frost/condensation-free jobsite heat?

KW_2

Guys,


I didn't mean to sound testy in my reply - I just have a feeling I'm missing something basic....

KW_2

frost/condensation-free jobsite heat?

OK, you Wallies have helped me corner the plan for hydronic heat for our project (I'll post a summary at some point). The plan included a forced air unit - but thanks to your encouragement, it appears like we'll be fully hydronic with a modcon Munchkin as a heat source (properly sized, thanks again to everyone!)


OK, next question. Need to heat an uninsulated home (new construction) in order to insulate with spray foam. Spray foam needs a 40-45 deg substrate temp - but DRY. Ambient air temps are in the teens at night - up to 25-30 during mid afternoon. So any ideas how one goes about heating the substrate (roof and wall sheathing) to that temp??? It would seem that as soon as you start heating the air in the house, you are going to instantly develop condensation on all of the cold surfaces (basically the entire inside of the house!) If you continue to heat it, will you dry up the condensation? Or will it simply continue to be generated?


I understand that I need to have a combustion separate from the space - either a sealed combustion furnace or ???? in order to prevent moisture from the fuel (LP or kerosene from adding to the moisture problem. Electric sources would be good too. Any type of electric radiant heat that could be 'pointed' at an area (say 8'x8'?) of sheathing for a few minutes to warm the substrate?


Like to hear some creative ideas for this. Project at a standstill if I can't make this happen. I'll post more info if needed.

Sorry for the l-o-n-g post....

Brad White_22

So long as the

combustion means is indirect fired and vented away from the space, as you note you will not add that kind of moisture. If you can go hydronic I would use propeller unit heaters either vertical or horizontal Modine or other types.

If electric is your choice, radiant quartz heaters such as by Markel or Detroit Radiant or others would be great. We use them in air handling units to keep dry snow from soaking filters. Heats surfaces not the space itself and you can aim them. Do not use the direct-fired gas radiant heaters or you are in the same boat as if you were using a propane salamander.

brucewo1b

They do make large propane and oil fired furances that you duct in and out of a building and the furnace is outside someone near you rents them out
http://www.etopp.com/page.php/temporaryheatersindirect.htm

Brad White_22

Yes

We are using them on a new 35,000 SF music building. Makes a nice job. Just a little tough to direct the air at surfaces. But point well made, they can heat without adding all of that humidity.

KW_2

heat sources

Thanks for the info guys.

The electric radiant heaters mentioned might be perfect - I noticed some radiant heaters designed for outdoor spaces like patios. It would seem like a pair of these could be moved along in front of the foam installer - seems they would raise the substrate temps in a matter of minutes. Also, boiler is not installed yet - and won't be until this work is done so a hydronic fan coil is not an option.


For heat sources...in one space I have a Reznor LP hanging furnace - power vent unit vented to the exterior (this is a UDAP model, 83% model, not the UDAS (sealed combustion) model)


In the other space a have a forced air furnace (PVC vented to the exterior) in the basement as temp heat. No duct work but stairwells are completely open between floors.


From what I'm reading of your posts, this should warm the space (substrate??) without creating condensation, right? This seems odd as I would have thought that any warm air is relatively moist compared to the cold exterior air so I would expect condensation (like you find in a wall cavity where interior air is leaking through the insulation and hitting the sheathing. Or in an unoccupied space will the humidity be so low that no condensation will form?


Thanks for additional info.

Plumdog_2

construction heat

I used to keep several Sterling power vent gas unit heaters that I would rent to the homeowner or contractor for temporary heat. They could be vented into the B vent with a reducer or stuck horizontally out an opening somewhere; then hooked up with a long piece of CSST gas line. The 150K unit could easily heat a 6000 sq. ft. 3 level home from the basement; but it sometimes warped framing in the airflow. The 75K unit worked ok for "normal" size homes; and was much easier to move in or out.

KW_2

insulation?

plumbdog - were these homes insulated or uninsulated at the time? If uninsulated, did you have condensation on the wall or roof sheathing using the unit heaters (when it was below freezing outside)?

don_163

Kw

maybe you should go to hot tech topic and look for the professor explanation of humid air.

If you have a envelope that is not insulated and you're heating it the stack effect will cause more DRY outside air
to enter the envelope and help reduce any chance of your air
reaching its dew point.

So personally I dont see a problem while insulating,I can only see a problem after its been insulated.

Then we will be talking indoor air quality and floor dehumidifiders.

Good luck with your project.

jp_2

condensation

warm surfaces do not promote condensation! condensation will ALWAYS occur on the colder of surfaces. winter air tends to have every little moisture in it.

jp_2

heating air

if you heat air, you are going FARTHER away from the dew point, not closer.

Brad White_22

Yes, absolutely, jp,

provided the combustion products are vented away so that the absolute humidity remains at least constant.

Plumdog_2

Mostly insulated, but

I run one now in my garage which is uninsulated, because I have yet to finish it, and there is no problem with moisture forming. Those unit heaters dry everything out pretty fast.

KW_2

condensation

Yes, I understand that cold air holds less moisture than warm air - warm air is almost always *relatively* more moist than cold air. Seems like I'm asking a stupid question - but isn't what I'm asking (does warmed air in the structure cause condensation on the cold, uninsulated roof deck?) similar to when you place a cold glass of lemonade on the deck railing? The warm, relatively moist air comes into contact with the cold surface of the glass and you get condensation.

Isn't this the same as if you break into an exterior stud wall behind an electric box that isn't sealed? Warm, relatively moist air (generated by the furnace) leaks through the electric box and you get condensation and/or frost on the sheathing.

I'm getting the feeling that I'm asking a REALLY stupid question - I must be missing something really basic. Of course, better to display my ignorance in public! )

Somebody explain what I'm missing....

brucewo1b

KW

I think your question is fine I honestly don't have an answer, your looking at how much condensation will form on the cold wood not what is carried in the air. why because he needs the foam insulation to adhere to the wood.

Weezbo

KW, when you work at it in 50 60 below its a little different,

you do what you can and get it done.

you ask if you are missing something...well , in a word Yup. A lot of the reason that a general is hired is because he looks at the job and the help and materials he has available and lays out some totally unrealistic schedule *~/:)The guy usually cost a dime cause his license cost a few and the quality of his subs he usually knows and works with ..this unrealistic schedule however is far different from say a homeowner turned General contractor. the foresight isn't there for a homeowner...He has no idea that the only sheetrock delivery truck is in the shop for repairs the general is Painfully aware of it. as an example

do you have the plumbing and wiring rough ins complete and tested and the holes for the hrv all sealed? are the gables still open? do you have the place dried in? i mean this in a kind way.you have to see that some things are done in order...foam can be accomplished in dry areas.how about starting on say the garage first. then you could isolate it and work from there.

i would visquine the lid ,hammer the heat to the garage walls,are you putting friction fit in the dividing wall of the house and the garage? got plenty Rags?lots of fans? ever done this before

Before ?

Before What?
i like questions like that they seem to lead to other questions interesting and thought provoking though sometimes a little off topic ..that's ok though as the change of perspective usually helps more than the answer.

KW_2

yes

Weezbo,

Project is 100% drried in - garage and house. Plumbing/electric rough-ins done and inspected. Drywall is scheduled. Insulation is 3-4 wks late due to factors beyond anyones control. Have lots of rags and lots of fans. I've had the HVAC sub install temp heat source - forced air furnace. Hanging furnace installed in garage to provide heat. No, haven't done this before - in the sense that I've not used spray foam before - first time with that product and the conditions it requires. Plan was to start insulating in the garage and continue from there - except the garage is uninsulated and I have to heat it in order to foam it and not sure if running heat will cause condensation on the roof deck making it impossible to spray.

Weezbo

i take it you have a flat Roof that is hot mopped.

and a walk out deck veranda type thing on top with what we call a hot roof. where the insulation is seeing the cold with no ventilation between the that deck and the garage ceiling?

normally i would recommend a build up on Top of the plywood ,insulation, pavers , 5 ply hot mop("dead level"), like that.

sans that, taken from the inside you will have to "drive the heat out".which is a mis nomer for for driving the moisture out.once it is dry inside you still need to have that heat driven to the outside and get rid of the snow or whatever on the roof. even though snow is a form of insulation it is worthless on a hot roof. a green roof it would be ok .

one way to contend with the deal is to grasp the entire building as just something inside a building envelope. get visquine and wrap the entire building and pump heat into it. that is a way to finish :vynil siding, gable vents, soffits ,exterior trim, decks, railings, slabs, in substantially colder weather.

if you had a picture of the place it would be easier to visualize the quickest and best way to get it done.

Plumdog_2

Relative Ambient Humidity

I guess it depends where you are. Here in Colo. it is often so dry that wet clothes will dry out on the clothesline even when frozen. A cigarette butt out the window will burn 137,000 acres. Dry sinus's are epidemic. Cows turn to jerky while they are still alive. Down by the coast you can't dry anything no matter how hard you try.

jp_2

your close

first part is right.

second part you are forgetting an important part.

whats happening in that wall cavity is a little different. the air inside the house normally has increased humidity than the colder outside winter air. (humidifier running, showers,cooking ....

thats the difference.

heating air does not change moisture content.

if you just heat up a cold house there is no new moisture in the air for forming on those cold windows. otherwise there would be condensation before you began heating.

edit: this will work as long as there isn't a lot of moisture in the building waiting to be warmer and set free!
damp basement,rain soaked subflooring, .....