OK this is probably going to get long but here goes.
New boiler put in 3 years ago. House is only about 1500 Sq. ft. English colonial built 1935 near Boston MA. Presently no insulation in walls (plaster). Heat is forced hot water, gravity system converted to forced hot water with 1 zone and circulator when the burner was replaced.
Concern is the boiler room venting (I enclosed it during a basement remodel last year) and overall air quality. Boiler Room is about 11 ft. by 7 ft. and also contains a gas water heater, Furnace is oil. No venting presently but there is a window which could be used to get outside air.
I recently had a home energy audit done and I can get the walls insulated (blown in cellulose) through Nstar contractors for about $2100, estimated savings $400/yr. Nstar also has a rebate program which will rebate 50% of the $2100. So it seems like a no brainer. Attic in the house has about 6 inches of fiberglass unfortunately under a tongue and groove floor (so additional insulation there is a major project) This is also my only storage space as I don’t have a garage. I may go ahead and foam the roof as well given the floor insulation situation up there.
Now the issues. As I’m tightening up the building I’m getting more concerned about combustion air in the basement and indoor air quality overall. During the energy audit they checked the boiler and hot water tank for CO and efficiency, Neither was a problem for CO and the oil burner was running at 86%. I still want to make sure under a constant load and when running more often the boiler is running properly. Last year when I asked the boiler technician about the venting issue he said well let’s see how things work and we can address it if there is a problem (Ahh not the response I was looking for). I’ve switched companies this year and haven’t had anyone in yet from the new place. So before I do.
Questions what is the proper way to ventilate this boiler room as well as the rest of the house? I’ve looked at some ERV and HRV (Aprilaire) units but it seems everything is geared towards a house with a central air setup, forced hot air or installing ductwork throughout the entire house which is not an option (we’re not talking a lot of open closets or wasted space to run new ducts). I figure I could install a unit in the attic for the upstairs bedrooms (in fact we’ve considered this for central air in the future) but there is no way to get the same unit to ventilate the first floor never mind the basement without ripping out walls and such which ain’t going to happen.
so what kind of alternatives do I have? Anyone have any great ideas because I’m really at a loss on this one
Replies
Ribs,
First, let's talk about vocabulary. When one speaks of venting (in reference to a boiler or a water heater), one usually means the venting of exhaust gases through a chimney or flue. It seems that you're talking about something else -- usually referred to as providing combustion makeup air (that is, fresh outdoor air used for combustion). You may well be correct that your boiler and water heater need better provision of combustion makeup air. The trend in the industry is toward sealed combustion units that have ducted combustion air from the exterior.
Secondly, you should know that neither an HRV nor an ERV is intended as a source of combustion makeup air. They provide fresh ventilation air, not combustion air. Manufacturers of HRVs and ERVs specificially note that the units are not intended to provide combustion makeup air. They are balanced units -- that is, just as much air is drawn into the house as is exhausted from the house -- and therefore cannot and should not be used to provide necessary combustion makeup air.
Edited 10/18/2006 9:35 am ET by MartinHolladay
Thanks Martin, I was pretty clear on the terms though not on the use of the HRVERV units. I guess my post was not clear on any of it. I pretty much knew ERVHRV was a balanced unit but I would have thought that combustion air was part of the balanced equation.Thanks for clarifying.Ribs
Edited 10/18/2006 9:50 am ET by Ribs
A 4" piece of pvc from outside the house terminating near the burner on your boiler and water heater will do the trick. Less than $100 - solved.
The windward side of the house would be the best location for the other end of the duct, and should be covered with a screen to keep the critters out.
Your appliances will benefit from denser, cool air, and will not depressurize the mechanical room.
As for the living areas:
If your house is super tight (difficult on a retro unless you spray foam, and well) you may need an ERV/HRV. But I personally would wait and see if your humidity levels rise - it may not be an issue.
Brian,
As Tim's example makes clear, your solution (4" round duct to supply combustion makeup air) would almost certainly be undersized. This is not a good example of a situation where guesswork is a good idea. Years ago, an architect I know designed a mechanical room with insufficient combustion makeup air for a three-unit apartment building. The owners discovered there was a problem after CO detectors were installed in the apartments upstairs. All the alarms went off, the fire department showed up. Sure enough, there was a problem.
Martin - Thanks for your concern, and perhaps my response came off as flippant. I like Tim's post - the window is already there, and certainly adequately sized - its an elegant solution, though mechanical and not a simple as a dedicated duct.
And its not that clear. The 1" clear opening per 1,000 btu is for connection to inside air space in a house with a discontinuous vapor barrier. The inside space may include several rooms if connected with high and low openings, with each opening providing one square inch of clear opening per 1,000 btu/hr input rating, but not less than 100 square inches each.
Direct outside makeup air is a different animal - the (requirement drops by a third, or a quarter if any inside air is involved) and we'd need to know the btu ratings of both appliances for the times they would fire together. The flue outlet sizing would help too. (See the attached worksheet)
Additionally, the house will be retro insulated with cellulose, and a blower door test will be the only way to tell, but it will be very difficult to seal the house tightly. The insulation will be better - air infiltration...I'm not so sure - 38% reduction in air infiltration is what one manufacturer claims - but the older the house, the more problematic. Even with a world-class cellulose job, he'll likely not suffer depressurization issues.
Before I did anything, I'd have a $50 CO detector plugged in somewhere - in any house with fuel powered equipment.
My Bock Oil Fired Water Heater has a 4" makeup air inlet, and a 4" flue. This was engineered at the factory, and its a 126K BTU unit. But I'm in an ICF house, so infiltration is minimal.
I imagine adding any makeup air, in the OP's situation, would be a "belt and suspenders" approach, and a good idea.Treat every person you meet like you will know them the rest of your life - you just might!
The reason I specifcally listed the Codes that require the configuration that I suggested was to hopefully prevent any confusion with a conflicting code such as the UDC. Frankly, I have never heard of this code. If this is the code that apples where you live and work, you have my condolences. It seems, from the worksheet you attached, cumbersome. OTOH, the International Mechanical and International Fuel Gas codes are basically reiterations of the NFPA code requirements for the same type of installations, and is widely accepted accross the country.
So to be very clear, the 1 square inch per 1000 btu/hr of rated input is for direct supplied outside air to a mechanical room. The requirement that combustion air be provided by mechanical or gravity means is predicated on the "confined space" and "unusually tight" definitions contained within those codes.
Comparing the venting configuration of a sealed combustion, draft induced appliance to a natural draft appliance with gravity combustiuon air supply is to compare apples to oranges. One is very different from the other. Mistaking that difference could create an unsafe situation.
Comparing the venting configuration of a sealed combustion, draft induced appliance to a natural draft appliance with gravity combustiuon air supply is to compare apples to oranges. One is very different from the other. Mistaking that difference could create an unsafe situation.
Sure - I thought of that, but I forgot to include it. My unit is not power vented, however, but the ducting goes directly to the intake.
I find it unusual that codes vary by a factor of three, and would choose the more generous figures to err on the side of safety.
From the OP's description of his house, it sounds like he is headed in a good direction - I hope he takes your advice, especially if his room is well sealed.
Treat every person you meet like you will know them the rest of your life - you just might!
"... unusual that codes vary by a factor ...."
I do business in sevaral midwestern states, and the differences from place to place and state to state, can be staggering. Some codes are extreme overkill, some are just barely good enough. Some make no sense at all. For instance, the building codes in the city of Chicago seem to be soley for the enrichment of the local unions that rule the place, rather than concerned with the health and well being of the citizens.
First, combustion air supply and general ventilation (i.e. fresh air for air quality in the living spaces) must be treated separately. An HRV/ERV for general ventilation is always a good idea. 200 cfm will give you 1 air change per hour (ACH) and will provide all the fresh air you will need.
You said that you have a window that opens directly into your mechancial room, right? The best way to provide combustion air into a confined space would be to use the window, fit it with some duct and a motorized damper. The International Mechanical Code and The International Fuel Gas Code both require 1 sq inch of opening per 1000 btu/hr (for both appliances) of input. Say your boiler if 75K and your WH is 40 K, that is 115 sq in required. That could be done with a 16x8. A 24v, spring return motorized damper is readily available from Honeywell and DuroDyne. You would need simple controls to open the damper whenever the WH or the Boiler were firing. You mention a furnace. I assume you mean your boiler. As you tighten the house, you can create a condition where the inleakage is reduced to the point (I don't know what exhausts you have) that you could back draft (the WH and boiler have no power vents, right?) either WH (more likely) or the boiler (less likely, but possible). The manner I suggest is "by the book" with the addition of the requirement that there be two openings, one within a foot of the ceiling and one within a foot of the floor. Usually the jacket and piping heat losses are more than enough to keep the room from freezing, but it is a concern, especially if the damper sticks open.
Thanks Tim, those numbers from the code are exactly the type of thing I was looking for. I plan to have the new service guy in from the new oil company and wanted to ask him about the equipment you mention from Honeywell and durodyne (I had a quick look on line and couldn't find them). I'm guessing he will know how to hook it up so it opens when the boiler or WH fire (although based on the last guy won't count on it).Yes when I said furnace I meant boiler. No neither the WH nor the boiler are powervented. You said "The manner I suggest is "by the book" with the addition of the requirement that there be two openings, one within a foot of the ceiling and one within a foot of the floor." Do you mean the these two openings are in addition to the 1 sq inch of opening per 1000 btu/hr (for both appliances)? I found what I think is a good diagram of this but don't really understand the use of the ventilation air? It looks like the 1 inch/1000btu/hr is combustion air and the other two openings are for ventilating the utility room. Why do this if the units are not putting out any CO (all going up the chimney)?My sister had her house done last year by a contractor and fully inspected. They have two registers about 6 inches by 10 in the wall into the living space and were told that was sufficient (I'm guessing these are for ventilation). No allowance at all for combustion air besides that.Thanks again
What I meant by the two openings is an "expansion" of the requirement of 1" per 1000 btuh. In other words, if you take my example, you would provide the 16x8 (min) opening into the space, using a duct with two openings in it, one near the floor and one near the ceiling. Each opening in the duct would be full size, 16x8.
In a mechanical room of the size and equipment that you have in your house, providing the code required combustion air will suffice for any ventilation requirements as well. In a large commercial mechanical room, an additional 0.05 cfm/ft2 is required. Usually using outside air for cooling far exceeds the requirement.
If you look here http://www.durodyne.com/products/durozone/durozone.pdf you can see the catalog that has the dampers in it.
Edited 10/18/2006 10:35 am by Tim
Great thread. Wonder what current thoughts are. I’m in the process of tightening up my house. Unfortunately because of COVID, blower tests aren’t allowed in my area at the moment. So I have no idea how tight the house will be.
My primary heat is a Mitsubishi Hyper Heat multi zone ductless system. I usually run a Peerless oil fired boiler as a secondary system in the basement. It has a 6” duct exiting to flue into chimney. There is a window in the room, but I cringe thinking of letting all that cold air in.
What if I were to run an HRV just for the basement with positive pressure and supply fresh air to the utility room, or is there a way to have the HRV go into boost mode when the boiler is firing? Still a no no?