[AC_Hacker]

Originally Posted by opiesche

...I meant 6" exterior walls with fiberglass roll insulation. I didn't do it myself, but have opened some of the walls (to run new power outlets), and that's what I've found in two of the exterior walls. The windows are relatively new (late 90s or so), and are double pane vinyl. The attic is insulated with about 6" of loose fill fiberglass (something I plan to augment with additional batts in the future).

Not too bad... but as we in this forum have found out, the R-ratings for various insulations are determined in lab conditions with NO INFILTRATION. This means that if you have a wall with holes for power wires and outlets, you will get infiltration and you will not get the full insulation that you have paid for. Some homes are now being built with a separate, inside, 2" utility partition, an all power and water intrusions and power outlet and switch installations take place there, leaving the insulated wall intact and air-tight to work to maximum effect.

...Just saying that things can be much better than they have been in the past... because in the future it may be very important.

Originally Posted by opiesche

We didn't do a full heating load analysis - our estimate came from the fact that my parents' house sees temperatures at least 35 degrees below what we experience in winter. They've got double the density of heating loops, and similar insulation, and about the same water temperature (they have in-slab loops over a basement though). So we figured that half the density would work fine for us with the relatively mild temperatures we're seeing.

I'm sure that your new system will work just fine... you will be warm and comfortable and rightly, proud of your new installation.

But some of us here are trying to go beyond that and are eagerly venturing into the realm of 'diminishing returns'. As you surly know, when you DIY, some projects that when hired out, might not 'pencil out' in a favorable fashion, and when done DIY, they actually become not only do-able but quite desirable. For instance, I assume that your parents in Germany are using pipe spacings at around 6", or whatever the metric equivalent is... it does make sense to widen the spacings to 12" inches in your locale because your weather is so much milder, and with natural gas dropping in price, tighter spacings would not pay off in your lifetime.

However, if you had used the same spacings as your parents, it would open up the possibility of using low intensity heating to it's best advantage. Low intensity heating could be something like solar heating, where feed water only occasionally gets up to the temperature level that you can rely on with natural gas.

Also, another low intensity method, heat pump systems greatly benefit from higher efficiency floors, as they don't need to raise the temperature as high to warm the home to a comfortable level, and thus don't have to do as much work. The benefit to you is much lower power bills.

Originally Posted by opiesche

Your information about average temperatures seems roughly correct. There's a couple of weeks or so when the temps occasionally drop below 30 for a few hours (between 3 and 5am), but that's the worst we see.

We've never done a blower test, but the house seems reasonably infiltration proof from the fact that it's the front door doesn't easily slam if all windows are closed.

This all sounds very good!

Originally Posted by opiesche

We haven't yet done any underfloor insulation, which is still on our list of things to do (I'll probably hire a few students from the nearby colleges to help because I don't fancy the idea of scooting around on my back in a 15" crawl space for several hours :P). It'll likely be fiberglass batts with tension wire to hold them in. The foam underlayment of course insulates a little, so I plan on insulating very well in the crawlspace to offset that.

I have one of those crawl space insulation jobs coming up too, and I'm not looking forward to it.

But when you mentioned the foam underlayment, is it over or under your hydronic floor?

Originally Posted by opiesche

As for the water (this is still upcoming, as I haven't actually hooked it up yet), I'm going back and forth between a dedicated 30 or 40gal natural gas water heater (the total water in the system is about 25 gallons for the 1/2" PEX) and an air source heat pump. The water heater is going to be much cheaper and should be pretty efficient, although not as efficient as a heat pump of course. I think it'll strike a pretty good balance between upfront and runtime costs.

If you go with a larger size water heater (maybe even bigger than 40 gal), it will reduce the frequency of the 'heat-up' cycles. There is an efficiency curve that describes each firing of your water heater... the efficiency increases in the beginning of the firing, and levels off until the end of the cycle. By having fewer and longer firings, you will reduce the overall lower efficiency part of the cycle.

Originally Posted by opiesche

Since I've got only 9 or 10mm of the bamboo flooring and the thin underlayment on between feet and heating, I figure 80 to 85 degree water temperature should be sufficient, but that and the flow rate is something I can play with and fine tune to the needs of the rooms. Regulating the temperature is likely going to be done just with the water heater itself - I'll set it so that the temp ends up about 85 degrees (a thermometer in the feed line to the manifold should do the trick) and the water will be pumped from there directly to the loops. That way I don't have to mess with a second cold water line and a mixing valve.

I'm very interested to see how it all works out. One thing we very badly need is a database of performance from DIY installs.

Originally Posted by opiesche

Edit: I haven't thought too much about the thermostat yet. I figure I'll regulate the system by outside temperature - if it drops below a certain level, it turns on the pump. It'll take some experimenting to find the right setting, but should work. Since I don't have the tubing in concrete or other large thermal mass, there should be relatively little delay between turning on the pump and the floors warming up.

There are dual-sensor thermostats that are specially designed for hydronic heating, for applications exactly like yours. They cost maybe $200 or so. They even have an adjustable setting to find-tune for the thermal mass of your house, so that there is minimum over-shoot or under-shoot.

So, that's my take on it. I must confess that I have not put a hydronic system into my house yet, but I have been obsessively studying hydronic radiant floor systems for almost a decade. I am very interested in low intensity heat, as I am convinced that the future lies in that direction.

I'm hoping that Vlad will chime in here, as he has done a very good job in his house, and he has no shortage of opinions. He did not go the 'utility wall' approach when he built his house, but he did compensate with post-construction infiltration sealing that was phenomenally thorough... I've never seen anything like it.

Best,

-AC_Hacker