Acceptable Heat Loss Rate for "Tight" House

[jocoman]

Guys,

Since moving into my house back in May '09. I've spent many hours in my attic, basement and other problem areas trying to better seal the envelope. I've sealed up all my exposed ductwork with mastic and been through more than my fair share of spray foam and caulk. I still need to add more insulation in my attic. It's at about R-30 levels and the new minimum for my area is R-38.

My question is...what is an acceptable rate of heat loss for a reasonable sealed house? Currently at 20 deg outdoor temps I am losing about 3 deg per hour. I realize there are probably many different factors involved in being accurate, but I'm not needing a detailed calculation or anything like that. I'm merely trying to determine if all the work I've done has made a difference. My house is noticeably more comfortable, but I'd like to know if there is any reason to keep spending time and money or if it's about as good as it's going to get.

Thanks

[ricky82g]

of course there will be some benefit from the work you have done. but i think just from sealing the envelope to cut down on the infiltration may save you a 1000 btu of heat loss on the extreme. you may save a 1000 btu at most if you insulate to r 38. your best bet buy a manual j and look at the different values when you change to certain things. you are probably right along where you should be as far as heat loos/gain.

[36183]

Guys,

Since moving into my house back in May '09. I've spent many hours in my attic, basement and other problem areas trying to better seal the envelope. I've sealed up all my exposed ductwork with mastic and been through more than my fair share of spray foam and caulk. I still need to add more insulation in my attic. It's at about R-30 levels and the new minimum for my area is R-38.

My question is...what is an acceptable rate of heat loss for a reasonable sealed house? Currently at 20 deg outdoor temps I am losing about 3 deg per hour. I realize there are probably many different factors involved in being accurate, but I'm not needing a detailed calculation or anything like that. I'm merely trying to determine if all the work I've done has made a difference. My house is noticeably more comfortable, but I'd like to know if there is any reason to keep spending time and money or if it's about as good as it's going to get.

Thanks

I actually is curious about it too. At low 30s deg outside I lost about 10 deg in 10 hours from 68F in my expanded ranch house. At high 30s deg outside I lose 3 deg in 7 hours from 60F. I have an expanded ranch house. I also think the drop was faster at the beginning.

[Shophound]

What type of windows does your house have?

Is the house single or multiple level (story)?

Are the HVAC ducts in the attic, basement, or crawl space?

In terms of heat loss of a dwelling when there's a significant temperature difference between indoors and outdoors, the main drivers are:

• Infiltration and exfiltration via stack effect (your house acting like a chimney, sucking in air from outside down low and letting it bleed out up high, such as through ceiling penetrations into a ventilated attic).
• Windows and glass doors (construction type determines rate of heat transfer, along with temperature delta across the glass).
• Integrity of insulation forming the "thermal boundary" of the house. If there are gaps of insulation missing in walls, ceilings, floor joists, etc., these areas will move more heat out of the house than others that have better insulation. Generally, these missing areas are known as "thermal bypass" areas.
• For slab foundations, edges of slab exposed to weather acts like a heat sink. For framed foundations, uninsulated band or rim joists also are a factor.

Shooting from the hip, I would expect a well insulated, well sealed house with improved low e glazing to lose heat at 20 degrees outdoors/70 degrees indoors at about one degree per hour. That's on a day with no wind, and the house is reasonably sheltered from wind (such as an established suburban neighborhood). And that's just a guesstimation.

Recently at my own house I went through a record snowfall and was without power for nearly two days. During those two days, the house temperature dropped from 70 degrees to 58, with no heat available to add to the home. The outdoor temperature hovered around 32 for most of that time. As the house cooled, the rate of heat loss slowed. I've pondered why, even after two days with no heat or power, the house was not at or near the outdoor temperature. When I walked around with my IR thermometer, shooting the floor and walls to get temperature readings I believe I got an answer, in that the slab floor, being in contact with the ground, was a bit warmer than the walls. Also, the house did have some form of heat in that the gas hot water heater continued functioning, allowing some of its waste heat to escape into the house. Nevertheless it was an interesting time...if a bit chilly!

[BaldLoonie]

You guys have too much time on your hands

[jocoman]

Shophound,

My windows I'm sure are the weakest link here. They are builder grade dual pane from 1997. I'm not even sure they are low e rated. The fact that they are probably a lower grade and that I have many of them (11 just on one north wall of my family room) I'm pretty sure is the #1 culprit for most heat loss. I have installed thermal window film on my south and west facing windows to help with the summer heat but I'm not sure what it does in the way heat retention in the cold months.

My house is a two story with high ceilings on the lower level and standard 8ft ceilings upstairs. It is about 2500 sq. ft. of finished living space with another 1200 sq. ft. of unfinished basement. I have uninsulated solid metal ducts in my basement feeding the lower level and an insulated plenum with insulated flex duct branch runs in the attic to the upstairs rooms. Each room has a return with my family room and master bed being the largest ones.

I've been through the entire attic and basement sealing penetrations, sealed and replaced the insulation on all rim joists, spray foam sealed the exterior gap between my siding and foundation, caulked around electrical boxes and added the foam gaskets to each, and replaced all door weather stripping and door sweeps.

My rate of heat loss test is far from scientific. I use a 3 deg setback at night and I've observed that it takes an hour or so for the house to reach setback temp and for the heat to come on. I'm planning on adding more blown in attic insulation to achieve levels around R-45-50 and maybe install a radiant barrier on top of it. As for my windows...It would cost a mint to replace them all and that just isn't in the cards right now unfortunately. Do you have any other advise or areas of focus that would be good bang for the buck?

Thanks for the response.

[Shophound]

What kind of window coverings do you have over your windows?

Do you have an access hatch to the attic that is in the house? Has it been made airtight? The pulldown stair type access hatches are horrible leakers.

You said your basement is unfinished...does this also mean it is not heated or cooled? Is the door leading down to the basement from the house weatherstripped?

May I suggest you purchase an inexpensive temperature and humidity meter? You can get decent digital models for not much cost. Set it up in the room where you feel the least bit comfortable. Make a note of both temperature and humidity levels. You can also rerun your rate of heat loss test using the meter vs. the thermostat.

If you get the meter and find your interior humidity levels running low, you know there's more leaks around that is driving humidity levels down. If you find your humidity levels fairly stable, even as weather conditions fluctuate outside, your sealing efforts are showing some effect. If you see indoor humidity levels rise when there's a lot of moisture generating activity going on, such as cooking, dish washing, and showering/bathing, that's another indication your house does not ventilate naturally at the same rate it used to. If you find your indoor humidity levels are low and stay low regardless of indoor activity, that can indicate further leakage.

The main caution regarding tightening up a house is toward how tight can it get before one has created an unhealthy indoor environment. That is what a blower door test done by a well trained person can do...help you determine if your house is adequately ventilated, and also find where leaks are in the house. You may not have crossed that line yet with your tightening efforts, but if you really want to know where you stand, a blower door test is something you may wish to consider.

[amd]

The main caution regarding tightening up a house is toward how tight can it get before one has created an unhealthy indoor environment. That is what a blower door test done by a well trained person can do...help you determine if your house is adequately ventilated, and also find where leaks are in the house. You may not have crossed that line yet with your tightening efforts, but if you really want to know where you stand, a blower door test is something you may wish to consider.

I don't think it's possible to make a house too tight, provided that...

1. Natural draft combustion equipment isn't used

2. Proper mechanical ventilation is provided (could be as simple as running exhaust fans

[jocoman]

Shophound,

All of my North facing windows have no window coverings. My wife and I like the open view they provide. All of my South and West standard windows have thermal film installed as well as wood blinds. I also have several accent windows (large half rounds and rectangular fixed glass) that I've installed the thermal film on but no coverings.

I have two weather stripped and latched attic scuttle hole entries. One in my master closet providing access to the majority of attic space and one in the garage providing access to only the space above it.

My basement does get supply heat since we spend some time down there exercising and playing games and yes the basement entry door is weather stripped.

I will have to look into the temp and humidity meter. I've never thought to look for them. It does make sense however that the level of humidity is a direct reflection of infiltration.

I have considered the blower door test primarily based on reading this forum. I just haven't pulled the trigger because I had to fix some of the more obvious problems first. Now that I'm to the point that I've done most things I can think of, it may be time to get that done in order to reveal the unknowns.

Thank you for your time and assistance.

[Shophound]

I don't think it's possible to make a house too tight, provided that...

1. Natural draft combustion equipment isn't used

2. Proper mechanical ventilation is provided (could be as simple as running exhaust fans

That was my point in my reply, although perhaps I did not articulate the aspect of mechanical ventilation succintly. If the ASHRAE minimum ventilation requirement is to be the benchmark to determine if a dwelling is adequately ventilated or not, this is what a blower door test can achieve. If the house is tight enough that it can't ventilate itself naturally enough to achieve a minimally acceptable rate of fresh air turnover, mechanical ventilation must then supplement the difference.

On principle I agree that it is not easy to get conventionally built residential construction extremely airtight, but our comments and replies go out to a wide audience. Therefore I deemed the caveat necessary to state. I have no idea exactly what the OP has done to tighten up his house, other than what he has disclosed, so I'm not in a position to say whether he's too airtight or not. Only on-site data can determine if that is true or not.

[Carnak]

I did a lot of R2000 homes back in the day

Indoor outdoor differentials be 95 to 100F

Take the total sqaure footage including the basement and it would be about 13 btu/hr per square foot, some even lower

[jerryd_2008]

...

My question is...what is an acceptable rate of heat loss for a reasonable sealed house? Currently at 20 deg outdoor temps I am losing about 3 deg per hour. ...

...

My house is a two story with high ceilings on the lower level and standard 8ft ceilings upstairs. It is about 2500 sq. ft. of finished living space with another 1200 sq. ft. of unfinished basement. ...

Don't know if this helps, but my house is at least 1,000 sqft of living space bigger with no basement but the lower level surrounded on 2 sides by garage. When we lost electricity and heat during January 2009 for 3 1/2 days after an ice storm, the house never dropped below 50 F AT THE TSTAT - was a bit lower at the extremities. The only heat was from a wood fireplace in the lower level that you could not feel more than 10 feet away and the daily heat gain from south facing back of the house with shades up. We did cook with NG and the NG HWH in the garage provided some hot water. That's it!

We did put in a new NG fireplace insert after that experience though. Even without the electric fan, we figure that the natural convection from the insert would add enough heat in the lower level.

A more recent example was when I woke up and the house was 64 F with no heat, down from 70 at midnight. I don't know how long it was out and the furnace blower could have been running while blowing cold air.

The point is that it depends on the house but then again IMO 3 degrees per hour seems like a fairly high loss for a "tight" house.

[Shophound]

The point is that it depends on the house but then again IMO 3 degrees per hour seems like a fairly high loss for a "tight" house.

In the OP's case, his house could be totally air tight, but with a lot of marginal windows he will still experience heat loss at a fair clip when there's a considerable temperature difference between indoors and outdoors. R value is the key...if you take a solid R23 wall and poke it full of windows, the average weighted R value of that wall assembly could be pitifully lower, say R11 or less.

[jocoman]

[QUOTE=his house could be totally air tight, but with a lot of marginal windows he will still experience heat loss at a fair clip[/QUOTE]

Yes. That's really what I'm trying to quantify. As stated in my previous post I do in fact have many marginal windows. I should clarify something from the original title. I'm not claiming MY house to be tight. I'm trying to determine what is acceptable for a home that is for comparison's sake. My goal is to get my house as thermally sound as possible given that I need upgraded windows. Without knowing what is considered "good" in terms of heat loss I'm not sure how to determine the effectiveness of my efforts. Going forward, if I know I've done everything I can and my heat loss is still not acceptable without a major investment in new windows then I have to weigh the cost vs reward in terms of comfort and efficiency.

Do any of you have a brand of replacement window that you would recommend? From my past experience it's not unlike HVAC equipment in that a great window installed incorrectly is a bad window.

Thanks

[jerryd_2008]

... with a lot of marginal windows he will still experience heat loss at a fair clip when there's a considerable temperature difference between indoors and outdoors. R value is the key...if you take a solid R23 wall and poke it full of windows, the average weighted R value of that wall assembly could be pitifully lower, say R11 or less.

We have a pretty full southern wall of windows and patio doors (swinging, not sliding) on 2 floors. I was concerned when we moved in about the vinyl, double hung windows. They appear to be pretty good though. Biggest issue is the sun load in cooling season. Need to pull the shades.

I was also pleasantly surprised to find that the southern wall is 6" (Maybe structural reason for 2 stories high) and that there is a layer of foam board between the studs and the brick. Never having lived in a largely brick house, I was quite surprised how warm brick can get in the summer sun. That extra foam board is very useful, me thinks.

[Carnak]

In the OP's case, his house could be totally air tight, but with a lot of marginal windows he will still experience heat loss at a fair clip when there's a considerable temperature difference between indoors and outdoors. R value is the key...if you take a solid R23 wall and poke it full of windows, the average weighted R value of that wall assembly could be pitifully lower, say R11 or less.

2400 sq ft of R11

60x40x 9 feet high

100F differential

(60+40+60+40)x9x100/11=16,363 BTU per hour

0.7 ACH --> 2400x9x.7/60x1.08x100=27216 Btu/hr

R20 roof

60x40x100/20 = 12000 Btu/hr

(16363 + 27216 +12000)/2400 =23 Btu/hr/sq foot

maybe add something for the floor and be about the same as a house built to the 1970s Ontario Building Code,