house AC / Heating question

[rieferman]

I know there's a section for this type of stuff, but so many more hang out in Free Parking, so please forgive my transgression.

Our little old farm house has a walk up attic that we use as a guest room and office. The finished ceiling up there is affixed to the underside of the roof rafters, with minimal insulation. This was finished by previous owner, and I plan to remedy the insulation issue at a future time.

To get up to the attic, you walk up a center stair. Office is on the left, guest room on the right. Open doorways lead you into each of the rooms. No doors.

Our house has two heating/cooling systems. One system for the 1st floor. And a heat pump is located in the attic office to heat/cool the 2nd floor and attic.

The air return for the 2nd floor and attic is a single, common air return that is located at the top of the attic steps, but before you enter either of the rooms that are up there. Air is pulled from all the rooms, up the stairs and into that common return.

Since the roof is poorly insulated, I battle heat loss through the attic in the winter, and heat gain during the summer. The trunks to the attic rooms are not large enough to compensate for those issues.

Again, the real solution is to pull down the ceiling and insulate. Or some other crafty solution. Not in the budget for probably 3+ years. The rooms are only occasionally used.

SO.... My thought is this....

If I add doors to each of the attic rooms, and keep them shut when the rooms are not in use, I can effectively "block" about 75 percent of my roof problem from affecting the temp controlled portion of my place. Only the roof area above the attic stairs (which must be left open to allow the air return to draw) would be affecting my heating/cooling performance. Plus, the doors would enable guests a bit more privacy when they stay.

To supplement this solution, I have a small window AC unit that I was planning to put in the window of the guest room as it is difficult to make comfortable on hot days.

QUESTIONS:
- Do you agree that the doors solution will significantly help buffer the poorly insulated roof situation away from the rest of our conditioned space?

- When the doors are shut and the rooms are not in use, should I shut the dampers to the vents in those rooms? I.e. leave those rooms entirely unconditioned when doors are shut and rooms are not in use?

- Any issues that you can foresee with the supplemental window AC unit for spot usage when guests stay over?

 

[yeldogt]

Being able to close dampers will depend on the size of the remaining trunk lines -- the HVAC unit needs enough flow over the coil to work properly.

Closing off sections of the upper level and allowing those areas to become somewhat unconditioned may impact the comfort level of the rooms under them -- this will depend on the insulation protecting those areas and air leakage to them.

I'm starting a project next week to replace both of my current old HVAC systems and insulate the structure to fix a similar problem with an extended cape cod.

I'm taking down a couple of ceilings and spray foaming the roof decks -- sealing up all the remaining ceilings -- removing my second system from the attic and going with mini split cassettes. It's expensive - but the only way to make my life here enjoyable for however longer I own the place.

I would try covering the doors with plastic or cardboard -- to test what happens. Adding additional AC obviously will help -- it all boils down to what results you want.

 

[Jagmandave]

The little window unit will help considerably......I don't see a downside for it except the extra electrical cost, and that's worth it for the few times you'll use it if it's just a supplemental for when guests are using the rooms.

I agree with taping off the doorways with plastic and seeing what the results are.....

 

[rieferman]

One more question to add to the mix after reading yeldogt's post above. I agree that shutting those dampers could have a negative impact on the system - my HVAC guy (who did not do the original install, but who I trust explicitly) is coming over this week to advise me on that.

Supposing he agrees that those dampers need to stay open...

If I leave the dampers open in the rooms while the doors are shut, those rooms will be conditioned to some degree still, but I'll still be buffering the rest of the house from the poorly insulated roof situation to a large degree. Therefore beneficial, from an HVAC efficiency perspective, to do the project still, even though I'd be sending conditioned air into those two rarely used rooms. What do you think?

 

[Milton Shaw]

Keeping the doors closed will keep the cool air in the rooms instead of it going down the steps and cooling the lower floor. Rooms upstairs will be a lot more comfortable with doors closed and you might be shocked at how much cooler they stay. Almost all two story houses have problems with upstairs air going downstairs to cool off the lower floors. A lot of houses the first floor units hardly run at all because the upstairs units air is keeping the lower floor cool.

 

[reader2580]

shocked at how much cooler they stay. Almost all two story houses have problems with upstairs air going downstairs to cool off the lower floors. A lot of houses the first floor units hardly run at all because the upstairs units air is keeping the lower floor cool.

My previous house was a two story built in 2001 with zoned heating/cooling. If I didn't air condition the 1st floor at night the heat from 1st floor would flow up the stairs and hit the thermostat upstairs. This would cause the air conditioner to run making it very cold upstairs. There really should have been a door at the top or bottom of the stairs to help with this. I had to run the air conditioning at the same temperature for both floors at night to not have issues. Luckily, my electric bill never went above about $100 during the summer.

 

[volleyball]

I'd rip down the ceiling and get proper insulation up there first. Then sheetrock when time and money become available. If you patch it, you will put off what you need to do and will only end up spending more money.

 

[G McKay]

You can always cut holes in the upper corners of the ceiling and blow insulation into the ceiling between the ceiling and the roof. I think that would be my solution.

 

[rieferman]

I'd rip down the ceiling and get proper insulation up there first. Then sheetrock when time and money become available. If you patch it, you will put off what you need to do and will only end up spending more money.

Regardless of whether I insulate the ceiling, I plan on adding doors. So I don't see any harm in doing the step now.

 

[rieferman]

You can always cut holes in the upper corners of the ceiling and blow insulation into the ceiling between the ceiling and the roof. I think that would be my solution.

Our roof has soffit in ridge vents, and there are not baffles installed at this time. So blow and would create some issues for air circulation.