Today's tight homes (little latent load) combined with ventilation ducting (ERV/HRV) are making radiant cooling (and off-peak cooling storage) more feasible. It requires dehumidification and attention to room pressures (you want slightly positive pressure to prevent humid air from coming through leaks vs coming in through the ventilation system). See "DOAS" for more info.

Highly insulated homes make fewer heat sources feasible, but in most cases, it's going to require open interior doors.

I just got my latest Log Home magazine and in it is an offer for a free heat gain/heat loss analysis from Unico System. I have sent them my plans, we'll see what happens...

We design and install Unico High Pressure systems. They will give you a block load; adequate for appliance sizing but insufficient for radiant floor design.

I wanted the radiant for comfort, but am being told that geothermal may not even produce enough hot water to heat the house.

There is no reason geo can't work with radiant, but it is a sophisticated system that not just anyone can design or execute. Clearly whoever told you that has no understanding whatsoever of the systems.

I'm afraid with an air geothermal system all my heat will be up in the cathedral ceiling. Distributing the air conditioning is another nightmare, but my main question is will a geothermal system work with radiant heat in this situation, and is the cost worth it?

Air distribution is not as tough as some think, the bigger problem is people take the lowest bid and get a code minimum duct system thus tanking the distribution.

Is radiant worth it? That is truly eye of the beholder stuff. Few things are more expensive than geo-hydronic systems where even the control package can run thousands, but there's nothing like radiant for comfort.

As for value, the "geo" system is more in question since payback in residential applications can easily match expected life.

In the latest IRS ruling I've seen on the tax credits, while duct work has been specifically excluded, radiant delivery has not. This closes the gap quite a bit between gas or electric versus geo water to water heat plants. In our neck of the woods it means about a ten year payback for added expense.

I think the geo system is just way too expensive, even with the tax credit. We have 2 different quotes in the mid to high $30,000s, before the credit.

How much is the other system you are proposing (installed) including additional infrastructer from the electrician which is covered by the tax credit for geo. You might not be as far off as you think but I'll grant you for an intermittent use vacation home you are piling on a lot of first cost.

Today's tight homes (little latent load) combined with ventilation ducting (ERV/HRV) are making radiant cooling (and off-peak cooling storage) more feasible

Monitoring dew point to avoid condensing in unwanted places (like radiant floors) takes quite a bit in controls to safe gaurd against. We put one in mid MI and found the Tekmar controls "klunky" at best. I think the cost v benefit simply wasn't there.

I just got my latest Log Home magazine and in it is an offer for a free heat gain/heat loss analysis from Unico System. I have sent them my plans, we'll see what happens...

At the end of the day, whoever installs the system needs to do their own load calcs so that they "own" the results. FYI personally I find the HV duct systems often tank the cost v benefit scale particularly in new construction where you don't have to fish duct in finished cavities.

You seem to be stuck in between old fashioned building and the new super efficient methods, and this is being reflected in the responses to your original letter. We now know how to build good houses that work and are amazingly comfortable and inexpensive to heat and cool. (Mostly based on Passive House ideals). But your are choosing to build a "log cabin" which is definitely an older style and difficult to seal, insulate and heat compared to PH inspired houses. You cannot have it both ways. If you are set on the log cabin, spend the money to get some type of a good "traditional" system designed and installed. Radiant is possible, but you may need more heat than what that can supply, so be prepared. If you want to save money and be comfortable in your future years, start with the house design and do that.

Joe is my new Geo hero. Succinct, accurate and balanced.

Bob has it right. You can't have it all.

You are building a log home and you want to be comfortable. If radiant heating can't make you comfortable someone has made a serious mistake.

We design and install Unico all the time and have used the factory--one guy thousands of plans--in the past. Great system but you must your own experienced Unico installer. The advantage is superior latent heat control and ease of installation. With the new Unico iSeries efficiency is more than acceptable.

"I wanted the radiant for comfort, but am being told it is not worth the extra expense, or that geothermal may not even produce enough hot water to heat the house. "
This depends on the "design load" and having the system designed for that specific house.

"Oh, we will spray the underside of the first floor with closed cell insulation."
Closed cell is no better than other insulations, just slightly different. It's a mistake to think that pasting whatever latest gizmo's you choose - whether spray foam, geothermal or mini splits, onto a conventional house will give you any specific results. You need to start from the beginning to get a certain result.

"I just want to be comfortable"
The best reason for designing and building a good, modern, Passive House inspired home.

"I'm afraid with an air geothermal system all my heat will be up in the cathedral ceiling."
Which it will unless the house is built properly. No amount of lipstick will solve this, but it isn't an issue with the type of homes I'm talking about.

Radiant is possible, but you may need more heat than what that can supply....

Bob, I'm not sure the intended message here, one can always supply enough heat with radiant. If you mean the floor might not be big enough in the great room, that may be true, but the floor could be augmented with radiant panels, walls or ceinlings.

That said, I'm with you; minimizing the load is the shortest path to affordable comfort. With some amazing looking log siding, SIPs and timber frames, and having seen some epic log home disasters I'm not on board with the alleged thermal mass advantage touted by proponents.

Shucks Badger I'm flattered.

Joe- I understood that susanm wanted to do in-floor radiant heat which as you indicated, may not be enough.