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Tanklets > Radiant Heating Problems

Radiant Heating Choices

Q: I just pulled the construction permit for a 1,347 sq ft addition to our house. It will be a one-story addition with only a master bath (one-head shower, two sinks) and a laundry room, as far as domestic hot water goes. I am also planning on radiant heat. It seems reasonable to want to combine heating and DHW duties into one unit, but I'd like to get some advice on that.

I've read enough about tank-type, normal and condensing style, tankless and boilers to be a bit confused about which really are the best, or at least the best for my situation. Other notes: I have a gas fireplace that is next to the addition. It could possibly supply the gas line. It may not have a big enough diameter for a tankless, though. What is the outside diameter of a gas line that is big enough for tankless use? Also, would it be better to employ two water heating units, one for radiant and the other for DHW?

A: It's best not to mix heating water with drinking water. In some areas it's even illegal to do so. A single heater can be used if a heat exchanger is used between heating and drinking water. Efficiency-wise, there are all sorts of ways to do things. If a boiler is used, than a storage tank heated by the boiler is a good way to go for potable water.

A mod-con, or modulating, condensing boiler is the wave of the future for efficiency and performance. If you have heat loss calculations done for the addition, it will guide you as to equipment size. If you go to extremes to make the addition more efficient, you could actually save money by not having/needing as much in the way of heat making and distributing equipment.

Look into structural insulated panels; SIPS. Normal/nominal pipe size is the interior, so 3/4" is really more like 1" outside diameter, when talking steel pipe. A gas fireplace will only have a 1/2" line, and you are talking about supplying a heating source for space, water and maybe a dryer. 1/2" won't do that. -- Larry

Q1: Hi Larry. Thank you for the information. 1) Seems like I've seen the boiler for combined radiant heating and DHW (with storage tank) at a friend's new house and at a model home. Is this a reasonable way cost-wise? Is a Munchkin a mod/con boiler? 2) What about a "Voyager" or Polaris hot water heater? Would there be benefits, cost or efficiency or ease-of-installation, with one of these units performing both tasks? 3) Looking for a recommendation. Which way would you go? Boiler w/ storage tank, Voyager type unit, or two regular water heaters, or tankless or ? I live in Albuquerque (winter is chilly but not mid-west or east coast cold) and I am planning on 2x6 walls with good insulation. I looked into SIPs and even ICFs, but couldn't justify the cost.

A1: You've named three major makes of heater that could be used to do both potable water and space heating. I should know off the top, but don't about modulation. Heat Transfer Products is the source for Munchkin. http://www.htproducts.com/

I'm certain heat loss calcs are necessary for knowing what equipment is needed. You need calcs that give you heat loss per room, so the radiant can be sized correctly. At http://www.heatinghelp.com they have a free sizing calculator. They also have "The Wall" where you can ask questions of folks with far more experience with radiant heating (and cooling) than I have. I wouldn't compare SIPS or ICFs to conventional framing directly. Using these systems, your need for space conditioning equipment is reduced dramatically.

So, it's better to compare project costs as a whole. That is compare traditional framing and a bigger heating system, with say SIPS and a small heating system. Don't forget the ongoing cost of the bigger energy bill with less efficient framing, (even 2by6s). Air leakage is a big factor that conventional framing doesn't handle well, while both SIPS and ICFs are quite snug. One other thing you might want to do is stop by Zomeworks and see the variety of things they have to offer. http://www.zomeworks.com/ They are working on some pretty interesting solar heating and cooling gear. -- Larry (12/22/07)

Sediment Removal

Q: I read with great interest your Rescue site and have a couple of questions that I hope you would be kind enough to answer: I recently purchased an older home that has quite a weird setup for heating. It has an oil furnace and the upper floor is a forced hot air system.

The basement, I guess, was finished off afterwards and has hot water baseboard heat. The basement system works off of the hot water heater. This presents numerous problems because the water is not hot enough to get the temperature up over 68 degrees. No one will assist me in increasing the water temperature for fear of scalding. I checked the water at a faucet with a thermometer and the hottest is 137 deg..

The hot water heater is a Bock unit, about four years old. Unfortunately, I read your instructions after I had the anode rods changed recently and the plumber installed aluminum rods! My question is how to drain sediment out of the tank? I have been told that it is difficult to do because the downstairs heat comes off of the water heater also!

I have reason to believe that there is a lot of sediment in the tank, but feel helpless to remove it since no one around here seems to know how. Do you have any ideas? I would sincerely appreciate any help. Thanks. Have a nice day!

A: First, I apologize for the delay in answering. My computer was in the shop last week and I only got it back yesterday. You have several separate problems. For your radiant heating troubles, I'd suggest you contact Dan Holohan at http://www.danholohan.com (now it's http://www.heatinghelp.com). He lives in New York and he's an expert on radiant heating systems.

As for the water heater, neither of us has ever seen a Bock, although Larry says they are fine heaters. There are two possibilities for cleaning it out. One would be to put in a curved dip tube and ball valve drain assembly and just flush it. You might have a plumber do that when he replaces the aluminum anode rods with magnesium ones. The other is that Larry said he thought there might be a cleanout hatch. Most residential heaters don't have them, but he thought a Bock well might.

The plumber would simply open the hatch, drain the heater, scoop out any gunk that's settled into the bottom of the tank, and then reseal the hatch. If it happens that you have greater than 3/4-inch-diameter plumbing coming in and going out of the heater, you won't want to use a curved dip tube, since it will restrict the flow to your system. Then the cleanout hatch might be the more likely solution. -- Randy (1995-2000)