors. In the end, we used some very wide clear tape that we put in place over the winter months.

I took some pictures of the system as you requested, but am having trouble uploading... will have to give it another try later.

 

I dug up the report from my insulation/air sealing contractor and it states that infiltration was originally 5,600CFM@50pa and final results were 3,000CFM@50pa. I'm not sure how this translates into the numbers that Bud mentioned. The house is approximately 28K CF of heated space.

Also, had a second HVAC contractor come take a look at the system and he suggested installing three zones (one for each heated/cooled space). I'm still waiting on pricing.

Nonetheless, it looks like the project is growing exponentially - carpentry, electrical and plumbing issues, as well as, some modifications to bring the space up to current codes. The HVAC may have to wait until next year - which may be a blessing in disguise as it'll give me more time to research options.

 

Here's my second attempt at posting the pictures...

 

Hi eddie, just to follow up on my dry air concerns, your current blower door test of 3,000 cfm at -50 pascals for a volume of 28,000 ft³ converts to approximately 0.32 ACHn (air changes per hour naturally) and that is as I suggested the typical target range they shoot for to avoid the need for mechanical ventilation. But knowing that number tells us your dry air is probably not from air leakage.

But it most likely is from air exchange as there is nothing inside your home that is removing moisture, unless you are running an air conditioner or dehumidifier. The next possible cause of air loss goes right back to Furd's concerns about the ducting. When your blower turns on, a properly designed system will avoid pressurizing or depressurizing different area of the house. Those unwanted unbalanced pressures will force good air out and pull bad air back in. The energy auditor type people can do some duct leakage testing to help identify if this is a problem. The shotgun approach is to double check all ducts for leaks and of course have the system balanced.

Bud

 

Thanks Bud. It's good to hear the air leakage is not the issue that I was beginning to suspect (it is likely even better than 0.32 ACHn since I estimated on the high side for conditioned volume); it would have been very disappointing had this not been resolved after the extensive work that was done. I'll have the energy auditors perform that duct leakage test you recommend.

I suspect that the ductwork is a big part of the problem. The system looks pieced together haphazardly, with excessive bends/constrictions, and with a lot of tape used. I've looked at pictures online of new systems and everything is neat and unobstructed - quite different than what my system looks like.

 

I am curious about one thing - Since the furnace is not direct vent how does that factor into the air change number?

 

When a naturally drafted furnace is running it is acting like a bath fan, exhausting inside air and requiring the building leakage to provide the makeup air. So at first glance it looks like it is working in our favor. However, furnaces only run when it is cold outside and during that time the temperature difference driving the stack effect is strong so the house doesn't really need the boost.

As for the air change number itself, all mechanical fans are off and that number reflects just the house leakage. Unfortunately, when you get into the details, the 0.35 ACHn number (Air Changes per Hour natural) has so many approximations getting to that number that it is difficult to even call it an estimate, but we need a number with which to move forward so we use it.

Bud

 

100k is big for 2000 sq ft unless not insulated.

How is your house built? Double brick? framed? is there any insulation in the walls or attic?

Oversizing will not compensate for lousy ductwork. Your ductwork, even at the furnace is a total mess and will have to be torn out and re-done. Proper trunk lines will have to be installed.

Central cooling will not work well on the second floor with gravity-feed ductwork - the grills aren't designed to throw the air up towards the ceiling and there's probably a lot of leakage.

 

The house is balloon framing with blown in cellulose insulation in the attic and walls. Cantilevered floor over porch is blocked off and has foam insulation, and there is foam insulation around the basement cove.

Since the duct work is a mess, and since it wouldn't work well for cooling, does it make sense to go with a completely different system? I'm back to considering a hydronic system for heating and perhaps a mini-split for cooling and supplemental heating, or hydronic for heating and compressor with attic duct work for cooling to the bedrooms and upper floor (allowing natural flow to cool the lower floors).

Am I being foolish for considering two systems instead of an integrated system that both cools and heats?

 

Not at all! It was a month ago that I suggested a hot water heating system. The cooling can be a separate system & it shouldn't be a problem.

 

If your insulation was done properly, you shouldn't need a 100k furnace. You would be far more comfortable with a 60-80k.

A load calculation needs to be done, hopefully room by room so duct issues can be corrected.

As for doing two systems, it's far more expensive and high efficiency furnaces are far cheaper than high efficiency boilers, both to buy and repair. Best thing you can do it fix the system.

Cooling can be done with changes to the ductwork; do not rule out running new ducts to the second floor. It may seem like a pain, but it may not be as bad as you think if there are partition walls to go through.

The ductwork in your furnace room can be re-done when they change the furnace.

Is your basement finished? If not, could we have more pictures of the ductwork?

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Contractors do want to get in and out quickly and make a quick buck, so you will get the runaround. Consider consulting someone (like a designer) who doesn't have a vested interest in selling you a machine.