Unheated basement in heat loss calc?

mjj_2

Thanks for your input Mark. Initially I was going to keep the basement out of the building envelope, except it is completely uninsulated and has a stone foundation, therefore contributes to the heat loss. The house has knob & tube wiring, so insulating the basement is not an option at the moment.

The area of house is ~2000 sq. ft., with a basement area of 540 sq ft. My heat loss excluding the basement is 95,000 which jumps to 108,000 BTUH when the basement is included. A difference which surprised me, but I guess that's to be expected with a drafty basement. Our mains are insulated with asbestos(it's an old house).

mjj_2

unheated basement in heat loss calc?

Not sure if I should include the unheated basement in my heat loss. Heating contractor says "no" (we aren't planning to install a basement radiator). Heat loss software developer says "yes" because the basement is heated through infiltration, and old boiler is radiating heat (although the new boiler will be better insulated). Including the basement makes a significant difference in my total heat loss. I'd appreciate your tips on this.

[Deleted User]

Insulate...

the joist bays and see what it does to your equations. Also, you don't use the regular delta T for the basement. 15 degree delta T would be a LOT.

A/R*Delta T = heat loss. If you insulate to R19, the loss per square foot would be 1 divided by 19 and that sum times 15 = .78 btuH. that works out to 789 btuH per thousand square foot building space. So on a typical average 2,000 square foot floor plan, that equates to 1,578 btuH. 1,578 divided by 500 (the btu's a human puts out at rest), you would need 3.15 PEOPLE to counter that heat loss. That, or 502 watts of electrical appliances, including lights, computers etc, to be running inside the heated envelope...

How big an impact did you think it had?

How big a space you conditioning?

Personally, I'd insulate it, and forget it. Don't add it to the heat loss.

You've got LOT of other things working in your favor.

You'd be wise to isolate the mechanical room with its own shell, give the appliance sealed combustion whenever possible, and don't forget to protect the main water lines etc...

I din't use to heat my basement either, other than the duct losses and it was just fine.

ME

Mike T., Swampeast MO

If you have hot, humid summers, be very wary of insulating the joist bays in an old house--particularly with fiberglass. You'll get condensation in the insulation and rot your floor joists (even good old lumber) with amazing speed.

My "take" on old house basements is that the I=B=R rating will easily account for any losses in the basement mains. The ground floor heat loss should include loss through the floor at a reasonable basement temp (say 50°).

Scooter Libby

> Initially I was

> going to keep the basement out of the building

> envelope, except it is completely uninsulated and

> has a stone foundation, therefore contributes to

> the heat loss.

If the basement is getting heat in winter (maybe not 70F, but much closer to 70F than to 0F when it is 0F outside, say it is at 60F) then the basement IS inside the building envelope. You can't leave it out of the envelope when doing your calculaions. It is only outside the envelope if you insulate between the basement and the rest of the building, as suggested above, and then the basement will get freezing cold in winter. (This may cause harm to your water pipes.)

The basement is a very large contibutor to heat loss in an old house. Most of it is because the foundation is not a good insulator and leaks heat like a sieve. If you can't insulate the foundation, you have to live with it.

mjj_2

Thanks for all of your advice.

Even the conservation audit technician, who did his own heatloss on our house, admitted that insulating basements is risky because of the resulting accumulation of moisture. I believe his heatloss included the basement, and mine will too. Thanks for the suggestions, looks like we'll be choosing a slightly larger boiler after all.

Steve_35

The answer is...it depends.

If the software our heating contractor is using is WrightSoft's Right-J and Right-Draw the answer is no. The software accounts for the heat loss through the floor into the basement.

If you're using ACCA Manual J 7th edition the answer is no. The HTM for floors over unheated basements takes the loss through the floor into account.

I can't address any other methods because these are the only two I've used.

What software are you using? Is it ACCA approved?

Mike T., Swampeast MO

So How do You Compute Heat Loss for an \"Unheated\" Basement?

Even if the foundation is completely uninsulated, you can't assume that the walls are anywhere near the outdoor ambient temperature. Much or most of those walls is in contact with the earth and once you get down a couple feet, it's considerably above freezing in most US climates. You also have the floor that will act as a radiant source of heat as the air temp tries to drop below the temp of the floor.

You certainly can't base your loss on "room temperature" air.

Then with any heating system you have heat sources (losses) to the basement.

Mike T., Swampeast MO

Before you increase the size of the boiler because of your basement, look at the I=B=R rating. If that rating is near or even slighly below your calculated loss, there is very little chance of ANY problem. Just remember: nearly every step of the heat loss calculation process is overstated as to loss and there is ZERO consideration for heat gains via occupancy.

Steve_35

If you use ACCA Manual J

The loss to the unheated basement is taken into account when you use the HTM for the first level (area over the basement) floor.

Additionally there is a piping and pickup loss factored into boiler ratings. A boiler has 3 separate ratings. Gross, net or DOE and IBR. The IBR rating allows for a 13% piping and pickup loss.

Steve_35

Mostly correct

It's assumed there's sufficient activity in most homes to maintain the home at 70 when the outside temp is 65.

Mike T., Swampeast MO

Then why do Manual-J based heat loss programs still show a loss at 65 degrees out and 70 in? Infiltration?

[Deleted User]

Equalibrium...

Theoretically speaking, the point of neutrality for heat losses has always been stated as being 65 degrees F. In reality, the neutral point is MUCH lower than 65 degrees F. In some cases, mine for example, the point of neutrality is around 50 degrees F. And I've not done anything special to get it there. That's just where it is. It's influenced by internal gains and solar gains and thermal flywheel mass and so on and so forth.

If we get fixated on things that we've been taught for so long, we loose sight of what happens in real time...

ME

Mike T., Swampeast MO

My "point of neutrality" is about 55° and that's with very little occupancy gain.

Steve_35

We know that people being in a room is a heat gain

I know ACCA Manual J 8th requires so many CFM per person. I think it's 15 CFM but don't know that for sure. I use WrightSoft's program and as you add people the infiltration goes up. This is to meet ACCA's requirement. Does the infiltration really go up? Who knows?

I mean there are more door openings per hour but I think they're looking at forced ventilation per ACCA's requirements.

In addition there is some envelope loss shown but when you look to heating degree days it's based on 65 starting point, not 70.

Tim_24

An unheated basement

serves as a heat sink for the spaces above, especially, the foundation walls. A structure, on slab with 4 foot foundation walls will experience the same losses as one over an unheated basemwent. The total heat loss associted with perimeter losses will be signifcantly less that if the entire basement space were to be heated to a comfortable temperature, but they are not negligible. You should account for the heat losses. Obviously, construction/insultion details are required to calculate this loss accurately.

mjj_2

the heatloss program I'm using is in accordance with

ACCA Manual J 7th Edition (HVAC-Calc 4.0). I'm not sure if it's skewed to exaggerate heat losses, since it takes into account numerous heat gains,(each occupant contributes a heat gain of 530 BTU/h) and can be use to size air conditioning as well as heating equipment. In calculating, I included both losses from the first floor to the unheated basement as well as basement floor and foundation wall losses. From your comments and advice this seems accurate. Thanks for the tip to check the I=B=R rating of the new boiler!

Steve_35

AFAIK, WrightSoft and Elite make the only ACCA approved

software.

That said, I KNOW ACCA Manal J does NOT require you to add in for areas that are unconditioned. That means if you have a basement, enclosed entry or any other part of the building that's unconditioned you do NOT need to consider that area in determining your heat loss. You simply use the apprpriate HTM for the surfaces where heat transmission will ocurr.

Let's consider an enclosed porch on the front of your home. NO conditioning whatsoever. Would you add that to the heat loss calculations? Heat definitely moves from the warm side of the wall into the cold porch. Obviously, you wouldn't consider including the porch. Why then would you consider adding an unconditioned basement? It's just another cold surface. Manual J gives you what you need through the use of the appropriate HTM. It accounts for the basement being colder, just not as cold as the outdoors. Manual J 8th takes more factors into consideration like are the basement wall insulated? Is it a tight or loose basement/crawl?

So my basic question is why would anyone include an unconditioned basement in heat loss calcs if they're using Manual J properly? And if you are going to include an uncoonditioned basement would you also include an unconditioned, enclosed porch?

Constantin

Note...

... if you look at your heat loss reports, the heat gain from occupants, insolation, equipment, etc. are NOT used, IIRC, for the heat loss calculation.

In other words, the program assumes a full, sunny house with appliances running full steam in the summer and an empty house on a windswept night in the winter.

So, if you want to start adding up little heat sources, you'll have to add them back into the heat loss calculation.

Mike T., Swampeast MO

Exactly Contstantin! The gains from people, lighting, appliances, etc. are only used for assessing the cooling load.