Temperature Variations in Pretty Good House
Hello I am hoping someone can help us figure out what is going on in our new house. We were shooting for a pretty good house with regards to design and insulation. We spent a lot of time working on an efficient plan and making sure it was air sealed and insulated well. It is a two story house with R7.5 zip R and bibs 2×6 walls. We had a manual J S D and T done and used webbed trusses to keep the ducts out of the attic. The house has three HVAC zones one each for the basement main level and upstairs. We have a Panasonic ERV. The problem we are having is all of our bedrooms are on the second floor and the thermostat is in our master bedroom. The master bedroom runs 5-8 degrees warmer than the kids rooms. I cannot figure out why this is. Our HVAC system rarely runs especially this time of year. Our furnace has not run all day and it’s 65 in the kids rooms and 72 in the master. Our bedroom has by far the most Action with two people sleeping in there, two dogs, kids coming and going, showers etc. I am wondering if body heat alone is enough to heat up our room. This last weekend it was in the 60s and we had the windows closed and the thermostat called for
cooling upstairs. I have tried bumping up the ventilation rate as we have the blower set to run continuous since our erv is tied into the ducts. I am going to set up our bath exhaust fan to run a little longer than it has to make sure all the heat from baths and showers are exhausted. Does anyone have an ideas on what we can try to do I order to even out the temps or what is causing such extreme temp differences even when nothing is running? It is disappointing that we spent so much time and money trying to do things right and we can’t seem to get things dialed in
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Seeing a floor plan of the house would probably help to uncover and rule out possibilities.
In my house, my kid's room has east and south facing exterior walls, and the master bedroom has only a north facing exterior wall. Until I zoned my second story HVAC to have independent control over those two rooms, it was not uncommon to see a 5 degree temperature differential between the kid's room and the master. I assume the difference was largely due to the massive solar gain difference. My kid's room basically got sun from sun up until sun down. The master got almost no sun.
Unfortunately, I find HVAC contractors to be the hardest subs to do things right in home building. There are so many things possible here. Just because all manuals were performed, doesn’t mean there were done right, and usually they are horribly wrong. Zoning is usually unbalanced. The fact that your kid’s bedroom are in the mid-60s and yours is 72, tells me that the ducts, fittings, elbows, etc. were not sized, selected or installed correctly. The equipment may not have been selected properly. There are differences on performance with metal vs. flex ducts as well.
Bottom line, without looking at all information (manuals), looking at all product installations, etc., I think it would be impossible for anyone to be accurately describe a prescription. My point here is that your situation is complex, with too many variables, and you need to find an experienced building analyst (HERS Rater, BPI) to come to your house and look at your situation.
I’m also assuming the building envelope tightness, glazing, quality of insulation installs, etc. were done correctly. Did you guys do a door blower test? What’s the ACH50?
Thanks for the input I will try to get a floor plan posted later. In full disclosure I am the owner of an hvac company so we were of course responsible for the install. All the manuals were done by a third party that does them for a living. We tested and balanced our hvac system and it is performing as designed. I may be biased but the hvac install as good as anything out there. We have yet to compete the blower door test and I did not have a HERS testing done as it wasn’t necesaary and was relatively expensive. I would be the first to admit if it were and issue with the hvac but the problem gets better the more the system runs. We did fine all summer but the shoulder season is where we are having trouble. The less the system runs the greater the temp difference. The more it runs the better it gets. I understand it’s easy to point the finger at the hvac guy and believe me a lot of the time we deserve it but it seems strange the problem gets worse the less the hvac runs
> ... even out the temps
> we have the blower set to run continuous since our erv is tied into the ducts
Compare each room pressure to outdoors. Could be that the blower (or wind) are creating infiltration in the other bedrooms and only ex-filtration in the master. Also look at electrical loads (eg, I have a TV that heats up the room).
Zone the system if the load difference is caused by things you can't reasonably change.
Note that "balanced" is a myth of the HVAC world - various things cause it to change.
Thanks for the suggestion I will get my monometer set up this weekend. You are correct about balancing being misused- when I say “balanced” I mean that we have adjusted each supply’s air flow to meet the airflow specified by the Manual J and D
People and dogs and kids (people of sorts) definitely give off heat. People tend to use power as well (TVs, computers, tablets, phones, lights, chargers, etc), so it's not just people, it's the people and their things giving off heat. If the doors are closed, a lot of that heat will stay in place during the shoulder seasons when the forced air isn't moving a lot of air around.
I'll be interested to see what you find with your manometer.
One thing to try: run the fan blower continuously on low (no cooling or heating, just the fan). It may help distribute the temperature more evenly across rooms. This isn’t a structural fix, but for now it may help solve the comfort problem.
This is a common problem with well insulated houses. 60F is probably near the balance point of a house with R26 walls, at that point room temperatures are very sensitive to amount of heat generated by the occupants. You can get a fair bit of difference between rooms just from the fact that some of the bedrooms can have anywhere from 1 to 3 outside walls. If your master is in the middle of the house and the kids room in a corner, it will definitely be hotter.
Unfortunately, without active cooling, HVAC fan won't move enough heat at the typical flow rate set up for cooling/heating a room. Your best bet is to turn down the register in the kids room and run cooling in the evenings upstairs to keep your bedroom in check.
There is probably no easy fix for this without further zoning. You can try adding some dampers/thermostat instead of balancing damper to control the ratio of air flow delivered to each room. You don't want this damper to completely shut of the flow, just reduce it a bit to divert flow to rooms that need more cooling.
As long as the extra damper does not effect the overall flow through your air handler too much, you wouldn't need to integrate it with the zoning controls. The hallway thermostat would control the upstairs temperature, but this extra thermostat/damper for the kids room can reduce the cooling flow a bit there to keep it from freezing.
Thank you all for the suggestions and tips. I had an energy audit done on the house and it turns out the two dormers above the kids rooms received about 1/3 the blown in that the rest of the attic received. When the roof was sheathed it was done before the dormers were put on and access holes where cut later The perimeter of the dormers did not get insulated as well as was called for. Additional blown in going in next week but I am hopeful that will help the issue
Thanks for the update
Please do lot us know how it works out.
Walta
Each person and large dog gives off roughly 200 Btu/hr. With good levels of insulation and air-sealing, that adds up. There may well be other issues as noted above. I always include a short length of electric baseboard in bedrooms and bathrooms that don't have a mini-split head, so occupants can fine-tune their temperature in winter. The baseboard doesn't have to run much--in a case like yours, bringing the temperature up 7° won't take much energy.
>"Each person and large dog gives off roughly 200 Btu/hr"
Depends on the dog- some put out considerably more than that, even when sleeping. A short-haired Great Dane or English Mastiff may even be putting out north of 350 BTU/hr while sleeping, (but I'd like to see hard data on dogs as space heaters, if anyone can point be to it.)
IIRC Manual-J assumes 230 BTU/hr per sleeping human for cooling loads. It may be a bit higher than that during the heating season due to a lower presumptive room temperature.