How long is the string?

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In the midst of a hot hot summer, thoughts turn to the next cold cold winter and, in a rare attempt at forward planning, we're working out how to efficiently and cleanly heat the house. Hydronic heating may be the answer. Yesterday, we had a visit from an installer who, reminded by a phone call, arrived three hours after the appointed time. He was nice enough, with tens of years of experience in hydronic installations and much advice to hurriedly offer but, alas, not so good at listening. Cost will be an issue and we don't want to do the entire house, which is an unusual requirement since we should be concerned about house resale value. We need radiators that won't gather dust, any dust, and hence are overly suspicious of designs with vents and grills. In the back of the mind, there's the nagging question of how long we'll stay in this house; and the answer to that depends on how long recovery will take; and that, it seems, is related to the length of a proverbial piece of string. Investigations continue.