Hello all. Before I speak to the HVAC installer about this potential problem, I wanted to get possible insight first.
We had a fresh air ventillator (ERV in this case) installed in our house in Connecticut. Our house has an air handler for each floor and the ERV is connected to the upstairs air handler which sits in our insulated attic (We have icynene in the rafters so the attic is in the thermal envelope). The ERV is programmed to run 4 times a day for an hour each time.
Our issue is that the upstairs is much colder than before the system was installed. The system has to run longer to achieve the desired temperature and even then there are cold spots around the vents. I understand that while the system is running the cold air mixes with the return air so it will be cool especially when the outside temps are in the 20s. The issue I see is that even when the ERV is not running, the air coming in from the vents is very cool. So much so that I believe the upstairs is being heated by the downstairs system.
My question is whether there should be some type of damper installed that prevents the cold air from outside into the air handler when the ERV is not running? For giggles, I was thinking of disconnecting the ductwork connecting into the air handler to see what difference it makes but wanted to check to see if anyone had any real insight into how this should be installed.
Again, I will be contacting the installer but wanted to have other facts and opinions in my back pocket first.
Thank you
Replies
It kind of sounds like there's an air leak to the outside elsewhere in the house (possibly in the supply side downstairs) and you're drawing a vacuum in the house. Or possibly an un-closed fireplace damper.
It will be interesting to see what someone that knows these systems well says but it sounds to me like your HRV is not working properly. Is there a way you can disable and isolate it for diagnosis. Sounds like the cold air is moving downward from you above, and your 1st floor is warm so it seems unlikely a basement air leak would cause your problem. It doesn't seem like the ERV should cause a pressure change in your house if its working properly.
Do you know if there's an air flap on the ERV's exhaust the outside to prevent backflow? Maybe that is hanging open? I'd dive in and take some things apart.
"Do you know if there's an air flap on the ERV's exhaust the outside to prevent backflow? Maybe that is hanging open? I'd dive in and take some things apart."
That was how I was going to approach it so we're on the same page.
I am as certain as can be that cold air is not being drawn if from downstairs. The 2nd floor area that is open to the first floor is nice and toasty. It's the other rooms that have the cold air coming in from the vents.
Thank you both for the input.
I didn't suggest that cold air was being drawn in downstairs. I was suggesting that something somewhere (such as the downstairs air handler or an open chimney) was expelling air out of the house envelope, creating the vacuum that's drawing air in through the non-operating ERV.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
Edited 2/1/2009 10:18 am by DanH
Ah, understood. I will add that to my investigation.
Thank you!
Dan,
That makes sense to me. Sorry I misunderstood.
I thought I'd follow up in case anyone was interested in the topic...
I disconnected the fresh air intake from the warm air plenum and found that the ductwork coming from the ERV was not cold/cool. I then opened up the ERV itself and put my arm in the duct almost to the outside vents and that as well was not cool either so I'm concluding that the ERV is not the cause of the 'not-warm' air coming from the upstairs system.
I do notice that the hot water pipe going into the air handler is warm but not hot. I also notice the pressure on the boiler is 30psi while the house is 40+psi. I don't know if either of these observations mean anything. I have the HVAC person coming today so hopefully they can diagnose the problem.
joe... it's always interesting.... tell us what the techie diagnosesMike Hussein Smith Rhode Island : Design / Build / Repair / Restore
What did you finally figure out?
So I mentioned earlier that I ruled out the ERV by taking it apart and feeling no cold air. I had a scheduled appt with the HVAC installers last Wednesday and that morning we woke up with no water so I had to postpone the appt. We will likely do late this week or next.
As an aside, we traced the water issue back to the well pump. We had an old 120 gallon galvanized tank and the pump had been short-cycling for a few days. The pump (which is 200' down the well) burned out. I'm guilty as I knew it had been short-cycling for a few days but was busy with other things. Fortunately the well guy was available and in 5 hours we had a new variable speed pump, piping, wiring, control box and little blue tank. This was a change we were going to make at some point anyway but my complacency sped up our time-table.
The variable speed pump and control box are part of a 'constant pressure' system and I have to say it's pretty great. We previously operated on a 30-45psi fluctuation but now it's constant at 65psi. Good stuff.
I will definitely post an update on the HVAC cold air issue as soon as I have one
Good to hear on the constant pressure system. I had planned to install one if our well pump dies.
Did they install metal or plastic pipe down to it? Its interesting that the previous owner of our place had the metal pipe removed and plastic installed to allow more rotational "give" in the pipe during pump start up. This supposedly reduces inertial shock at the pump and lengthens its life.
It was plastic that they pulled out and put a new 200' section in it's place. With the variable speed pumps, my understanding is that they startup slowly so they don't have that initial jerk. But what you say is certainly true of the pump we replaced.
Is there any possibility that you have flex duct (insulated to only R6 or so, jacketed) passing through unconditioned (cold) areas before reaching ceiling diffusers at conditioned rooms?This is a classic route for cold air to move, and hot air to escape, from diffuser/register areas.
Jeff
I wish it were that easy. The attic rafters were sprayed with icynene so everything is within the thermal envelope and all flex duct runs are out in the open.
Hmmm ... OK. Is the attic actually heated - or just insulated? Say on a 25 degree day what is the attic temperature? And if unheated (and if no ceiiling insulation) the heat into the 2nd floor living spaces is going to move quickly (up) into the attic.Jeff
Most HVAC guy's are unfamiliar with installing these. I just had one installed by a reputable contractor. I seen him doing things that did not make sense to me so I had him change them. I read the factory instruction manual and my suggestions were what the manual said to do. I noticed that three of the four pipes on the unit had valves and the fourth did not. I had them also install a backflow preventing valve like ones used in kitchen exhaust fan on that duct. Additionally when the unit is completely installed it needs to be balanced so it is not over pressurizing or under pressurizing the system. It should only bring in as much air as it is expelling.
Jay
First you never stated whether there was any insulation in the second floor ceiling. If there is none then you are still getting stratification with the heat from the second floor rising into the attic. Even if it is insulated in the attic there will still be cold air that will settle. I would add at least an R19 to an R38 into the ceiling. The foam insulation should only be counted on to improve the performance of the mechanical systems.
The attic is a few degrees cooler than the second floor so yes, there is too much air movement from second floor to attic and I need more insulation there. I am certain there is an issue with the HVAC though as I feel cold air coming out of the vents.
It would be instructive to measure (with a good thermometer) the actual air temp coming out of the vents. If it's pretty much dead-on room temp then it may just be the fan running with no heat. If it's actually below room temp then you're sucking air from outside.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
Good point. I'm assuming the HVAC guy will look at this first but will confirm before they show up. I mentioned earlier in the post that the hot water pipe to the air handler was warm but not hot. All my observations are just that though so hopefully the pros will diagnose appropriately.