Q. What is the best space heating system?

A. We think in-floor, hydronic heating is the best. It feels more comfortable than anything else because you have warm feet and a cool head. When this is the case, you feel warm and alert in a cooler room - you're more comfortable and use less heating energy - the best of both worlds. Conventional heating systems do the reverse - you tend to have cold feet and a warm upper body. You can feel sluggish from too much high heat but still not warm.

Q. What do you think about heating with electricity?

A. Not much. Using electricity for any kind of heating (stoves, water heaters, space heaters) is the most inefficient, expensive, and non-appropriate way of using it.

Q. What can I do to save on my heating bill? I've already insulated as much as possible, caulked and weather stripped around windows and doors, as well as adding window covers.

A. The average US home uses 57.3% of its annual energy budget for space heating, much more in the colder climates and during the winter. It sounds like you've already taken care of some of the more important basics. One other question to look into - Are you heating rooms you don't use? If so, consider installing zone heaters. They give extremely high efficiency and let you heat only the spaces you use.

Q. Is there anything I can do to help offset the higher cost of hydronic heating?

A. Heating/plumbing contractors charge high rates for installing these systems. You can do at least a big part of the work yourself though. You could also hire a less expensive handy man or plumber and help them figure it out. We can do the heat loss calculations, supply the components, and send CAD drawings and installation instructions.

Q. Can I use a demand hot water heater in a hydronic heating system instead of a more expensive boiler?

A. Boilers are normally recommended but we know many customers quite happy with Aqua Star demand waters used this way. They aren't really designed for this use and boilers have several advantages. But you could save hundreds of dollars. Especially for smaller spaces, a demand water heater may be the best choice. We can send you a plumbing schematic showing all the needed components and how they fit together.

Q. What are the differences between a direct vent, vented and unvented gas heater?

A. Vented heaters vent fumes outside. Direct vent heaters cost more but use outside air for combustion. They also normally mount on a wall - this makes them easier and less expensive to install. Unvented heaters shut down if oxygen gets low. This is great for safety but not too good for keeping you warm. Unvented heaters less than 10,000 BTUs are approved for sleeping rooms, less than 5,000 BTUs for bathrooms. Larger sizes are not approved or recommended for sleeping rooms.

Q. We would like information on Radiant heat under tile floors...have no prior experience...

A. The first thing is to do the heat loss calculations based on insulation, windows, ambient temperature, etc. Even before that though, the first decision is if you want a radiant heat contractor to do the work, an independent plumber, or do it yourself. We could help if you choose of the last two, not if the first.

Q. Just noticed that there have been some modifications on the aquastar tankless heaters. We are considering hydronic heating, can you tell us about the new hydronic unit?

A. The main difference is in the water valve assembly. The "low pressure" hydronic model is made so you can get a higher flow rate without reducing the pressure. In practical terms, this means you can use a conventional recirculating pump - with the standard model, you would need a much larger pump and still not be able to generate as many BTUs.

Q. I think the 170 sounds like it might suit our needs better than the 125...is there a 170 hydronic unit available?

A. There is also a new Model 170 designed for hydronic systems - add $125 to the normal 170 price.

Q. What are the advantages of using a tankless system for heating?

A. Efficiency and cost. For larger systems though (needing more than 100,000 BTU's), a boiler is more appropriate.

Q. I live in a very sunny area, and are very interested in building a solar heater in my home roof. Where can I find information about design and parts needed to built one?

Ricardo Agudelo
Maracaibo, Venezuela

A. Let's see: if 4 people wash dishes and take showers for 10 minutes every day with 20 liters per minute of 40 C water, and the incoming water is 20 C, we need to heat 4x10x20 = 800 liters of water, ie 800 kg, by (40-20) = 20 C, which means collecting 800x20 = 16,000 (capital C) Calories or 4.19x16,000 = 67,000 kilojoules (about 65 K Btu, since a Btu is about 1 kJ) or 50 MJ/3.6 = 19 kWh per day of solar heat, worth $1.90 US per day at 10 cents/kWh. I wonder how much your electrical energy costs, when it's available. Duffie and Beckman's solar engineering book says the coolest month in "Maracibo, Venizuela" (is that the same as Maracaibo, at latitude 10.6 S?) is December, with an average outdoor temperature of 27 C (80.6 F) and an average daily 14.4 megajoules per square meter (4 kWh/m^2 or 1270 Btu/ft^2) of sun that falls on a horizontal surface. If there were no thermal losses, it looks like 5 square meters of solar collector would be enough. (The book says Caracas is cooler, with 20 C and 13.5 MJ/day in December.)

I wonder what the roof is made of. Wood? No we don't have wood constructions here, the housing here is rather masonry. So it's a masonry roof... Does a part of the roof face south? No, is in east-west direction, but as we are 12 over the equator, I think it doesn't affect too much Sure... How much is the slope of the roof? About 10 degrees, but I'm thinking in a flat section of 32 square meters Sounds like a nice flat section... I suppose its reasonably strong. No snow. Won't rot underneath. Making a water heater there might be easy... Does the temperature where you live ever drop below freezing? We would love that!, we are about the hundreds all year around. Locals have a season near christmas they call "los Hielitos" (The little ices) when it drops about the nineties. The water heater can be simpler if it never freezes. How about a shallow pond on the roof, with a black plastic pond liner underneath and a transparent plastic film cover? Keep it filled with a float valve, or rainwater that falls on the cover, to make a gravity-feed hot water system? Or make it deeper, like a hot tub? What combination of area and depth can supply most of the hot water needed for a day or two with only a small change in temperature? Suppose we try to make the water 130 F on an average day, and ask it to stay at least 110 F for 48 hours with no sun. If the box has good insulation underneath and on the sides, and a US R1 cover (one or two layers of greenhouse polyethylene film), after 48 hours, 110 F = 80.6+(130-80.6)exp(-48/(RC)), so the time constant needs to be at least RC = -48ln((110-80.6)/(130-80.6)) = 24.9 hours, ie we need a water depth of at least 24.9/64x12 = 4.7". The daily heat loss from the box would be about 24h(130-80.6)/R1 = 1,186 Btu/ft^2, and the daily solar gain is about 1,200 Btu/ft^2. Looks like we need more layers of plastic film, or solar concentration or nightime insulation. The night insulation might be a 3" thick rigid foam cover that automatically folds up during the day and folds back down over the box at night. With a used automobile windshield wiper motor and a photocell and a couple of diodes and limit switches to control it. A small PV-panel might charge the battery, and also act as the photosensor.

Sounds like a nice product for The Sustainable Village. This system might be inside a small greenhouse, if you have lots of wind. The foamboard would lower the losses to something like 700 Btu/ft^2/day, so the box needs a top surface of about 50K/(1200-700) = 100 ft^2, about 9 m^2. If the water were 12" deep, the box would weigh about 6,400 pounds, and might have 300 ft^2 of US R20 surface, ie a thermal conductance of about 15 Btu/h-F. If the water inside had an initial temperature of 130 F, and the box were closed up for 48 hours, it would lose about 48h(130-80.6)15 = 36K Btu of heat, cooling the water to about 130 - 36K/8K = 124 F. Adding 1600 liters, ie 3500 pounds of 80 F water to the box would lower the temperature to about (124(6400-3500)+80(3500))/6,400 = 100 F.