Value of insulation in an old brick construction??

jp_2

it would be best to insulate the outside, this would give you the chance to seal up leaks where they start, not where they stop.

but insulating interior walls to r19 would make a big difference.

find a heatloss calculator and play with some numbers, sounds like brad gave you some good stuff to go by.

I see no real benefit from heating the entire mass of the house exterior brick that is, only if you were trying passive solar.

Eric L._2

Value of insulation in an old brick construction??

I have a home in the NYC area which was built in 1926.I have been reading here that it makes more sense to insulate the outside of the house in order to take advantage of thermal mass effect. My house is brick and I can't see doing that to the whole exterior. My question then is if I redo my outside facing interior walls to R-19 using Polyisocyanurate board will there still be benefits to fuel savings / comfort level and if so will it be worth the trouble and expense? Currently the walls are composed of a ferring strip , wood lath , and plaster which alltogether including the airspace is about 1.5 inches from the brick exterior. Thanks in advance .

Eric L.

Jim Pompetti

try

www.coloradoenergy.org

Eric L._2

Value of insulation in an old brick construction??

Great site but I can't seem to find an answer to my original question of outside versus inside insulation.

Eric

Brad White_9

Details are Critical, Eric

Especially in how the rain is kept out. The detailing and aesthetic considerations may outweigh your altruism. If you insulate from the inside however, you will not get the coverage you seek. If you have to re-point the brick and major maintenence is in the cards, and the historic/aesthetic aspects are not critical to you, then by all means insulate from the outside. Just keep water out between the new and old systems. Books abound on this.

As a strictly thermal approach, if your walls have 8 inches of common (not face) brick, the u value will be about 0.257 (u=Btu's per hour per square foot per degree F. difference)

R=3.9 more or less.

If 12 inches of brick this drops to about 0.213. (Lower is better.)

R=4.7 more or less.

In order to meet R-19 and the aged polyiso is taken at 6.0 per inch R value, you obviously need to add 2 to 2.5 inches at least, plus weather protection.

Whether you add the insulation on the inside or outside does not change the overall u value but the ability to retain heat over time is affected. A minor paradox of heat transfer. Your warm-up times and ability to re-radiate into the space (forestalling the need to add heat) is the benefit to external insulation. When you insulate from the interior, you probably never really warm up that brick except in summer and by then, who cares??


Quick Heating Cost Comparison:

Stipulate 80% efficiency, 10 degrees outside and 70 degrees inside, 5000 degree-days and gas at $1.50 per therm for this.

1,000 SF of your existing wall (8 inch brick for now):
15,420 BTU's per hour loss.
Annual Cost to Heat: 231.3 therms x $1.50 = $347

1,000 SF of the same wall improved to R19:
3,158 BTU's per hour loss.
Annual Cost to Heat: 79 therms x $1.50 = $119 rounded up.

For every 1000 SF you insulate you can save about $228 per year at 80% efficiency with gas at $1.50 per therm.

If it costs you $2.00 per SF ($2000 for our wall sample) to insulate and finish (who knows, just a wild guess), the simple payback would be almost 9 years. With financing costs maybe 12 years. If fuel costs escalate this will be shorter.

Hope this helps.

Eric L._2

Value of insulation in an old brick construction??

I truly understand what you are saying about payback but the sad truth is that this house has probably gone through almost 1550 gallons of fuel oil since October of 2005. On top of that my living room is never really confortable and the outside facing walls are always cold to the touch everywhere in the house when the temperature drops. I am going to caulk the windows and seal everything I can this spring but I just can't see that making a huge difference next year in my costs and comfort level.

Brad White_35

Comfort has value but no price

Gosh I should start writing pithy Hallmark Cards....

How big is the house, Eric? And how leaky is it (infiltration?).

No doubt the radiant effect of cold masonry penetrates. I was in the garage of a high rise early this afternoon. Temperature about 30-35. The cold got to my bones. Sunlight was welcome.

Seriously, if you are in the house for the long haul and you are handy, by all means insulate it and from the outside if that works for you. Contracted-out the payback will be much longer. Sweat equity where you can, use the pros when you have more sense than skill.

Good Luck!

Brad

Eric L._2

Comfort has value but no price

The house is a two family about 2900 square feet total living space with almost 600 square feet of EDR in radiators. I just had r-38 blown in (cellulose) to the roof crawlspace. I am more than willing to do as much of the work as possible but I just don't want to do anything that will not pay me back in some sort of comfort and efficiency. Thank you for all your advice.

Eric

Brad White_35

You know, Eric

Your heat loss (relative to your 600 EDR radiators at 150 BTUH per SF EDR) is 90,000 if hot water. At least that is what your radiators can emit. That is only 31 BTUH per square foot of floor area. Quite respectable for an older house without insulated walls.

If it is steam (I do not think you said one way or the other), that rises to 144,000 BTUH or 49.7 BTUH/SF which seems more reasonable. (Had to go through that to get there you see.)

If the 144 MBH really is your heat loss (SWAG here that the radiation matches the load), and your system is 70% efficient, you should be using about 1555 gallons per year of oil. That you are using 1550 gallons indicates a system well sized at least. Point of reference. But now you can get that down a but.

With a conscientious program and good detailing you will increase your comfort significantly and reduce cost. If oil goes to $3.00 a gallon your pressures increase but the decision is easier.

Good luck!

Brad

Eric L._2

Value of insulation in an old brick construction??

If you don't mind me asking,what program or book did you use to do thes calculations? Thanks

Eric

Brad White_9

No program

just standard formulas and years of experience

I can tell you but then I'd have to...

Nah. I can share... ASHRAE Handbook of Fundamentals has abundant information on most anything you would care to know about HVAC. Their chapters on heat conductance of materials is legion and there are other sources.

It all gets down to (AREA in SF x u-Factor x Delta-T) for every surface of a given material composition (wall, glass, roof...). Then infiltration based on an assumed air change rate.

chuck_6

Insulation in old brick house

Eric:

We live just north of NYC in an old brick house as well with plaster walls. It was drafty when we moved in (no longer), but a few things to consider:

1) Have the interior walls (the ones exposed to the outside) blown in with cellulose insulation. Call NY Energy Conservation at 1-800-461-4669.
2) You probably have single-pane windows. Go with double-pane windows. It helps.
3) Have your doors properly weather-stripped. Call John Myron at (914) 497-5074.
4) Make sure all of the radiator vents have proper vents, and as important make sure your main vents are properly vented. Go with Gorton vents. Speak to Ken Kunz at Gorton. His number is (908) 276-1323.

Chuck

Eric L._2

Value of insulation in an old brick construction??

I wish it was as simple as that the construction of the walls consists of interior side of brick frame , 1x2 ferring strips nailed to the brick , wood lath nailed to that , and finally plaster on the the lath. There is maybe 1 inch of airspace behind the wall. Thanks for for the suggestions just the same.

Eric

Eric L._2

Value of insulation in an old brick construction??

Thanks everyone for your time and wisdom.

Eric L.