Armed Polite Society
Main Forums => The Roundtable => Topic started by: Cliffh on December 07, 2020, 11:36:50 PM
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Last spring we had the 4 ton HVAC replaced with a 5 ton unit. It was a great improvement over the summer, the AC would cool the house quickly and would keep it cool without having to run all day; it'd normally run for ~10 minutes at a time. And the electric bill went down by almost 1/3.
I'm having a bit of a problem now that it's getting colder. I like to have a fire in the fireplace in the evenings, sometimes all day if it's cold enough. Mainly the fireplace is meant to supplement the electric heater in the HVAC. The actual problem is that the new unit draws a *lot* of air. Without measurements I'd guess at just about twice what the old unit moved. Now it's pulling so much that the smoke from the fireplace is drawn into the house instead of going up the chimney. Not a good thing with two old folks who both have COPD. Not to mention setting off the smoke alarms.
I've lessened the problem by re-installing the glass doors on the fireplace and closing the flue to ~half open. Still isn't enough though.
I thought I'd pass it by y'all for ideas/possible solutions to discuss with the AC guy.
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The answer may not lie with the a/c guy. How old is your house, and are the fireplace and chimney masonry, or metal?
For a fair number of years now (I don't remember when it crept into the building codes), fireplaces have been required to have glass doors, and a duct or opening of some kind inside the firebox to admit fresh air directly to the fire so you don't suck heated air out of the house and send it up the chimney. The reason is energy conservation. Fireplaces are not a very good way to heat a house -- the fireplace only heats one room, but it pulls air back out of that room to feed the fire and then that air goes up the flue. And the warm air that goes up the flue is replaced by cold air that gets sucked into the house through cracks and loose-fitting doors and windows.
The idea behind the glass doors and the inlet duct is to make the fireplace into its own closed system. By drawing combustion air directly from outdoors, you avoid sucking heated air out of the house and replacing it with cold air.
So my suggestion would be to explore if there's a way you can create some sort of duct to bring make-up air directly to the fireplace. You should never close the damper, even part way, when there's a fire burning.
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PM sent.
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FYI: https://www.askthebuilder.com/fresh-air-intake-vents/
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In the interim, open a window in the room with the fireplace to equalize the pressure and give the fireplace some extra combustion air.
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I would have a chimney sweep company come out and check inside the chimney for restrictions etc.
Replacing the air handler shouldn't create any change in the air pressure of the house. Furnaces up to 80% or so draw air from in the house and send it up the vent pipe as well as hot water heaters also, that can create a small negative pressure inside the house. An air handler without gas heat just moves air around and shouldn't create downdrafts.
Opening the flue up all the way and cracking a window in the room with the fireplace are both good ideas. Closing the flue and starving the fire of air will both create more soot.
Did you replace your windows/doors this year? New soffits and fascia?
It sounds like your fireplace either has a restriction in the flue or is starving for combustion air.
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Your HVAC unit shouldn't be creating any draw at all unless you have a fresh air exchanger that's malfunctioning. A central HVAC system is enclosed in the housing envelope so any pressure deltas should be internal to the system, not relative to home's interior/exterior. If you turn the system on and it creates a noticeable pressure change, especially if it's enough to backdraft a fireplace chimney, something is wrong.
Brad
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The fireplace insert and chimney are both metal - basically a metal box inset into the wall with a pipe going through the roof - in a '98 double wide. It's a Coleman/Evcon 36ECMII https://www.allpartsinc.com/36-wood-burning-fireplace-36ecmii-36ecmii.html http://fmisupport.hcents.com/supportdocs/54024F.pdf
We had the original, drafty, windows replaced and a metal roof installed at approx. the same time as the new unit was installed. As mentioned earlier, the new unit sucks - there's a draft if you stand in front of the air intake - definitely more than the old one.
The glass doors are bi-fold, and there's about 1/4" gap between the each of the door panels and at the hinge sides.
I know you're not supposed to shut the flue since the gases have to have an escape path, but the smoke was already coming into the room. Closing the flue half way seemed to help in that there wasn't as much air being pulled down the chimney, across the fire and into the room.
If I've got a good fire going it seems to generate enough heat/updraft to overcome the draw from the heater. There's no problem with smoke entering the house if the heater isn't running, whether the fire's roaring or it's died down to just embers.
If I have a fresh air intake installed in the firebox, seems to me that when the fire starts dying down for the night and the heater kicks in, it'll pull air down the chimney (which is clean btw) and in though the air intake, even with the fireplace doors closed, since the doors/front of the firebox isn't air tight. If I open a window, it'll start pulling in cold air from the outside too.
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Almost forgot to mention that the heater is electric.
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If they replaced the furnace with one that will move the air the 5 ton needs yeah I can see the problem. Not to make it bad but if they didn't change duct work that is maybe good for 3-3 1/2 ton of airflow.
That single point return air would probaly suck the crome off a trailer ball.
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I don't understand how your heater works. If it's pulling air down the chimney when it runs, that means it's creating a vacuum inside the house. If it's creating a vacuum, it must be exhausting air from the house to the outdoors. Why is it exhausting the air you've just paid it to heat?
Doesn't make sense to me. If that's what it's doing, I don't think it's operating correctly.
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I don't understand how your heater works. If it's pulling air down the chimney when it runs, that means it's creating a vacuum inside the house. If it's creating a vacuum, it must be exhausting air from the house to the outdoors. Why is it exhausting the air you've just paid it to heat?
Doesn't make sense to me. If that's what it's doing, I don't think it's operating correctly.
I'm not a residential HVAC guy but I'll hazard a potential scenario.
The room with the fireplace has insufficient supply ductwork. The room has sufficiently sized return ductwork.
If the air handler for the new A/C was replaced and has a higher HP drive than the ducts were spec'd for:
The room possibly could run in a negative pressure between the fireplace combustion exhaust and higher volume return air to the airhandler compared to the volume of air supplied to the room. Other rooms would have to be in a positive pressure then I guess.
Without being there it is all speculation of course.
Regardless he needs more combustion air.
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I'm not a residential HVAC guy but I'll hazard a potential scenario.
The room with the fireplace has insufficient supply ductwork. The room has sufficiently sized return ductwork.
If the air handler for the new A/C was replaced and has a higher HP drive than the ducts were spec'd for:
The room possibly could run in a negative pressure between the fireplace combustion exhaust and higher volume return air to the airhandler compared to the volume of air supplied to the room. Other rooms would have to be in a positive pressure then I guess.
If that's what's happening, the system needs to be balanced.
Even so, there needs to be an isolated make-up air supply for the firebox if the plan is to use the fireplace. I love fireplaces, but my house was built in 1950, decades before anyone thought of making homes "tight" and providing make-up air to fireplaces. Plus, the thermostat is just outside the living room, and the entire house (a ranch, with a bedroom in the converted attic) only has one heating zone so heating the living room with the fireplace would effectively turn off the heat to the rest of the house. (Hot water baseboard heat, not forced air.)
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I would have a chimney sweep company come out and check inside the chimney for restrictions etc.
Replacing the air handler shouldn't create any change in the air pressure of the house. Furnaces up to 80% or so draw air from in the house and send it up the vent pipe as well as hot water heaters also, that can create a small negative pressure inside the house. An air handler without gas heat just moves air around and shouldn't create downdrafts.
Opening the flue up all the way and cracking a window in the room with the fireplace are both good ideas. Closing the flue and starving the fire of air will both create more soot.
Did you replace your windows/doors this year? New soffits and fascia?
It sounds like your fireplace either has a restriction in the flue or is starving for combustion air.
No need for that. Just pile a great big bunch of Christmas wrapping paper in the fireplace and light it off. That ought to burn out any restrictions. =D
(don't do that)
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Got home the evening of the 9th, opened the laptop & received a message basically saying "I'm broke so bad you've got to take me to the repair shop". Picked it, (and the broken HDD), up this morning - on the way home from the hospital where my surgery had been canceled. (grumble) Got up early, skipped breakfast, drove 1 1/2 hours, only to be sent home 'cause the doc was "busy with a trauma patient" (/grumble)
Had a chat with Nick1911 where we determined that what's most likely happening is there's not enough air coming out of the floor registers to supply the air demands of the heater. A couple possible reasons are that the supply ducting is way too small (my idea) or there's a leak in the supply ducting (Nick's idea, most likely the correct answer).
DW talked with the AC installer, his idea was that there's a problem with the chimney - that the chimney was blocked, not letting the exhaust out and it would backup into the room. He recommended a chimney sweep, she called and made the appointment. I talked with the sweep when he called to confirm, he didn't seem to hear me when I mentioned that when the heater's running you can feel the cold air coming out of the fireplace even when the fire's out, the damper's closed and the doors are shut.
The chimney is now clean, and we're still having the same problem.
The sweeps' suggestions were to a) don't use the fireplace b) open a hole in the wall to feed air into the room and/or c) open a window near the air return.
Inspecting the ducting would be a serious pain in the ass. It runs under the house, with about 6" of fiberglass insulation held in place by underbelly wrap (basically a tarp) covering the entire underside of the house. I am not in any shape for tearing all that apart.
Next step will be calling around to see if there's an HVAC company around who can inspect the ducting, preferably with a camera.
Today we just shut off the heater & used the fireplace, we'll reverse that tonight.
ETA: I did a quick & dirty test on the air flow from the floor registers. Turned on the house fan and held a few squares of TP over each register. The house is a rectangle, there are two supply lines running lengthwise, one on either side of center-line of the house. The registers on the rear side of center-line are definitely putting out more air than the others.
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One other suggestion had been to throttle back the air intake by blocking it with "something". Not sure I like that "fix" either, seems as if it'd put more of a strain on the motor.
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Does each room have a return register or is there a single return register (usually in a hallway)?
Do you have any rooms you rarely or never use where you might be able to close the supply registers?
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All of the rooms have a floor register (outlet), including the bathrooms. There's one intake for the HVAC, located directly above the unit, which is in the laundry room at one end of the house.
There are a couple of rooms we normally keep the doors to closed. I don't know that closing the registers would allow more air to circulate through the house, seems as if it'd put more back-pressure on the system and potentially force more air out of any leaks in the ducting.
Thinking about the closed doors, the air supplied to those rooms can only exit those rooms through the small space under the doors. That right there is going to cut back on the amount of air available to the intake, and will have be made up from another source - such as the chimney. We'll have to run an experiment.
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You're right. I know it's noisy but leaving the laundry room door open will also help.
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And you're right too - it is noisy. We rarely close that door. The builder did take into account that someone might want to close that door while the unit's running, he/they put a grill in the lower part of the door that's the same size as the grill on the air intake for the unit.
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Not to hijack the thread, but is there something wrong with closing the door where the HVAC is? Mine is in the laundry room as well and I always close that door at night since it's next to my bedroom and I don't want the extra noise at night. I don't have any kind of vent in the door.
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Where the unit is is less important then where the air return is.
Does your air handler have a ducted return, or does it just suck in from one end of the unit?
Mine is in the garage, and the returns are ducted to pull from the house.
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Where the unit is is less important then where the air return is.
Does your air handler have a ducted return, or does it just suck in from one end of the unit?
Mine is in the garage, and the returns are ducted to pull from the house.
I don't completely understand my system. It is a dual system - heat pump for heat and cooling, and propane furnace for heating at below 26deg. When I bought the place, it was set up so there was a register with filter in the living room ceiling, a register with filter in the upstairs bonus room, ans a smaller register in a hallway connecting the two back bedrooms.
That system crapped out, and the new one has extra large ducting coming down from the ceiling to the furnace unit (but filtering for the heat pump as well) with one of those ginormous 8" thick air filters. They removed the filters from the LR and bonus room registers and told me to leave it that way. I hear air being pulled from those registers, and there is no obvious place, like a register, for "air in" in the laundry room.
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You are ok closing the door. The other unit just sucks through the door when it is closed.
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I don't completely understand my system. It is a dual system - heat pump for heat and cooling, and propane furnace for heating at below 26deg. When I bought the place, it was set up so there was a register with filter in the living room ceiling, a register with filter in the upstairs bonus room, ans a smaller register in a hallway connecting the two back bedrooms.
That system crapped out, and the new one has extra large ducting coming down from the ceiling to the furnace unit (but filtering for the heat pump as well) with one of those ginormous 8" thick air filters. They removed the filters from the LR and bonus room registers and told me to leave it that way. I hear air being pulled from those registers, and there is no obvious place, like a register, for "air in" in the laundry room.
Your description seems to be incomplete. Do you have ducted supply and free return, ducted return but free supply (highly unlijkely), or both supply and return ducted?
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All of the rooms have a floor register (outlet), including the bathrooms. There's one intake for the HVAC, located directly above the unit, which is in the laundry room at one end of the house.
There are a couple of rooms we normally keep the doors to closed. I don't know that closing the registers would allow more air to circulate through the house, seems as if it'd put more back-pressure on the system and potentially force more air out of any leaks in the ducting.
Thinking about the closed doors, the air supplied to those rooms can only exit those rooms through the small space under the doors. That right there is going to cut back on the amount of air available to the intake, and will have be made up from another source - such as the chimney. We'll have to run an experiment.
Ironically, I was thinking that by restricting flow into unused rooms it might increase the systems static pressure and push more air into the room where you need it the most (fireplace room). If you are keeping some spare room doors closed you are for all practical purposes doing that already.
So my idea was not only wrong but in fact might be if not the main cause, at least a contributing factor to your problem.
Keep all the spare room doors open and make sure all the supply registers are fully open, see if that changes anything.
Ultimately though, you are sending air up through the chimney stack and out of the house.
That air has to be replaced from someplace. If your house is real tight there will be no way to make up the air being sent out the chimney. That's a recipe for venting problems.
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Ironically, I was thinking that by restricting flow into unused rooms it might increase the systems static pressure and push more air into the room where you need it the most (fireplace room). If you are keeping some spare room doors closed you are for all practical purposes doing that already.
So my idea was not only wrong but in fact might be if not the main cause, at least a contributing factor to your problem.
Keep all the spare room doors open and make sure all the supply registers are fully open, see if that changes anything.
Ultimately though, you are sending air up through the chimney stack and out of the house.
That air has to be replaced from someplace. If your house is real tight there will be no way to make up the air being sent out the chimney. That's a recipe for venting problems.
In tight houses, fireplaces simply don't work, because after a short time there isn't enough air to send up the chimney due to the lower pressure iside the envelope compared to outdoors. This leads to smokey fireplaces and CO2 (or CO) contamination. That's why the building codes have, for a number of years, required a dedicated make-up air duct or opening to feed combustion air directly into the firebox.
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Went to bed last night with the heater running & set at 72*. Woke up this morning with the heater still running and the thermostat reading 68*. Started checking the various registers, a couple had good airflow, some had very little. Strange thing is that one of the registers with good airflow is also the one that's furthest away from the unit. Put in another call to the original AC installer, I'll try describing the situation in different terms when he shows Monday.
I hadn't thought of the air loss through the chimney due to the fire/heat, and that having to be made up somehow. That may end up being another problem once we get the (likely) duct problem fixed. This old place isn't all that tight - it is tighter than it used to be - so there may be enough incoming through other leaks that it won't have to draw from the chimney. Although it may still draw from the chimney once the fire starts dying. Then again, there shouldn't be as much loss up the chimney once there's not as much heat... Then again, it'll most likely draw from the area with the least resistance, which may end up being the chimney.....
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Went to bed last night with the heater running & set at 72*. Woke up this morning with the heater still running and the thermostat reading 68*. Started checking the various registers, a couple had good airflow, some had very little. Strange thing is that one of the registers with good airflow is also the one that's furthest away from the unit. Put in another call to the original AC installer, I'll try describing the situation in different terms when he shows Monday.
I hadn't thought of the air loss through the chimney due to the fire/heat, and that having to be made up somehow. That may end up being another problem once we get the (likely) duct problem fixed. This old place isn't all that tight - it is tighter than it used to be - so there may be enough incoming through other leaks that it won't have to draw from the chimney. Although it may still draw from the chimney once the fire starts dying. Then again, there shouldn't be as much loss up the chimney once there's not as much heat... Then again, it'll most likely draw from the area with the least resistance, which may end up being the chimney.....
You still haven't (IMHO) adequately described your heating system. Start with the basics -- ignore the fireplace and chimney, as if there's no fire and the damper is closed. How does the heating system work? Unless it's a fairly modern system that continually exhausts a percentage of warm air and brings in a corresponding amount of fresh, outdoor air to avoid "sick building syndrome," it should be a closed system. All it's doing is pushing air through the ducts and registers from one part of the house to another. As such, it's balanced. A closed system is always balanced. You can change the amount of heat one room gets compared to another by opening and partially closing registers, but the overall system is just pushing air around inside a closed box.
Now you open the damper and light a fire. The fire needs air to burn, and the hot air from the fire goes up the chimney and is exhausted. That air has to be replaced. In leaky old houses, the replacement air sneaked in through cracks around doors and windows. The term for this is "infiltration." Because you're sending heated air up the chimney and replacing it with cold, outdoor air, it wastes energy. That's why the building codes changed to mandate glass doors and make-up air inlets for the firebox. That allows the fire to pull air from outdoors to use as combustion air rather than using the air you already paid to have heated by the furnace. By using glass doors to separate the firebox from the house, you allow (in theory) the house to remain a closed, balanced system while the fireplace and chimney operate as a separate, flow-though system.
The question is why your heating system isn't functioning as a closed system.
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It's a closed system as you described above, it's not designed to bring in outside air on purpose.
Right now, my money's on a leak in the ducting. The closed system isn't - it's loosing air somewhere. The fan's drawing the air from the house, pushing it out into the ducting, the air is not coming back into the house from the ducting (evidenced by the low/lack of flow at too many registers) - causing the need for supplemental air to be drawn in through *something*.
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I agree. If the system didn't have a leak it really couldn't pull air down the chimney.
The good news is that you don't have to worry about pipes freezing in the crawlspace. >:D
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I agree. If the system didn't have a leak it really couldn't pull air down the chimney.
The good news is that you don't have to worry about pipes freezing in the crawlspace. >:D
Sure is looking that way.
Trying to fix things over the phone or internet frequently doesn't work out well.
Hopefully the probable causes have been narrowed down.
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Discussing the problem here (and with Nick1911) has narrowed the probable causes & given me a direction to point the repair guys.
And pointed out I may have to do something about a fresh air intake for the fireplace.
Yeah, the pipes aren't going to freeze - if I can afford to keep heating the crawlspace. :'( :)
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The HVAC guy just left with my check. I could have fixed it myself, but a) he was here b) it didn't cost all that much and c) I'm getting too old & broken to be working overhead under the house if I don't absolutely have to.
There are two main runs to the 12" ducting paralleling the long walls and a couple of feet to either side of center-line. There's a 12" flexible cross-over connecting the two main runs. The crossover had come loose from one run.
I'll bet the critters under the house appreciated the heat.
Since it's projected to be too warm the next couple of nights to test the fireplace with the heater running I may just turn the fan on with a fire going and see what happens.