# Excess heat in the sunroom



## Ed Norman (Jun 8, 2002)

We built a 12X22' sunroom with 10' high 8mm double wall polycarbonate walls. We insulated the 6' ceiling and put 2" of foam under the concrete, plus laid in radiant heat tubing for future use. A sunny day gets the room up close to 100 when outside temp is in the 40s. We haven't even finished calking and sealing everything tight yet. Last winter it was over 80 on a below zero day, and there was still a dirt floor.

We open the front door of the house leading to the room, and open the big window into the room, and let the heat roll into the house all day. It keeps the house warm until long after sundown.

What else can I do with the heat? We're working on a thermostat controlled fan and a duct to blow warm air to the back bedrooms. Could I make something to plumb into the radiant tubing to heat the floor? I've been thinking of using solar to heat the floor, instead of propane. The roof above the sunroom would be fine for a heater. With a closed system it could be full of antifreeze, but we usually get a few nights of -35 F here every winter.


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## wy_white_wolf (Oct 14, 2004)

Does the room maintain temperature through the night?

If yes, then you propably could pull some heat off for the bedrooms. 

If no, then you need to increase the thermal mass of the room to absorb the heat and radiate it back throughout the night.

Adding solar panels on the roof to heat the floor is only going to make the overheating problem worse. Best to use that heat elsewhere.


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## Ed Norman (Jun 8, 2002)

It doesn't maintain temp all night. We will only pull heat off when the thermostat says the sunroom is hot enough. If we suck out all the heat, the fan will stop. 

The radiant floor will be used to start plants in the early spring. That is the main time we are wanting a constant temp throughout the night. But if we could get the slab heated with solar, we could use the residual heat later into the evening.


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## SolarGary (Sep 8, 2005)

Ed Norman said:


> We built a 12X22' sunroom with 10' high 8mm double wall polycarbonate walls. We insulated the 6' ceiling and put 2" of foam under the concrete, plus laid in radiant heat tubing for future use. A sunny day gets the room up close to 100 when outside temp is in the 40s. We haven't even finished calking and sealing everything tight yet. Last winter it was over 80 on a below zero day, and there was still a dirt floor.
> 
> We open the front door of the house leading to the room, and open the big window into the room, and let the heat roll into the house all day. It keeps the house warm until long after sundown.
> 
> What else can I do with the heat? We're working on a thermostat controlled fan and a duct to blow warm air to the back bedrooms. Could I make something to plumb into the radiant tubing to heat the floor? I've been thinking of using solar to heat the floor, instead of propane. The roof above the sunroom would be fine for a heater. With a closed system it could be full of antifreeze, but we usually get a few nights of -35 F here every winter.


Hi,
A lot of this sounds good to me. You have a sunspace that generates a lot of heat like they are supposed to. 
You might try finding a more efficient way to transfer excess heat to the house. In the wall that joins the sunspace with the house, a lot of people use a fan up high to blow hot air from the sunspace into the house. You also need a return vent down low in the wall to allow house air to flow into the sunspace to replace the air you are blowing into the house. The book listed below tells you how big these vents and fans need to be. This should move a lot more air than an open door does, and should cut your home heating bills.

As far as keeping the sunspace warm enough at night for plants to grow. I'm not a gardener, but I belive that a lot of plants will do OK if at fairly cold temperature -- not as low as freezing, but lower than we would be comfortable in. 
If the sun shines on the concrete floor, the floor should warm up during the day, and then return this heat at night to keep it warmer. A dark color on the concrete would help it absorb a better. 
Beyond this, you can add thermal mass. Probably the easiest way is water filled barrels or containers. Water is very effective thermal mass -- about twice as effective as concrete on an equal volume basis, and 5 times as effective on and equal weight basis. The water containers should be dark colored and in the direct sun.
If you get more mass in the sunspace, it will not overheat as much during the day, and it will not cool as much at night. The tradeoff here is that the sunspace will have less excess heat for the house -- its a balancing act.

The other way to reduce temperature drop at night is some form of moveable insulation shades or panels over the glazed areas. This will dramatically cut night temperature drop, but you have to be there to move the panels twice a day. I think that some people do this only when very cold weather is expected.

Another way to control overheating is the greenhouse style ventilation that pulls in air through low opening "windows" in the greenhouse wall, and blows air out near the ceiling with a fan. Most greenhouse supply places have these. 

A very nice book on sunspaces that covers all the ins and outs of using a sunspace for both house heating and plant growing is: The Homeowners's Complete Handbook On Solar Greenhouses and Sunspaces", Shapiro

Its out of print, but available for next to nothing at Amazon.com used books and the other online book places.

More Sunspace info on my site:
http://www.builditsolar.com/Projects/Sunspace/sunspaces.htm

It sounds to me like you did a really good job on building a good sunspace -- its just a mater of getting the thermal mass and the heat distribution to the house right -- don't give up on it 

Gary


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## raymilosh (Jan 12, 2005)

I agree with Gary's recommendations. There is so much heat coming in so fast that the mass in the room is not capable of absorbing it, so it heats the air, too. That can be good, because heated air is easy to move to other places in the house. If you want to store more of the heat in the sunroom, though, I suggest making the room's furnishings such that sunlight hits as much of the floor as possible...no rugs, no big tables, unless they're glass topped, etc. Also if the floor isn't a dark coler, make it darker. Acid stains are fun to apply and create a really cool looking floor. Read up on it.

If you already have a dark floor that isn't shaded, then more mass will keep daytime temps down. 
It sounds like your question is what to do with the excess heat, though. I'm thinking easiest way to get heat moved around the house is via the air, so the air handling system will work well to move excess heat into the back rooms. I doubt the floor would get warm enough to harvest the heat in the radiant tubes for use elsewhere in the house. 
I made roman shades with a layer of mylar inside them for all the windows on my passive solar house. I think they did more to conserve heat in winter (and prevent heat in summer) than anything else I did. Way more than I was expecting. Definately make your self some shades or mobile insulation like gary suggested. 
My last idea is to install a batch heater in the sunspace. I made one out of dead electric water heater tanks painted black plumbed inline placed inside a well insulated double glass covered box wity an insulated lid to prevent nighttime heat losses. The inside of the box is shiny to reflect heat onto the tanks. The hot water could be used for your house hot water needs and any heat losses from the batch heater are still inside the house.
If you want to use the water in those tanks for heating the floor or if you want to heat it further for domestic use on cloudy days, install a waterjacket in the woodstove (assuming you have a woodstove) and let it thermosiphon scalding hot water into the tanks and/or into the floor. I did this in my house. It took lot sof time and experimenting and I have some additional improvements to make to increase efficiency. If you want to hear more about it, ask and we can talk more.
ray


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## Ed Norman (Jun 8, 2002)

Since we just poured a step outside yesterday, the east door was removed all day today. It was real windy. When I got home this afternoon, with a strong wind and temps in the mid 50s, the room was 96 and breezy. The concrete had heated up to 69. This evening I went out and checked and the room was now 68, and the concrete was 68. 

I am gathering the parts for the fan project like Gary talks about. Due to the layout of the house just inside the wall, we need to run the air down a duct to the back of the house. If we blow it right through the wall, most of it will go straight upstairs, which is already the warmest place. I can gather hot air from the sunroom ceiling then duct it down between studs to the crawlspace, then back to the back bedrooms. I had not thought of a return duct but that is a very good idea. 

No woodstove in this house. We've cut enough in the past and insurance was happy to not see one and we got just a bit lazy, maybe. 

Barrels of water will be easy to do.

So will curtains. I see Farmtek sells several types of curtain material for this use. I did a thread on floor coverings earlier and we have almost decided to go with cheap tiles, probably dark red. The concrete has to cure a while longer before we tile. 

Overheating was not a problem this summer. Due to dumb luck when we built it, there is just enough eave to shade the glass in summer, and as soon as the weather in the fall cools and the sun drops lower, the sun comes in and starts heating. We can also replace the doors now with screen doors all summer. 

I'm sure after we get all the glass caulked up and get the beadboard ceiling up so the insulation is covered, we can get 10-15 degrees more heat out of this thing. It was very cheap to build ourselves and is really saving propane.


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## mdharris68 (Sep 28, 2006)

Do you have any pictures of your sunroom?


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## Ed Norman (Jun 8, 2002)

No, but since you asked nicely, I'll try to take some tomorrow.


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## Ed Norman (Jun 8, 2002)

Maybe this picture link works, maybe not. 

http://img205.imageshack.us/img205/5217/20071013002yr9.jpg


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## mdharris68 (Sep 28, 2006)

Ed, thanks for posting the pics. Now that I know what kind of glazing you used, I was wondering if that is something you found locally or if you had to mailorder it? I was searching for it on the net and found some but it seems like shipping made the price very high. Thanks again for the pics.


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## Ed Norman (Jun 8, 2002)

We got a Farmtek catalog several years ago. It was our first one. I thumbed thru it and noticed the closeout section and they had some 8mm double wall polycarbonate sheets, 6'X10', on closeout. I got interested and sketched out a sunroom. Then I noticed a sticker on the front of the catalog saying free shipping on your first order, plus 15% off. I called and sure enough, they gave me free shipping, 15% off, a dozen pairs of gloves, and a rolling soft cooler. I couldn't believe it. Everything showed up at our farm store where truck shipments unload. We took a trailer and they loaded a huge pallet of polycarbonate up for us and we were in business. If I had to order at full price and pay shipping, I wouldn't have. Once in a while you just get lucky.


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## FrodoLass (Jan 15, 2007)

Ed Norman said:


> Maybe this picture link works, maybe not.
> 
> http://img205.imageshack.us/img205/5217/20071013002yr9.jpg


That's really awesome. Thanks!


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## Al. Countryboy (Oct 2, 2004)

Ed after reading your post on using the heat from your sun room I wanted you to know that a few years ago we had a hi-tech solarium built at the back of out two story home. It faces the south also. We are in Alabama and we do not have the cold winters as you have. The solarium is 16x48 ft. On our coldest clear winter days temps.(maybe around freezing) the greenhouse/solarium can reach over 100 degrees. We have two small fans at each end so I vented one of these into our master bathroom off our bedroom. I cracked a couple of windows in a couple of the other rooms to let the cooler air circulate back into the greenhouse while the fan was running. We thought how great this worked, but after about 2 weeks began to notice that we where getting a dark looking mildew, mold or something at the tops of some of our rooms and also in one of our upstair bedrooms which we had never had a problem with before. We finally had to remove vents and cover holes leading into the house because of the moisture rich heated air intering the house. We do at times open the solarium doors on up in the mornings when temps. reach close to 100 and let some of this hot moist air out. Then close the doors open the kitchen door to let the heated not so moist air in. We do not do this on a daily basis and have not had this problem again. Most of the solarium top is also glass and boy does it heat up fast. I do think that we really benifit just from the heat in the solarium that heats up the walls at the back of the house though.It could be that you will not have this problem, but might want circulating the air with a few fans before putting in alot of vents,hard work and money to find that it might not work as we did. Almost posted a few days ago, but did not want to bust your bubble. Possibly do a little experimenting first. I am always experimenting and trying different things. Some work. Some don't. This one did not. Good luck.


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## Ed Norman (Jun 8, 2002)

Thanks for the input. Around here, humidity is never a problem, it is dry air all year. Mildew is an endangered species.


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